:.: :,)i:.j
THE I]NIVERSITY OF MANITOBA
Newly Covered Grass As HabÍtat For Fish In Bung BoraPed, Thaíland
by
Plodprasop Suraswadi
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATED STUDIES
IN PARTIA], FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF ZOOLOGY ,;,.;ti:..tl
:':-r:'::'il':l I,üTNNIPEG, MANITOBA
FA].L, L976 ..NEWLY COVERED GRASS AS A HABITAT FOR FISH
IN BUNG BORAPED, THAILAND''
by
PLODPRASOP SURAShIADI
A dissertation sub¡nitted to the Faculty of Graduatc Studics of: thc Univcrsity of Manitoba in partiat full'illnrcnt ol' thc rcquirctncnts ol'thc dcgrcc ol'
DO(]TOR OF PHILOSOPI{Y @ ï976
Penr¡issir¡rr l¡as bcc¡r grantcd to thc LllllìARY {)¡; T'llU UNlVEll- Sll'Y Ot; ùlANlT0lJ^ to lcnd or sell copies otì this clisscrtittiou, ttr the' NATIONAL LIBRAI{Y OF (:ANAI)A to nricrolittn this dissertation and to len The author reserves other publication rights, and neithcr the dissertation nor extensivc cxtracts lionr it uray be printed or utltcr- wise reproduced without tltc autl¡or's writtcn purttrission. ( .:._ ,f,l:,!:,41,:_' Ì.::i.: j,i,:"t.Ì:;f rl.:, ...1::." i::1::.-t::i-. r:.1. :i.:,: ::ì-i t:l:-::: .::::,a,:-,::: !"j:1:"-.::"::a:: t,t-,1 'rl1:ï::::: ):'-1. .... tt DEDICATION To my mother K00NY ING KRONGTONG SURASI^'AD I with great respect and-my fondest love. lt¡ ABSTRACT The characteristics of the grassy habitat, weed covered habitat and open water habitat are described in relation to succession stages. Fish fauna, ,,,, _:. "l stomach contents, benthos, vegetation and associated fauna, water and sediment brere determined. The'effect of continuous water cover on grass-covered habitat *"s evaluated, .l in the attempt to immitate the early succession stage after ' draining and refi l l ing. Information mechanisms ,i about the invoìved in the nutrient cycle and the :,, effects of water level variations on the food chain were obtained. The ¡nter- . I relationshÌp between flora and fauna, especial ly-the advantage of grasses compared to floating weeds for locally important fish species, was studied. This information will be used to improve management and increase fîsh production in Bung Boraped and other reservoirs of Thailand. ' The established grass-covered habitat represents the early impoundment stagecharacterizedbyrapiddecomposition,abundanceofnutrient,highproduc- tionofbenthicorganisms,invertebrateSaSSociatedwithemergentgrasseSandsmall r f ish. The so.i I had lrigh organic matter and a high phosphorus content. ,'j' : -.... Leersia hexandra, Hymenachne pseudoiterum and Cynodon dactylon were the major , , macrophytes. The increas.ing populations of such fish species as Tr.ichogaster pectoral is, T. trichopterus, Cyclochei I ichthys enoplos, Amblyrhynchichthys truncatus, Lusionsoma bleekeri and Anabas testudineus indicated high ecological p roduct i on . The weed-covered habitat represents the late succession stage, charac- terized by low production of benthic organisms and fish, and unfertile soil sediment. The obnoxious plants such as Eíchornþ qrassipes,' Salvinia cucullaiqq, ¡V lsachne globosa and Coix aquatica were abundant and HrS occurred underneath the mats,creating anoxic conditions. The carnivorous fish specÎes such as 0phicephalus strîatus,0phicephalus lucius, 0phicephalus micropeltes,0mpox bimaculatus and \,/al lagonia attu were abundant, indicating a compì icated food ,.ì... web and I ow eco I og i ca I p roduct i on . The open-water habitat represents the intermediate zone characterized by better r¡rater quality, abundance of bentho-planktonic forms and versatile ,,,, pìanktonic feeders such as Paralaubuca sp. and Cirrhinus micropeltes: .,,, Bung Boraped could be maintained at a highly productive level if much of ,,'.,:' the natural communìty were periodically destroyed before it reached the matura- tion stage. Water level manipulatîon in summer appears to be appropriate for maximîzing fish production. By this process the grass-covered habÌtat, which is most favourable for fish production, would be re-establ ished. ACKNO\,ILE DGHENTS 0n behalf of the NatÌonal lnland FÎshery Institute, Thaìland, the author wìshes to thank the canadÎan lnternational Develópment Agency, of the Freshwater lnstitute, Winnipeg, l,lanitoba and the Department possible' Zoology at the university of Manitoba for making this research to his suPer- . The authoF wishes to exPress'hîs deep apprecÎation visor,DF.R.H.'Green,forhÌsencouragementandsuPportduringthe and criticism inception of thìs research and for hîs valuabìe suggestions and Dr' throughout the work. Thanks to Dr. C.C. Lindsey, DF' K' Patalas helpful l.W. Dickson who served as thesis committee members for their crltlclsm. Theauthoris.gratefuìtoMr.V.Varigul,theDirectorofthe National lnland Fishery lnstitute, Thai land, under whose authority to research in ThaÌland was carried out. Gratitude is also extended Dr. G.H. Lawìer the Director-General of the h/estern Region, Fisheries work in and Harine service, Environment Canada, under whose authority Canada w¿s done. of The author wishes to grateful ly acknowledge the contribution Hr. v. BoonyaratplÎn, Head of the Nakhon sawan Fishery station, who the prôvided accommodatt'on, tfansPortation and hospital ity throughout study period. Thanks are extended to Hr' S' Chareonpong' Mr' P' Siritantrapon and Mr. T. Vasupital< for their invaluable fieìd assistance the soÎl and thro.ughout this study. A special thanks to the staff of laboratory Water Anaìysis Unit, Chemistry Agficultural Division, for H'K' assistance on soi ì analysis, Apprecîation is also extended to Hs' Friesen for critÎcally editing the manuscript' vl Last, but by no mean least, sincere grat¡tude is extended to my wife, Thanya, and my two ìittle sons¡ PÎnsai and Pinsuk who received far less than their share of attention during the work. Their strength dur Io.ng absences f rom Thai land were a constant ':::':'::::.:::, and understand ing ing .my ,,,.:,r,,i:;, inspiration to me. i:J f:.- 1.:-lIì. ;':;.::.1 :.r i - Ît.l 1 TABLE OF CO}¡TEI{TS PAGE iii ABSTRACÏ --- v ACKNOWLEDGIIENTS ------víii LIST OF TABLES xviii LIST OF FIGURES 1 INTRODUCTION ----- 6 MATERIALS AND METHODS ------30 RESULTS 30 lJa te r 40 Sed i ment 54 macrophytes ------: ------Aquatic -- 69 Invertebrates associated with aquatic macrophytes to Benth i c fauna 103 abundance -- Fish relative LLl Fish stomach contents 140 D ¡ SCUSS I ON ----- *:îï:"::-::::::l:::-::-:::::l::-::-:1:-::::::::::-- , 140 Techniquetorestorethereservoìrproductivity--_- 155 l. Water level maniPÚlation 155 of continuous water cover on a 2- Establ ishment l-58 grass-covered hab i tat 165 L ITERATURE C ITED vt | | LI ST OF TABLES TABLE PAG E | . Physical and chemical properties for oPen-water -;:::.:_.:' .l968-1975. region Ìn Bung Boraped, ìB 2. AquatÌc macrophytes found in Bung Boraped Reservoir, tglu-1975. l9 3. Gastropoda found in Bung Boraped Reservoir, 197\- 1975. z2 4. Pelecypoda found in Bung Boraped Reservoir, 197\- 1975. 23 5. Fish fauna found in Bung Boraped Reservoir, 197\- 2tl 1975. 6. Fish landing statisticsfor Bung Boraped Reservoir, 29 1965-1975. 7. The nutrient elements and major ions in water samples from the Grass Area (a). 37 8. The nutrient elements and major ions in water samples 3B from the Weed Area (c). 'g. The nutrient elements and major ions in water sampìes 39 f rom the Open Ì./ater Area (D) . 10. Analysis of variance for organic matter anÐng the the Grass Area (g) , the t'/eed Area (C) and the Open l^later Area (o) , excl udi ng the dry rnonths 4T llaY'A'nut t 1975 Il. Analysis of variance for Phosphorus among the IX PAGE TABLE the Grass Area (.9) , the. lJe.ed Area (c) and the Open Water Area (D), excludìng the dry months I f'laY-flugust 1975' 43 12. Ana lys is of variance for P.hosphorus between the Weed Area (C) and the Open Water Area (0) over the period'of l4 months, including the dry months May- August 1975. 43 13. An."lysis of variance for FÎne sand fraction (o.z-o.ooz mm) among the G.us Ar.u (g),. the l'Jeed Area (c) and the Open Water Area (0) ' excludinE the dry months MaY-August 1975. 45 14. Analysis of variance for Fine sand fraction (O.Z- Open 0.002 mm) betrveen the \'/eed . Area (C) and the Water Area (O) over the period of l4 months, I+5 incìudíng the dry months Hay-August 1975' 15. Analysis of variance for Silt fraction (O.Z-0.002 mm) among the Grass Area (g), the Weed Area (C) and the Open Water Area (O), excluding the dry months 46 Hay-August 1975. iì,, 16. Anaìysis of variance for si ìt fraction (o.oz-o.ooz i- --: -i .. mm) between the Weed Area (C) and the Open Water Ar.ea (O) ove r the per i od of ì 4 months , i ncl ud ing the dry months Hay-August 1975. :------17. The analysis of variance for Cìay fraction (ìess than g) .,;,,;,¡.,;,, 0. 002 mtn) among t he G ras s Area ( , :1.: l:ii:: :i: :,: -:l-,.:-'- rl, ---:* -'--,. -:-. Ì.-:.i'.',.--.1-1."."j. ..:.-.:ìilr:::,::; PAGE TABLE .The Weed Area (c) and the Open Water Area (p), excludi.ng the d¡y months Hay-Augusl 1975' ?FãF-F-FFF 49 The analysi's of variance for CIa.y fraction (less lB¡ :_,,.. than O.002 mm) between the Ueed Area (C) and the (O) per i od of I 4 months , open l^Iater Area over the . incIuding the dry months Hay-August 1975' .... 19. The mean and 95Î.u conf i dence ì ìmits of o.rganic i.,'. l :'1': Hatter, Phosphorus and Partlcìe sìze Distributîon 51 în soi I samp'le f rom the Grass'Area (n)' ------:------ 20. The mean and 952. conf i dence I i mi t s of 0.rgan i c Hatter,PhosphorusandParticleSizeDistribution in soi I sampìe f rom the \^/eed Area (C)' 52 2l - The mean and 95lz confi dence t i *i ts of O.rgan ic Hatter, phosphorrs ånd part i cì e si ze Di stri bution in soil samples from the Open Water Area (0)'' 53 :cover ZZ. The Inean and 95% conf idence I Ìmits of Percent ,,.:, Grass Area (g). ------of aquatic macrophytes in the 56 ' .: . .-' 23..Thernean-and9ü%confidencelirnÎtsofaquatîc.;'.:' 57 macrophytes in the Heed Area (C)..FF.FFFF---F--.FFF=F -LeérSia of variance on the dÌstribution of 24, finalysis :..i,,, t""' hexandra (Graminae) for the Grass Area (g) and 62 the'Weed Area (c). 25.AnalysisofúarianceonthedistributionofCynodon dactyìon (Graminae) for the'Grass Area (B) and 63 the lleed Area (C) . l.rri:: rì::: x¡ TABLE PAGE '26. Analysis of variance on the distribution of Fimbr'i'styl is mi I iaceae (Cyperaceae) for the Weed Area (C) from November lg7\ - Seprember lg7|. 63 27. 4n"lysìs of varÍance on the distributíon of lsachne . globosa (Graminae) for the Weed Area (C) from November 197la - September 1975. . 64 28. Analysis of variance for therdistributîon of CVperus. Cephalotes (Cyperaceae) for the Weed Area (C) f rom November 1974 - September 1975. --- 65 29" A.nalysis of variance for the distribution of Cyperus* di fformi s (Cyperaceae) ñ/eer the Grass Area (g) and the Weed Area (C) . -*-- 65 30.. Anaìysis of variance for the distribut'íon of C.oix 'êqùatiga . (Graminae) for the Grass Area (n) and .' - the l'leed Area (C) , F--FF-FÊF 31. The mean number and 95i¿ confidence I imÌts of inver.tebrates per one handfu I found associated wíth some major aquatic macrophytes wíthin. the Grass Afea (g), --F-Frç-Ê F--FF!--.---*^---- 72 32. The mean number and 952 confidence I îmit of invert-ebrates per one handful found associated with some major aquatìc macrophytes wÌthîn the l./eed Area FÈtsF*sq-r (C). ç-FF-FF.-F 73 xtl TABLE PAGE ' n: The percent f requency of occurrence of invertebrates . associated wÌth aquatic macrophytes in the Grass Area (g) :--- 74 34. The percent frequency of occurrence cif Ìnvertebrates associated wîth the aquatic macrophytes in the \'leed Area (C). ---:---- 75 35-:' The mean number and 951 conf idence ì imits of benthic organisms in each core sample from the Grass Area (e). ------!------: 80 36. The mean number and 952 confidence timits of benthic organîsms Ìn each core sample from the Weed Area (c). 81' 37. The mean number and 952 confidence I imits of benthic organisms in each core sample from the Open ly'ater Area (o). ------82 on the'abundanåe of 39, Th" a.naìysiç of Yêriánce Corbicul i'dae amo.ng the Grass'Area (g), the Weed Area (c) and the Open Water Area (O), excludÏng the d ry months May-¡Aug us t 1975 , 85 39. The analysis of varíance on the abundance of Corbicul ìdae between the Weed Area (C) and the Open lJater Area (O) over the per iod of l4 months, incÏuding the dry months Hay'Augu5¡ 1975- B5 )it t¡ TABLE PAGE 40. The anaìysis of variance on the abundance of Ampuìlaridae among the Grass Area (B), the l.leed Area (C) and the 0pen Water Area (O) , excìudïng.the dry months Hay-August 1975- 87 4t" The analysis of variance on the abundance of Ampuìlarîdaé between the Weed Area (C) and the Open Water Area (O) over'the period of l4 nnnths, including the dry months Hay-August 1975. 87 I+2. The anaì:ysis of variance. on the distribut ion of Planorbîdae among the Gråss Area (B), tlre \',eed Area (c) and the 0pen Water Area (o), excluding the dry months May-August 1975- 88, 43. The anaìysis of variance on the. abundance of 6 Ql.igochaeta.amo.ng the Grass Area (A), the l^Jeed Area (C) and the Open htater Area. (n) , excl udi.ng the dry months Hay-A.ugust 1975. rFFFF B9 44. The analysis of va.i"n.. on the abundance of 0ì.igochaeta. between the Weed Area (C) and.the'0pen Wa.ter Area (p) over the per iod of l4 months, includÌng the dry months Hay-fiugust 1975. 90 abundance of 45 The aÀalysis of variance on the (g) Paleoptera amo.ng the Grass Area ' the lJeed Area (L) and the Open l^Iater Area (o), excludi.ng the dry months Hay-August 1975. 9L xtv TABLE PAGE '46. The analysis of variance on the abundance of Trichoptera amo.ng the Grass Area (g), .'.,. the Heed Area (C), and the 0pen Wate, Ár"" (O), excluding the dry months Hay-August 1975. -----: 93 47. The analys.is of variance on the abundance of Coleoptera :..: . : . ',: ... among the Grass Area (g), the Weed Area (c) '...... :_: ,: : and the 0pen Uater Area (O) excì udÎ ng . , :,':,;;. ' the dry months Hay-August ÉlS. 'g4 - 48. The analysis of variance on the abundance of Col eoptera between the Weed Area (C) and the Ope.n Water Area (O) for over the period of l4 months, excìuding the dry months May-A.ugust 1975. - 95 49. The analysis of variance on the abundance of ' Hem[pte¡a amo.ng t he Gras s Area (g) , the Weed Area (C) and the Open Water Area (o) excl ud i months May-A.ugust 1975. 96 , ng the dry ..,_....',i1.,..., : ì_ 50. The analys Ìs of variance on the abundance of .",'.':,' 't t' ""- Hemiptera between thè Weed Area (C) and the Open lr,ater Area (0) over the pe¡iod.of lll ¡nonths, Íncluding the dry nronths Hay-August 1975. - 96 ¡.:::i:,: ::' 5l-. The analysis of v ariánce on the abundance of Di pt-eia amo_ng the Grass Area (B) , the l,leed Area (C) and the Open lJater Area (O), excludi.ng the dry months Hay-A.ugust 1975. ---:---*-' 98 TABLE PAGE 52. The analysis of variance on the abundance of Diptera between the l,/eed Area (C) and the 0pen Uater Area (O) over the period'of l4 months, i nc I ud i.ng the dry months Hay-Augus t 1975- - 98 53- The analysis of variance on the abundance of Chaoborinae among the Grass Area (g), the l^feed Area (C) and the Open Water Area (O), excludi.ng the dry rnonths Hay-August 1975..------99 . The anal'ysis of variance on the ãbundance of Chaoborinae between the Weed Area (C) and the 0pen Water Area (O) over the period of 14 nonths, including the dry months May-Auiust 1975 100 55. - The analysis of variance on the abundanc, of Chironomidae among the Grass Area (A), 'ì the Weed Area (C) and the Open Water Area (O), ,,:.., ::': ' exclud i n9 the dry months Hay-A.ugust 1975., 101 :: : 56. The analysis of variance on the abundance of '': Chi ronomi dae the Weed Area (C) and the .between Open Water Area (o) over the period of l4 months, '¡ççeç-¡--'ç inc I ud [.ng the d¡y ¡non ths Hay'A.ugus t 1975 ; LOz :':.-.,i',,. 57. Ferce¡rt specíes composition of fj-sh in Bung Boraped, ocrober L974 - 1975. -----i------. .1Ú5 . {.:-: l -rr:-,^j.,"::.:,",. .:.:;r.: i: .: i-r: -:,_ ?,i: -t:ì:i ì I ì:l::jlt:: t ::': | :::: ::.-: xvl TABLE : PAGE 58. The mean we.ight of fish caught by a set of exper imenta l. g i I I nets from the Grass Area (a), the l^/eed Area (C) and the Open l{ater Area (D). 111 59. The mean weight of fish caught by a set of experimental gill nets by each mesh si2e from tne Grass Area (g) , the t'leed Area (c) and the Open \tater Area (D). ---. LT? 6Q' The total numbe¡ of fish ca.ught by Electro Fishi.ng (15 minutes run) and species conPosition from the 113 Grass Area (B) and Weed Area (c), -ÊÈF-s-F- 61. The total number of fish caught by the exPerimentaì 9i I ì nets and species compos ition (c) f rom the-.Grass Area (B) , the Heed Area and the Qpen l.fa tef Afea (O) . ç- GZ. The anaìysis of varián." for the fish caught by of three different mesh sizes , gill nets composed (3 .t, 5 cm and B cm) from tl-re Grass Area (g), ra (C) and the Open Water Area (o) over the period of l0 months. 115 63. The a.naìVsis of variance for the fish ca.ught by gill nets composed of thrèe different mesh sizes (3.t, 5 cm and B cm) between the Weed Area (c)'. xvii TABLE PAGE and the 0pen ïJater Area (O) over the period of l4 months, including the dry months May-August 1975. 1-l-6 / 64. The mean percent and 95"'( conf idence I imit of : - (g).,^l contents in fish caught from the.Grass Area L34 65. The mean percent and 952 confîdence limits of contents in fish caught from the tleed Area (C). L35 ' 60. The mean O.r".na and 95"¿ conf idence t ímîts of the major food contents in fish stomach from the ,i.GrassArea(B),over:tÍme"F------lFFf|.-F-.l- 67. . The mean pé¡cent and 95% contid.ence limîts of the' -' ' major food contents in fish stomach from the'.t from : 1?7 | t^leedArea(c)over.time.-ÈF--tsF--FÞ-rE-F--FF-?îeF-- , ,'68., .The mean percent of stomach fullness and 95% ^t cont r dence t ími ts ovef -24 hours feed ing : lfriod 6i. The'mean Percent and 95"Á conf Ìdence I imits of the . ; major food.contents in stomachs of fish În 24 I hours feeding period 139 70. The.s_pecies composi tion by number of f îsh in Bung nor"pua,.from landing statistics !n 1969, 1971, 1973 and 1975" 153 i 'h-- i:-::-l xv¡ | | LIST OF FIGURES F I GURE PAG E I . l4ap of Tha i land showing si te of Bung Boraped Reservo i r . 2. fiap of Bung Boraped ReservoÌ r, Nakhon Sawan Province, Thai land. 3, Water level fluctuation and monthly rainfall in Bung Boraped Reservoir, November 1974 - December 1975. L4 4. Location and experimental design of study areas A, B, C and D. 5. Stands of float¡ng vegetations in area C. ----:------L6 6. Diagram showing the experimental gi I I net and the sett¡ng sites. L7 7. The major ions in water samples from the Grass Area (n), the h/eed Area (C) and the Open k/ater Area (O) .- 35 B. The n utrient elements in water samples from the Grass Area (g), the V/eed Area (C) and the Open Water Area (o) . 36 9. Organic matter, Phosphorus and Particle Size Distribution of soiì sediment in the Grass Area (g), the Weed Area (C) and the Open \,/ater Area (D). 50 10. The distributions of major aquatic macrophytes in the Grass Area (B) and the Weed Area (C). 55 I l. The development pattern of some benthic organisms witfr respect to time in the Grass Area (g), the iat,:':': xix FIGI]RE PAGE lleed rea (C) and the Open trlater Area (D) . B3 L2. The contents ín stomachs of fish from the Grass Area (g) and the l{eed Area (C) . ---- L32 13. The diel feeding as expressed in percent of fish stomach ful I ness 133 ; '.::.ti:.:<.1 I INTRODUCTION Bung Boraped covers 208 km2 in area and is the oldest reservoir in Thailand. lt was created in 1930 for use as a water source for irrigation and as a f ish sanctuary. 0riginaì ly, Bung Boraped was to be f ished in- ::,,, :,,:. :;':. :..::: f requently, or not at al l. However, as the demand for f ish protein increased, .: portions of the reservoir were opened to fishermen. An individual catch limit was enforced. Bung Boraped has been recognized as one of the most potentially productive areas in central Thai land. I t had played a significant role in providing 50-80% of the animal protein requirements for the people of the region, but the production decl ined in 1959. ln the summer of 1959 the Fishery Department decided to drain the reservoir for I month. After refi I I ing, fish production was restored and fishing catches remained high for more than 5 years. lrr 1972 the reservoîr had deteriorated, having more than half of its surface area covered with noxious plants. Torgme and Chatmara¡ (1971) reported plants such as Eichornia'crassipes, Coix aquatica and Sulvinia cucul l3ta. ln some areas, black reducing sediment had been deposited on the shoreline, subsequently causing increased water temperatures. Plegchavee (lgZ¡) reported thlt fish production had decreased and the fish harvest. t^ras lower than in ear years. f!1_reservoir was again drained during the dry season of 1972:for one and a half months, exçept for the old stream channels and certain deep areas of the reservoir r"¡hich were prevented from draining by a mud bar across the outlet. In the interval before the monsoon rains refil led the reservoir, natural grasses became establ ished in most of the drained areas. After refi I I ing, this grassy habitat became excellent protective cover and a good substrate for benthic ,"" organisms, apparently ìeading to increased food production. This cover formed a good spawning ground for fish populations' (t-þ In this. Fluctuating water level'ecosystem 0dum (1971) productivity is high,when the reservoir is kept at an early succession ,; ,..; - I :rt.t:::: stage. Odum states that man does not recognize the irnportance of recurrent natural change in-water level. In his opinion this fluctuation, rvhich has been commonly used in rice and fish culturing for centuries, is the analogue of the natural march of the intertidal ecosystem. lf this method of nutrient addition could be made easily reproducible, a large scale fish production could be developed thus providing a protein supplement for the protein-deficient countries of the world. A serious interest in reservoir fishery management in Thaiìand began less than 30 years ago, although pond fish culture has been practiced for thousands of years, Fish systematïcs and distribution have been studied by workers such Srnith (1945), Suvattii (.|950) and Thiemedh (1g66). Hydrobiological research has increased in the ìast few years. Ecology, I imnoìogy and fish populations have been studied in the .l970 form of exploratory surveys (S¡dthimunka et al. 1968, and 1972). Fish feeding and spawni-ng were investigated by several workers, such as Mizuno and Mori (1970), Potipitak (1970) and Pholprasith (1974)' The need for a conservation-oriented program of fisheries research and management has been increasingly recognized. V/ater level manipulation (\,lood, 1950; Bennett, 1967 Jenkins, 1970 and Bhukasawan, 1973) was tested in Bung Boraped in 1972 in an attempt to control the aquatic weeds .l960; (Quenerstedt, 1958, Runstrom, Lantz et al., 1964 and Junk, 1973). .. _.ì ri. 1.; ¡.1;;t As a consequence, the reservoir productivity and fish ìanding statist¡c : increased (anonymous.l973 and 1975). A return of the reservoir to an early stage of succession (Penfound and Schneidau, ì945; Regier, APPìegate and Ryder, 1967; Margalef , l96t{; odum, l97l and Regier and He'nderson, 1973 , :,:::: was believed to be the responsibìe factor. Aìthough the results of this .".',.',-.' type of manipulation are qui te evident, the impl ications, aPPì ications and management techniques are not thóroughìy understood ...: .,. In November lg7\, under .the Columbo Pìan/NlFl Project, co-oPerative ,,,',..: research was begun by the University of Hanitoba, the Department of Fisheries ':::,r: of rhaiìand. The ''ì''t':' and Marine service of ,canada and rhe Fishery Department initial objective was to obtain information about the mechanisms invql.Ved in the nutrient cycìe, the effect of vrater level variation, effects on the food chain and the interreìationship between flora and fauna' especiaìly theadvanta9eofgraSSeSoVerfloatingrveedsforìocaìfishspecies.|t is hoped that this informationowi ì I help to improve management and ìead to higher fish Production This thesis describes characteristics of the grassy habitat, weed are presented on f ish fauna , '.;:'','.,,.',",';.; covered habi tats and open water habitat. Data . ":'.'.: f auna water 'and ' l''."". stomach contentS, benthos, vegetation and associated ' "-'.-,.:..,:,'..: ''. sediment anaìYses Figure l. Map of Thailand showing site of Bung Boraped Reservoír. :,1, 11 l': ; .:.1:l :.: ,.'-:: ::; ' I l.':; : :": i..¡i-t-.::::ì. Figure 2. l'Íap of Bung Boraped Reservoir, Nakhon Sawan Province, Thai land. RIMENTAL SITE AKHON SAWAN FISHERY STATION -OUTLETOL GATE INLET o12 (r¡u) it', ,f :ì'll: l'i,l ', .:,,,,,.1 ìt," ;i il MATER¡ALS AND METHODS Description of the StudY Areas The Bung BoraPed Reservoi r At the confluence of the Ping and Nan Rivers, which form the Chao ": "t't 't' ' phyo River after their junction at Paknampo in Nakhon Sawan Province "":" (l5o ¡t, | ies Boraped Swamp which is wel I known in Thailand 50' (Figure l) 1!e l00o lO, E; 2\ n. above mean sea level)o At periods of high water swamp a big lake of 640 km2 area (Anonymous, level , the whole Boraped formed -l.:..,:,. .1 1956) which was used by f ish for spawning. ln the dry season many smal I ;r..,.. bushes sw_ampy depressions remained in a plain which wasovergroþ,n with and grasses. Following the advice of Dr..H. M. Smitfr who was the advisor to the Fishery Department at the time, a dam was built between 1926 and 1930. This transformed part of the swamp ¡nto a lake of area 208 km2 area which has been known as Bung Boraped (Luther and Rzaska, l97l). As the terrain is flat, the lake area changes extensively with water level fluctuations. The dam wall serves in places as a railway embankment. There are several outflows and weirs at Klong Boraped, leading previous main outlet of the swamp into a winding canal which represents the ,,.,i,',,,'ì .'. . '. '. ': area into the Nan stream. A Fishery Department Station, Nakhon Sawan ',, '::: :: Fishery Station, si tuated at the weir is concerned with investigating the problems relating to fishery biology in the lake' There are approximately 30,000 people I iving around the lake with :.,.,, an average of 6 persons per family. The majority of these people gain ": intensive their I ivel ihoods from both farming and fishing. Due to the fishlrV activity in Bung Bo:-aped the per capita income of people ¡s higher tlan the average per capita íncome il ,his area ' I iving of people ín other rural areas. The people .around ,.,.. i:: i.t: 7 the lake obtain food from rice cultivation, fishing, cattle raising and lotus propagation. Bung Boraped can be morphologicaly dívided into 3 areas (r¡gu re 2)i (l) the outflow area near the Fishery Station which is studded with several flat islands occupied largely by terrestrial and semi-aquatic macrophytes, (2) the central area which is a large area of open water, and (3) the inflow area which is also characterized by the presence of small islands, merging into a system of channels which during the dry season end in rice fields. At the period of high water levels, September-December, the entire ',.ì', low area is flooded and is ¡nterconnected with the lake in many places. l'/hen the water level fal ls, the lake is again isolated f rom the surrounding water bodies. The drop in water level of 2-3 m which occurs before the flooding period is primarily due to evaporation. At low water levels the lakeisanaVerageof3-4mdeep,withsomedepressionsandchanneìSupto 6 m deep in areas formerly occupied by ponds and overflows. The open water is dark brown in color and sometimes quite muddy. The Secchi disc readings range f rorn 0.60 to l.B0 m and the pH values to 6.6 to 7.9. The 0, content of ,.,,.,,i the entire lake is fairly high, 3.0 - 8.0 ppm, because of the frequent '"' mixing of the water in the monsoon season. The eìectric conductivity range ,',,r'., from 109 to ll0 ¡tnho/cn (fable l). The average annual rainfall in this area is about 1250 mm (fisure 3). The average monthly temperatures range from l2.Ooc in December to 34.ooc in May. ,,,,.i, There are luxurious stands of aquatic macrophytes in Bung Boraped; 40 species from 2l famil ies. Among the floating plants co¡x aquatica, lsachne globosa, Leersia hg."nll", Eichornia crassipes and salvinia cucullata are the most common. The submerged plants Hydrilìa ysr_t_tcglrelq ) ..; ,:l CeratophylumdemerSumandUtriculariaflexuosaoccurmostoftheyearin the whole area, but only in small quantities (faUle 2). Annelids, snails and insect larvae such as Ephemeroptera, Diptera, Coleoptera' etc. are the dominant groups of benthos in the lake basin. During the study period species of Gastropoda and ll species of Pelecypoda were observed (table l0 ,,.1 .;,,.,, 3 and 4). There are l4B species of fish in Bung Boraped and among these the Notopteridae, Cyprinidae, S¡luridae, Schilbeidae, 0Phicephal idae and Eleotridae are the most important groups (faUle 5). According to the '''t',;,, stat¡st¡cal reports from the Nakhon Sawan Fishery Station (1g76)r723,048 ,|,081,665 wi.th 86z,\\5 kg in 1965 and kg. of f ish were landed in 1975 compared "":,' kg in 1972 when fishing was intensified because of the draining manipula- rion (raUle 6). 0f 723,048 kg of fish landed in 1975,184,306 kg was Qphicephalus, 113,728 kg Qstiochilus, \5,978 kg Pristolepis, and 42,656 kg Puntius. The study areas Three different types of habitat within the lake outflow region wereselecte,ilforstudyanddesignatedasthegrasshabitat,theweed-covered habitat and the open water habitat. The grass habitat was located on the shelf of the shoreline with some extension into the water. The habitat represented the early stage of succession and wouìd simulate some character istics of the grass-covered area that was establ ished duri ng the water-level manipuiation in 1972. The weed-covered habitat served as the trânsition zone between the grass and the open lvater and represented the deeper second stage of succession. The open water habitat was located in the C' and D part of the lake. Three study areas clesìgnated as B' were located within those three habitats for experimental purposes (f¡gure 4). Ì:::íi:):,::i:: j'i::ir Each experimental area r{as a square 50 m x 50 m and can be described as fol I ows: I (l) Area B is situated within the grass habîtat. The average water depth is around one meter during the flood períod when the water surface of the reservoir is 23.8 m above mean sea level. During the summer months area B ...: :t¡-,.¡t,.::¡,-'11. r' dries out. The water during flooding is brownish with low transparency. Three ::r:'1.:j'ir::r,: major kinds of grasses grow in this habitat: Leersia hexandra, Hymenachne pseudoiterum and Cynodon dactylon. During the dry season (Aprit to July) ', the level drops the area dries, and the grass stays short and flat to "".' water .j:_:1 ...-..;: - . a .: .r_-: :,. .. start to grow as the water rises slowly. Growth keeps tne grass tops above the water surface. Most of these grasses remain alive in water for 2-3 months then die as the water recedes. They decompose and release nutrients back , "nd i into the reservoir. The B area represents the natural condition of the i grassy habitat and simulates some characteristics of the water-covered grassy I areas which were created during the water-level manipulation in 1972. (2) Area C is located in å. floating vegetation stands. The depth ranges from three meters in the flood season to one meter ìn the dry season. These floating stands of vegetation often show zonation. The inner regÎon is occupied by Phragmites karka and Coix aquatica which are sometimes rooted in the substrate. Beyond this zone is a floating stretch of lsachne globosa and Nel umbo nuci fera. 0n the t: :-:.a t0 outer edge is a wide belt of Eichornia crassipes, Salvinia cucul lgta and Cvperus cephalotes (f¡gure 5). Area C was enclosed by a frame of bamboo to protect the vegetation from prevai I ing winds. Two strips cleared of weecls þ/ere constructed at each side of the area for gill nett¡ng (Figure 6). (3) Area D ìs in the open water at approxÌmately one kilometer from the lake shore. The depth of the area ranges from 2.0 to 6.0 m. The transparency is approximately 0.5 - 1.5 m. The dissolved oxygen was found to be at fairly high levels throughout the water depth because of strong turbulence in the oPen area Water quality The investigation of brater quality in the four designated areas was ,conducted between November 1974 and December 1975 at monthly intervals. The water samples were taken by means of a 1000 cc Van Dorn wêter sampler. Dissolved oxygen, carbon dioxide, aìkal inity, hardness, chloride, sulphate and phosphare were measured with a Hach Lab Kit (cR-oR-rl cat. No. 1200-03) and were expressed as mg/I. Dissolved solîds were measured with a conducti- vity meter (tl,t¡,t, Model Mc-l). Hydrogen-ion content was determined with a Beckman pocket pH meter. A Secchi disc was used to measure transparency. I^Jater and air temper a tu res r/'/ere recorded . Sed iment character istics A multiple corer described by Hamilton et al (tgZO) was used to obtain samples for soil analysis. Each drop yíelds four 4.7 cn diameter uru") cores. A series of six multiple corer drops was taken at 07.3 "r2 each time and for each area of study, and empt¡ed into plastic bags' ì::::;: '''':: t:" -' |'.{. "..'.'. tl -: l.:f.: and dried at room ., The samples were then brought to the laboratory :'.'.";.' temperature. each multiple corer drop a total of four core samples t^rere obtained but only 2-core samples were used for soil anaìys¡s' the remainder being used for the benthos study. The drop number and core number of each particular area were recorded so that variation among repl ícates ,- ,,,.:'.: ,,.t,:.t-l,t¡.r:t: ,t: could be determined. The organic matter, expressed aS percentage' was determined by the llalkley and Black (lg¡4) method. The Jackson method No. vi (l960)wasusedtoana|ysephosphorusandwasexpressedinppnrParticle ì_,'t,',t, , ,t, ,t-, size distribution was also determined by the sieving and pÌpetting method "".:'::.: (Oewis and Freitas, 1970). Fol lowing the International System soil was 't¡,,.''..¡..ì¡., - . -- -' . l separated into 3 major sizes; f Ìne sand (O.Z-0.02 mm), silt (0.02-0.002 mm) and clay (less than 0.002 mm). The data were expressed as percentages of weight (Dewis and Freites, l97O). A total of 584 samples were collected from November, 197\ to December 1975. A two-way analysis of variance (randomized complete block design) was used to test for significant differences among ar-eas and times for the amount of phosphate and,-organic matter, and the:part.îcle s ize distribution.l The 95% conf idence I imits were calculated for eacir rÏìêêll¡ ,,;¡,1'.,,¡,,,.,..,, ' In this and all further analyses of varíance a probabílity of ::i::::i::': | - t'no ..,.-, ...-,.,- (O.OS is taken as the criÈeríon for rejection of the null hypothesis of ,,,'¡. ',:,,r',1' difference among comparisons. å""tft¡. ..9"" i* The benthos were sampled with the multiple corer (Hamilton, l97O) and were washed through the U.S. Standard Sieve Number 35 (500 micron). Alì organisms were preserved in 70% alcohol unti I identification. In the laboratory the sample from each core lvas emptied into a I.S.C. Pretri..and examined agaínst a white background l2 us¡ng a dissecting microscope. The organisms were classified into order and f ami ly levels. After the identif ication and quantitat ive study the specimens were grouped and again þreserved in 707, alcohol with organisms of the same group. The wet weight was ìater determîned. The ìn(x + l) t raisformat ion was u sed f or dens i t i es- The tv¡;r-way anaì ys i s of variance (randomized complete block design) was used to test for significant differences among areas and times for benthic organism densities. The 957. confidence limits were caìcuìated for each mean. Aquatic macrophytes and associated fauna A ìxl m rvooden frame \^ras used to sample the vegetation in areas B and C. A series of 6 random throws was made in each area. Each species of vegetation that appeared inside the frame was necorded as percent cover. A handfuì of each species of vegetation which exceeded 25"1' cover was collected' and the associated species of invertebrates present were determined.' The study was undertaken f rom November ì974 untiì the weeds were s\^/ept away by high water in 0ctober 1975. plant distribution data- The arsin {$6- transformation was used for The ln (totaì + l) transformatÌon was used for numbers of invertebrates associated with aquatic plants, The tvro-way anaìysis of variance (randomized compìeted b lock design) was used to test for s ignifi- cant differences among areas and times for the distribution of aquatic plants. The 95% confidence I imi ts were calculated for eacl¡ mean. F i sh re I ative abundance Each set of nyìon gill nets consisted of a belt of three different - -' - - '-" -lr:;::ì:::: i''"'::''' r3 were two sets mesh sizes; 3,5, and I cm stretched mesh (f¡gure 6). There of gill nets for each area and for two consecutive nights. The nets b'ere set perpendicular to the shore at lB00 hrs and were removed at approxinrately 0600 hrs. Each individual fish retrieved was identified. Total length and weiglrt were determined and separately recorded for each gill net mesh size' A factorial analysis of variance was used to test for significant differences among areas and times for the fish biomass caught by each unit of experimental mean' gill nets. The 95% conf idence I imits \4/ere calcul'ated for each F¡s@ """"' Because of regurgitation and fast digestion by fish in the high tropical temperatures, an electrofishing device was chosen to collect fish forstomachcontentanalysis.TwolocationsadjacenttothegraSSyhabitat andrveed-coveredhabitatwerefishedfortwoconSecutivenightseach.After capture fish were identified, weighed and measured. The body wal ls were opened and stomachs plus contents h/ere removed and placed in vials contain- ing l0% formal in unti I further analysis. Percent frequency for each type of food organism of occurrence by volume was determined ',,,;.,,,, ( determ i ned by compar ison to an obj ect consumed fo I t, I 971 ) . Vol umes were ,,. t"t:' of known voìume (Larimore , lgsn. . During September 1974, and March, August and December 1975, fish feeding periodicity'was studied. The electrof ishing device was used' Fish 0800 Each were col lected at 1200, l600, 2000, 2400, 0400 and hours' '..'.. lecting individual specimen was identified and recorded, according to its col time. The index of stomach ful Iness was determined by volumetric displacement' Figure l. Water level fluctuation and monthly rainfal I in Bung Boraped Reservoir, November 1974 ' December 1975. t4 TOTAL RAINFALL WATER LEVEL (mm) (meter obove meon seo level ) 26.4 ^ i\i'\ 25.5 í \ 450 ,'ì t I I t I I 400 I 387.9 I ,' I 350 in ì z+.s \- 24.3 300 250 200 r50 roo 50 NOV DEC JAN FEB MAR APR MAY .JUN .JUL AGU SEP OCT NOV DEC 74 75 Figure 4. Location and experimented design of study areas B, C and D. t5 SHORE Grass 5Om Grossy Hobilof I +50m - Weed Covered Hobitot Weeds Open oreo Open Woler Hobitof Figure 5. Stands of floating vegetation in Area C' Phrogmites korko Nelumbo nucifero Coix oquotico lsochne globoso Eichornio crossipes Solvinio cuculloto.:l Cyperus cepholotoes or C. difformis or Fimbristylis mi llioceoe Nym phoeo lotus -'ì =-¿ É-::- --:- o\ .. ".' t. ; .,: i; I 1.:: ì.: i.:::,:';,: :i:. t,i ,:. ì.i,iìi..i Figure 6. Diagram showing the experimental gill net and the sett¡ng sites. I l.Om 3 cm mesh size I u cm mesh size I t cm mesh size I þ- 5 m ---+l+---Srn | .------+ lS m-41*--5m SHORE NET NËT NO.l NO.z {UIQ Table l. Physical and chemical properties of open water region in Bung Boraped, l968-1975. :t:kuk l 968'" t970 197 t 1973' 1974-1975 Transpa rency 45-90 | 5-60 45- r 00 | 5-60 60- r B0 (cm) Oxygen 4.0-7 .0 2.5-12.5 3.5-7 .5 3.0-9.0 3.0-8.0 (mgll ) Carbon D ioxide 3.5-9.5 4.0-24 .0 6 .o-22.0 (mgll ) pH 7 .3-7 .7 7 .o-7 .8 9.3-7 .7 6.8-7 .B 6.6-7 .8 Alkalinity 68- I l6 Bo- r 50 40-90 (mg/ I ) Conductivity 135-l5l r r0-r40 r0g-r70 (ruho/cm). .L ^ Mizuno and Mori, 1970. Nimsombon and Tongme, 1970. Junk, 1973. 5UnKAgUl,' lq7?,rr¿. .;:;:l r9 Table 2. Aquatic macrophytes found in Bung Boraped Reservoir tg74 - 1975.x Fami r ly Polygonaceae j:l', ' :.t,, Polygonum tomentosum tr¡ I I d Fami ly Nymphaceae Nymphaea I otus l^/¡ I ld Nelumbo nucifera Gaertn Fami ly Onagraceae ;:;: ,.: ; '.: : .t:...: Juss i aea repens L i nn . Juss i aea sp. Fami ly Trapaceae Trapa bispinosa (Roxb) Trapa quadrispinosa Roxb Family Pontederiaceae Pistia stratiotes Li nn. Fi¿I'ornTã_crass i Þes So tm frõõffii-a'/aglnaT¡-s (Burn. .f) prest. Fami ly Cyperaceae Scirpus grossus Linn. Fimbristylis mil iaceae Linn. Cyperus difformis Linn. Cyperus platystyl is Linn. Cyperus odoratus Li nn. Cyperus corymbosus Rottb. Cyperus cephalotes Fami ly Hydrochar i taceae Harsil ia crenata Presl. Fami ly Ceratophyl laceae Salvinia cucuì lata Roxb ex Bory Fami ly Hydrochari taceae Hydri I la verticeì lara (Linn. f) Royle 20 Fami ly Ceratophyl laceae CerátophVl lum demersum Linn. Fami ly Lentibular iaceae Ultricularía flexuosa Linn. Ultricularia aurea Lour Fami ly Grami neae ffiw.Echinocloa colonum (Linn.) t_¡n¡<. @b. lperqta-EyìTndr ica (1. ) p. Beaur. Eñarum- spõltane-urn L i nn. Fiã'roryza ariTãE-Tnetz) Nus. ex \,/eight et Aru. e¡ragmltes-Earira TRetz.) rrin ex Stewd ¡ (rrrunl odtze. Cynodon dactylon ffianacfi;; ps euã-o i terum Family Convolvulaceae I Þom ia aquât ica Forsk. Family Leguminoceae 1r Neptgnia oleraceae Lour. Sal ix tetrasperma Fami ly Amaranthaceae Alternanthera sessi I is (f.) R.B. ex R. t S. Fami ly Araceae Colocasia esculenta (1.) Schoot Fami ly Compos i tae Bìumea cha rkei H. K. F. Fami ly Aoanthoaceae H_ydrophyl la g.reg!g. (gurm) Hochr. Fami ly Asclepiddaceae 0xystelma esculentum R Br. i:ì:::". i. '-. 2l Fami ly Therlypteridaceae - Thelypteris gongylodes (Scn tufrr.) Smal I Femily Commelinaceae ,1..,1. Commel ina clavata clarke. ldentifications were made by the Aquatic Taxonomy Unit, l,lational Inland Fishery Insti tute¡ Tha iland. Ì,.'.::::.-.: -..:L 22 & Table 3. Gastropoda found in Bung Boraped Reservoir, 1974-1975." Fami Iy Viviparidae ldiopoma ingal ls iana (lea) ïT¡ opalubiñ-ffimma (Ma rtens) @ Mekong i a sp. Family Ampullaridae Pi la pol i ta (Deshayes) Pila sp. Fami ly Th iar idae Brotia variabil is (Benson) CTea ¡an¿or'îarn lyiãblTTe et le Mesle) Fami ly Lymnadidae Lymnaea luteoìa lamarck Fami ly Planorbidae Indoplanorbis exustus (Deshayes) ¡k ldentif ications were made by the Aquatic Taxonomy Unit, ,:.r:.:': .,a ., .',,r, i.., National lnland Fishery Institute, Thailand. :. 23 tau\te 4. Pelecypoda found in Bung Boraped Reservoir, 197\-1975." Fami ly Myt i I idae Limnoperna siamensi s (Morolet) Fami ly Carbicul idae Corbicula siamensis (Prashad) ffi¡culã mlãGna Prime Fami ly Margari ti feridae Pseudon inosculatis cambodiensis (Ret¡t) Fami ly tJn ion idae Limnoscarpha delaportei (Crosse e Fisher) Ey rl opãl=-T-'r aTãEG-ffi-pson rñiìens iñÇi-iîE-nus (lea ) eirvsmø superbu;--(lea) F--¡I s¡rvoconðñã ex ¡ I is Conpren (Martens) Gñtraãens semiãõratus (Horelet) C-Tusïîca 1f.ã- õ. îumî3u-l us (tea) -s""çi*fl* (t-ea) The identification was done by the Aquatic Taxonomy Unit, National I nland Fi shery I nsti tute, Thailand. LA,1, Table 5. Fish fauna found in Bung Boraped Reservoir, lg7\. lg75.x Fami ly Dasyat idae Dasyatis bleekeri (elyth) Fami ly Clupeidae Clúpeoides hypselosoma (gleeker) Fami ly Engraul idae Coi I ia macrognathos (eleeker) STlpTnnalËÏanoc¡r ¡ r (el eeker) l- ta-rvJcuv. anãTl . ) l=ycotfrr ¡ssa crocod i I us (gleeker) Fami ly Notopteridae llotopterus chitala (ttami lton) @tas) Fami ly Mastocembel idae Macrognathus aculeatus (gloch) .. l,4astocembel us armatus armatus GÚnther n.Ecun'rc1 nctul-H'ora E-. Genlãôaster rowler Fami ly Flutidae Fluta alba (Zu¡ew) Fami ly Cyprinidae Oxygaster s iamens i s (Gijnther) @eeker) Macrocñ-IFi chThys macrochi rus (cuv. and Val.) ffiõîlffiI- @ P. harmandi Sauvage õu lEõÞl-ïamens is (uora) Esomus meta I I i cus Ah I @ura Bleeker L. bleekeri Steindachner FasUorãl'õraÞetensis H. M. Smith @ker) R. retrodorsal is, new species ñ'. rr-60ra ]HãmIl ton) IepEõarEõs hoeveni i (Bleeker) 25 Sikukia stejnegeri H. H. Smith ¡lVstaco t eucus ch i I op!ef u: Fowl er Harnpala dispa H. M. Smith Frnacrolepi¿ota van Hasselt Tatlõcarpiõãm'ens Ì s Bou lenger Cvclocheilichthys apogon (Çuv. and val', C. enoplos (Bleeker) FroEnr6us iul I ieni Sauvage ffiiT¡us-pilcfi-at rr H. M. smi th Cirrhinus microlePis Sauvage iffiiTÌãnl-êtr,/ase Funffiart ipentazona (Fowl er) qonionotus (Bleeker) P. + P. ãTîFlE-ntner) tr. scñwanenfeldi i (Bleeker) P. orphoides (Cuv. and va I . J Puntiopl ites protlez_ysron \b/nr leeKer/t \ Balantiochei ìos melanopterus (öleçKerJ Thvnn¡chthvs thvnnoides (bleeKer/ 0steochi lus melanopleura (ö leeKer/ 0. hasseltii (Cuv. and Val.) õ-. ãuosij-jma Fowler õ. vi-tlatus-(cuv. and Val.) : Fowler [. -;---lpilopleura ,^ \ Labiobarbus burmanicus (DaYJ L. kuhlii (Cuv. and val.l f. TÏirea-tu s (sauvage) l-. lpiTõpleura (H. M. Smith) f. leptocñffis (Van tlasselt) runca tu s (Bleeker) ÃmulJlTvrrcrricFfhysffiITuv.ãü.v:t.ì t Moru I i us chrysophekad ¡on (E I eeKer / G'6õ]ñofficies F¡cõlor H. M. Smith t- . ñrunenTi-s H. H. Sm i th L. ervthrurus Fowler carra tae-nlãfa H. M. Smi th FssoffilTF-oblongus (Cuv. and Val.) C. Reba (Hamiìton) ,"r,r;tnocheil idae eyi¡nåche¡ lus aymonieri (Ti rant) Family Cob¡tidae Botia lucas-bahi Fowler _-_-_--?_^'' B. hymenophysa (b I eeKery B. horae H. M. Smith E. rnoããlta Bleeker s. 6ãæt¡ H. M. Smith E. E,Jãmorãì- (sIytlì) (eleeker) Cob'' topl i s q"grfl I *'' s-(Vai I lant) 26 Family Siluridae Wallagonia attu (Bloch) hral lago dinema Bìeeker Si lurodes hypophthalmus (Bleeker) õtpõf-E-ñ*." 1" * t lEj ."rr ) Kryptopterus cryptopterus (gleeker) K. apogon (Bleeker r. ETõËr ¡ G'únther Fami ly Heteropneust idae Heteropneustes fossi I is (eloch) Fami ly Clari idae Clarias meladerma Bleeker --6ãtraffi;-Im-neaus) õ. mãffipl-alus Günther Fami ly Schi ìbeidae Platytrop¡us siamensis (Sauvage) Pangas'l_us ìarnaud i i Bocourt P. sutchi Fov¿ler F. Gil-tw-ong se i tl . M. Sm i th P. micronemus Bleeker Þ-. ffierlsl s S tei ndaehner F. Pteropangas ius cu I tratus (H. ¡1. Smi th) F{i qop6ã¡u s Têanãers il-g I eeker fti?ì@nemJ-(al ee[ãr) --:- Family Amblycipitidae Amblyceps mangoi s (Hami I ton) Fami ly Bagridae Bagroides macropterus Bl eeker Leiocassis siamensis Regan FystusMystus ;iTtatusvi tta (Eiãõch) M. nemurus lÑ. and Va.) [.@(Bleeker) M. cavas i u1 (Hami I ton) !"t"rgb"gr"r_ bocourt i Bl eeker Fami ly Sisoridae Baga.rius bagarius (Hami I ton) @r (Boulenger) 27 Fami ly TachYsuridae Hemi p imel odus borneens Î s (Bleeker) Aplochei lus Panchax (Ham¡ I ton) Family Belonidae canci la (Hami I ton) Xenentodon -Is ffiãi]ã¡õ"s I eeker) r"r¡ l, ,*-n *"" Dermoqenys Pus i I I us van Hassel t Family SynaPturidae Svnaptura Panoides Bl eeker S. aenea H. M. Sm¡th Ãchilõ-iã'es I eucorhynchos Bleeker Cvnoq lossus x i Pho ¡ deus uuntner ffioqlossus nrFoÏãplã (Bl eeker) Family Syngnathidae (gleeker) Microphis boaja \ DoryichthYs martens¡ ¡ (l'etersJ Family Anabantidae Anabas tes tud i neus (Bl och) HffistomeGffiã¡ i Cuv. and Val ilphõ nemu s go ramy CcePede Ti¡iãopsrl llTÏã-rus (cuv. and val T. pumi lus Arnold getla sp-jendens Regan ffiñ-o@(cünther) T. trichoPterus (Pê llas, !. pectora I ts lKegan/ Fami ly 0phicePhal idae 0ohicephalus striatus Bloch qàchua Hami I ton 0. + õ-. -Tuc¡us Cuv. and Val. õ. mTã-opeltes Cuv. and Val ' Fami ly PolYnemidae Polvnemus Paradîseus Linnaeus i: ..?, 28 Fami ly CentroPomidae Chanda thomasi (oay) c.-woi-fFlT-(B I eeker ) õ. li-ãnenl¡s Fowler d. EãffiÎ-amil ton Fami ly Lobotidae Datnioides microl ePis Bleeker Fami ly Nand idae Pristolepis fa:ciatus (eleeker) Nandus nandus (Hami lton) [.@@(craY) Fami ly Toxotidae Toxotes cha tareus (Hami l.ton) Fami ly Eleotridae 0xyelèotr i s marmoratus (B leeker) Family fciaenidae John i us dussumi er i (Cuv. ) Fami ly Tetraodontidae Tetraodon leiurus Bleeker @ilton choffih¡nus nari tus (Richardson) 'k ldentifications were made by the Aquatic Taxonomy Unit, National Inland Fishery lnstitute' Thai land' 2g Table 6. Fish land ing statistics for Bung Boraped Reservoi r, tg65-1975. Year Fish Landing Statistic Remark (kg) 1965 862,4\5 1966 846,070 1967 Bo7,3Bo I 968 4zz,305 1969 535,\55 t97o 4\3,243 t97l 467,5O2 1972 I ,oB¡ ,665 Draining period 1973 678,598 197\ Ç73,te6 1975 " 723,048 n Fro* the Nakhon Sawan Fishery Station Annual Report, 1975. t: ::: j:. l:...a.-: 30 RESULTS t. l,la te r Monthly values for nutr¡ent elements and major ions in the Grass Area, the Weed Area and the Open llater Area are given in Tables 7, B and g. The figures showing changes of nutrient elements and major ions in the Grass Area (g), the Weed Area (C) and the 0pen l'later Area (D) are given in Figures 7 and B. Temperatures were s imi lar in al I three areas throughout the lear, v¡i¡11 temperatures ranging between 27 - 3loÇ during the year except in April and May when temperatures rose to 33 ' 3\oC. The mean temperatures for the Grass Area, the l^Jeed Area and the Open l¿/ater Area were Zg.7oCr 26.8oC and 28.9oc respectively (ra¡l es 7, B and 9). Transparency in all three areas was quite low because of the high production of phytoplankton, similar to that observed in the Great Lake of Cambodia (Mizuno and Mori, 1970). Transparency readings could not be taken in the Grass Area because it was so shallow (ranging from 0.3 m in April to 1.0 m in 0ctober) that the bottom could always be seen. The average transparencies in the Weed Area and the Open l^/ater Area were 0.77 cm and 1.34 cm respectively. Transparencies were lowest in August (0.5 cm in the h/eed Area and l.l0 cm in the Open lJater Area) when the water level bJas very low due to evaporation, and turbulence stirred up the lake bottom. In September considerable quantities of inorganic material brought in with the inflowing river water kept light penetration low (raut es 7, B and 9). 31 l. Some major ionS ánd nutrients l. I Electrical conductivity Electrical conductivity in the Grass Area ranged from lì2 to 176 nicromhos. Levels remained fairly constant for November 74 to February 75 (between 160 - t65 micromhos) but rose in March and April (between 175 - 176 micromhos). This was probably caused by decomposition of grasses. Electrical conductivity in the V/eed Area ranged from l0B to 170 micromhos, and in the Open Water Area from l14 to 165 micromhos. The relatively low electrical conductivity which occurred in all three areas during the period August to October was probabiy caused by rain water during the high flood. 1.2 Total hardness Total hardness in the Grass Area ranged from 4O to 7O ng/1, in the Weed Area f rom 40 to 68 mg/l and in the Open l'/ater Area from 40 to 70 ng/1. These ranges agree with several investigations on similar impoundments in Thailand (\,laewgam, 1970:' Sisoowanatad, 1970 and , Boonsom 1970). Balon and Coche (lgZ4) indicated a range of 25 - \5 n7/l for reservoir's of the world. 1.3 Alkalinity Total alkalinity in the Grass Area ranged from 55 to B0 mg/1, in the l,leed Area from 40 to 90 mg/l and in the 0pen Water Area from 40 to 90 ng/1. These levels indicate that sufficient base (mainly calcium salts) is present to enable the C03-HC03-CaC0, buffer system to operate effectively and thus prevent great fluctuations in pH. Hooper and Ball (1964) srare thar the high rate of activity of bacteria and algae which can occur in tropical regions may lead to extremely rapid utilization of phosphate ions, bringing more and more of the calcium ion into solution' Bung Boraped shows'ahigh concentration of phosphate. Therefore a hign concentration of calcium În the water could be expected. 2.',) 1.4 Chloride Chloride concentrations ranged from 9.0 to 17.5 ng/ I in the Grass Area, 7 "5 to 20.O ng/ I in the l^leed Area and 7.5 to 15.0 mg/ I in the 0pen Water Area. The highest of these concentrations are relatively high compared with the world freshwater average of B.16 nS/l (Hutchin- son, 1957). Chloride usual ly or¡g¡nates either from the sea or from ground water. Bung Boraped was part of the sea several thousand years ago and the basin retafns relativeTy high amounts of chloride. 1.5 Sul_phate Sulphate concentrêtion ranged from l5 to 26 ng/l in the Grass Area, l0 to JB ng/l in the \./eed Area and 2 to 30 mgll in the Open l'later Area. The concentration of sulphate in all three areas rose during August to September (to Z6 - 38 mgll). This increase was probably due to additional sulphate brought in by flood water from the surrounding a!-ea. Sulphate is chen¡icaì ly stable in aerated lvater and forms salts of low solubility such as calcium sulphate, sodium suìphate and others. The concentrations of sulphate in fresh water usuaìly lie between 3 and 30 r¡g/ I (Hutch inson , 1957'¡ . Because the water h/as alwaYs wel I oxygenated hydrogen sulphide, which is very toxic to aquatic I ife, could not be detected desPite the h igh concentrat ion of su I phate. 1.6 Phosphorus The rangesof ortho phosphate concentrations in all three areas appeared to be similar. The range was f rom O.l to 0,4 ng/ I in aì I - three areas. Phosphorus is an important element for the grovrth of aquatic vegetation and stimulates primary production. Even small amounts of phosphorous (0.01 mg/l ) can promote the growth of phytoplanlcton, algae and other aquatic plants (Keup, l968). Most phosphorus is tied up either in organisms or in solids (Odum, l97l). In lakes l0 percent is the maximum likely to be in a soluble form. During periods of rapid growth of producers, all of the available phosphorus may become tied up in producers and consumers. Pomeroy (lg6O) suggested that measurement of the concentration of dissolved phosphate ¡n natural waters gives a very limited indication of phosphate avail- abi I ity. Hepher (1963) reports that in lsrael 0.5 ngl I of dissolved phosphorus is optimal for good fish production. 1.7 Carbon dioxide The C0, concentration was highest in the Grass Area, in the range lO - 32 n1/l. In the Weed Area surface level concentrations ranged from l0 to 2\.4 ng/l and at the bottom from 12 to 36 ng/\. ln the gpen llater Area the surface concentration ranged from 6 to 22 ng/l and at the bottom level fron 7 to 25 ng/l- High levels of C0, concen- tration ín the Grass Area were caused by decomposition and low water level. The concentration of C0, within the three areas appeared to be quite high. High CCt, levels may have a negative impact on f ish but fortunately each peak of high concentration vyas of short duration, usually occurring on calm and hot days. l.B Hydrogen-ion concentration The pH ranged from 6.2 to 7.9 in the Grass Area, 6.5 to 7.2 in the l./eed Area and 6.6 to 7.6 in the Open l,/ater Area. The lowest pH values were recorded in September (6.2 in the Grass Area, 6.5 in the Weed Area and 6.7 in the Open Water Area), and were probably caused by the inflowing river water. The pH is regulated by acidity and alkal inity in the buffer system. The fluctuations of pH are caused bY decomposition of organic matter, inflow of ions f rom soils, runoff , and photosynthetic act¡vity of aquatic plants. \^Jarren (lgZt) reported that wide d iurnal f luctuations of pH in natural waters can result frorn the photosynthetic activity of algae and other submerged 34 plants, r^/¡th increase during the dayl ight hours and decrease at night. Moore (1g68) states that in the most productive freshwater lakes the pH is in the range 6.5 ' 8.5. 1.9 oxygen The oxygen concentration in the Grass Area ranged from 2.0 n1/l in September to 9.0 mg/l in November. ln the Weed Area the.isurface level concentration ranged from 2.0 to 9.0 mg/ì, and at the bottom from 1.0 tc T.O n}/l. ln the open V,ater Area the,surface level concentration ranged from 3.0 to !.0 mgll. The dynamics of the concentration of dissolved oxygen depends on the uptake of oxygen from the atmosphere and oxygen production by the photosynthesis of aquatic plants on the one hand, and by respirat¡on of organisms and decomposition on the other (Umnov, l97l). The low oxygen concentrat¡ons rvhich occurred in al I three areas in September were probably caused by the inflowing flcod water from the surrounding lake area. Figure /. The major ions in vrater samples from the Grass Area (B)' the Vleed Area (c) and the Open I'later Area (0) . SULPHATE CHLORIDED ALKALINITY HARDNESS CONDUCTIVITY \ ppm, ( ppm) ( ppm) ( ppm) ( ¡mho/cm) l\) å lu o I i.¡ õ o(¡ d, o) cn oo o iCo O o o 2 o r?r 0 t!i m ¿t c) lti e.q l: I I q it Þ ¡9P tii dó òb z 6ã6 :t Vt mï dd (tt Yi Þ= Ð .ItÞ =Þ e zc ec t- Þc 6, i. :, : 'I :-1,li. 't,r' . : .,,i .; ,j. ,,:,,i i Figure 8. The nutrients elements in water samples from the Grass Area(g),thel.leedArea(c)andthe0pent^laterArea(0). OXYGEN OXYGEN PH CARBON DIOXIDE CARBON DIOXIDE PHOSPHATE BOTTOM (ppm) SURFACE (ppm) z oÞç o o : t! : ll I : ll m cÞE Þþ c) '.F.. .. 1 e 1 Þ 1l z @F ./: -rl t. m /i ot t:le t.' r. P..I: c 7Þ {r Þ t. -t ebã Ð ill : 3 e R Cc : z ô.. e( ac ¡- b.. .Þ c o 6) Þetrl:t fr.I, l: I t*rì l:t o l:t c) 'o -R. ^.-^oC)tD -4 z o I o m c) (¡) ? ":!: fÈ_:::: ;. 37 TABLE 7. The nutrient elements and major ions in water samples from the Grass Aiea (g). NOV DEC JAN FEB APR SEPT OCT NOV DEC Depth(m) I .0 0.8 0 ,7 0.5 0.4 0.3 2.5 2.7 r.3 r.r l,later temp("C) 3¡.0 27.0 28.0 27.0 30.o 34.0 30.o 30.0 30.0 30.0 Transp (r) o. B 0.8 0.7 0.5 0.4 0.3 0.6 1.0 0.6 0.8 Phosphate (pp*) 0.2 0.3 0.4 0.4 0.4 0.3 0.3 0.3 0.3 Carbon dioxide (ppt) r6.0 23.0 23.0 28.0 28.0 32.0 r B. o I 0.0 l2 .0 I 0.0 pH 7.1 7.6 7.6 7.0 6.9 6.9 6.2 6.6 7.2 6.9 0xygen (ppr) 6.0 6.0 6.0 4.0 3.0 3.0 2.0 6. 0 9.0 8.0 Conductivity (umho/cm) i65.0 r60.0 160.0 165.0 176.0 175.0 120.0 I 12.0 1500 1340 Hardness (pp*) 65.0 65.O 60.0 4O.O 50.0 50.0 45.0 60.0 70.0 65.0 Alkalinity (ppt) 60. 0 60.0 60.0 "60.0 65.0 60.0 55.0 70.0 80.0 80.0 Chlorided (pp*) - 13.0 r5.0 12.5 ll.5 10.0 9.013.017.5 Sul phate (pp*) - t5.0 lB.0 15.5 15.5 2\.0 26.0 18.5 lB.0 (C). TABLE 8. The nutrlent elements and maJor lons ln water samples from the lJeed Area N0v DEC N0v DEC JAN FEB APR MAY JUN JUL AUG SEPT 0cT Dept (m) 2.1 2.0 t.8 r.5 t.4 l.z l.t 1.0 1.0 1.2 4.0 8.4 2.\ 2.2 l,/ater temperature ("C) 3z.o 28.0 28.0 27.0 29.0 33.0 34. O 30. O 30. O 28. O 90.0 30.0 30.0 30.0 Transparency (m) 0.6 0.6 | .0 0.7 0.8 t.0 0.8 0.9 0.6 0.5 0.5 1,3 r.0 0.5 0.3 Phosphate (ppm) ' 0.2 0.1 0. 1 0. | 0.2 0,2 0.1 0.2 0,2 0.4 0.4 0.2 Carbon díoxlde - Surface (ppm) 20.0 2\-\ 17.0 24.0 20.0 2\.0 24,0 t6.0 20.0 10.0 ¡6.0 12.0 12.0 10.0 Carbon dioxide - Bottom (ppm) 18.0 32.2 2\.0 28.0 20. 0 2i{'. 0 36.0 r 6. o 22.0 24.0 ¡8.0 15.0 14.0 12.0 pH 6.8 7.0 7.0 7.0 7.1 7.2 6.9 6.9 6.8 6.9 6.5 6.6 6.8 6.6 q.o 6.0 4.0 5.0 2.0 6.0 9.0 7.0 0xygen - Surface (ppm) 4,0 6.0 5.0 3.0 3. 0 3.0 ir 6.0 Oxygen - Bottcm (ppt) 2.0 3.0 2,0 3.0 3.0 I .0 r.0 1.0 2.0 2.0 2.0, 6.0 7.0 r q6.0 129.0 Conduct lvi ty (umho/cm) 160.0 r50.0 I 68.0 r 70.0 165.0 " l60.o | 65.0 | 46.0 140.0 r 19.0 t20.0 108.0 Hardness (ppm) 55.0 \2.0 40.g 45.0 50.0 40.0 55.0 60. o 60. o 40. 0 40.0 60.0 68.0 6¡. o Alkal inl ty (ppm) 65.0 52.0 4o.o 50.o 65.0 60.0 75'.0 82.0 80 . 0 72.5 65.0 70.0 90. 0 85. 0 Chlorlded (ppm) - 14.0 20.0 12.5 l5.o r0.0 l5.0 r8. o 17.5 7.5 7.5 ¡ 0.0 ¡ 3.0 Sul phate (ppt) - 12.0 10.0 r 5.0 ¡ 6.5 lt.0 ¡1.0 | 5.0 36.0 38.0 20.0 t 6.0 t8.0 TABLE 9. The nutrient elements and maJor lons In water samples frorn the open l,tater Area (D) NOV DEC JAN FEB MAR APR I4AY JUN JUL AUG SEPT OCT N0v DEC Dept (m) 3,2 2.9 2,5 2.3 2.2 2.0 1.7 1.7 |l'6 t.2 4.3 5. I 4.0 3.2 !/ater temperature ('C) 31.0 27.O 29.0 28.0 28.0 33,5 34.0 3r.0 29.0 28.0 30.0 3l .0 29.0 29,O Transparency (m) 1.3 r.4 r.4 1,7 1,2 t.8 t.5 r.3 r.3 t.t l.l 1.3 1.2 1.2 Phosphate (pprn) 0.3 0.2 0.3 0.4 0.4 0.2 0.2,, 0.2 0.2 0.3 0.4 0.2 0.3 Carbon dioxide - Surface (ppm) 12.0 22,0 t2.O t l.O l¡r.0 16.0 20.0 12.0 ¡2.0 6.0 16.2 10.0 ¡6.0 10.0 Carbon dioxide - Bottom (ppnr) ¡ 6.0 25.0 r 4.0 8.0 18.0 2\.0 20.0 t 6.0 ¡ 4.0 8.0 ¡4.0 t8.0 7 .0 18.0 pH 7.4 7.2 7.6 7.\ 7.4 7.0 7.\ 7.0 7.2 7.3 6,7 6.6 7.0 6.9 Oxygen - Surface (ppm) 6.0 5.7 8.0 8.0 8.0 6.0 8.0 7.0 9.0 8.0 3.0 8.0 8.0 7.0 Oxygen - Bottom (ppm) 6.0 4.0 7 .o 5.0 7 .0 6.0 6.0 6.0 g.o 7.0 3.0 8.0 7.0 7.0 Óonductlvi ty (umho/cm) 160.0 t40.0 ¡40.0 t68.0 r55.0 t65.0 t60.0 ¡40:0 ¡43.0 il4.0 1 15.0 | 08.0 I 47.0 | 30.0 ltardness (ppm) 50.0 45.0 qo.o 40.0 50.0 50:t0 65. 0 60,.)0 60.0 55.0 40. o 50.0 70.0 65.0 Alkalinity (ppm) 50 .0 53.o 40.0 75.0 65.0 65.0 75.0 83.0 75.0 70.o 60. 0 60. 0 90.0 85.0 Chlorided (ppm) - t0.0 12.0 12.5 12.5 !5.0 ¡5.0 ¡5.0 r5.0 7.5 7.5 12.5 ¡ 5.0 Sul phate (ppm) - 2,0 6.0 r 5.0 9.5 12.0 8.0 r0.5 30.0 29.0 27.0 ¡5.0 t6.0 u) \o :'r 40 2. Sed iment Dataonsedimentparticlesizedistribution,phosphoruscontent and organic matter are given in Tables 19 - 27 and Figure !' Particle size distributions are presented as percentages t in (Dewis three major categories according to the International System ancl Freitas, l97O). Phosphorus is presented as ppm of P and organic matter of as percentage loss on ignition. ln general the bottom sediments Bung Boroped are composed of fine textured mud and clay-type soils, occasionally with a small amount of fine sand. The soÌlsare normally blackordullgrayincolourandappeartobepoorlydrained. According to the soil analysis performed in two periods (November |g7\.AprillgT5andSeptember-December1975)theorganicmatterin the Grass Area ranged f rom 5.65 to 10.38% with an average of B'\4%' average The phosphorus content ranged from B.58 to 16.58 mgll with an of ì1.99 ng/1. The average sediment distribution in the Grass Area was ln the l'leed Area S.o\y. of f ine sand,3l .51%"of silt and 61 .687. of clay. the organic matter ranged f rom 2.60 to 5.8\Z with an average of 4'06%' average The phosphorus content ranged from 4.91 to 9.83 mgll with an of 7.68 ns/1. The distribution of sediment was 12.54'Á in f ine sand, lJater Area the organic 30.51% in silt and 56.78% in clay. For the open matter content lay between 2.75 to 6.54% with an average of \'30%' The phosphorus concentration lay between 9.00 to 12.08 mg/l with an average of of 10.06 ng/\. The particle size was distributed in the proportions \.517" of f ine sand , 42.11% of s il t and 53'\9"Á of cìay' 2.1 'Comparison of órganic matter The average organic matter content was highest (8.44%) in the Grass Area and was signif icantly different (p( 0.01) from the V/eed Area and Open Water Area (l+.06% and 4.30%, respectively). There was no signif icant change over time (fanle l0). The organ¡c matter is probably highest in the Grass Area because of decomposition of grasses, and also heavy sedimentation within the I ittoral zone related to the water-level manipulations. The organic detritus, humus and other organic matter undergoing decomposition are important to soil fertility. Table lO. Analysis of variance for organic matter among the Grass Area (g), the l,/eed Area (c) and the Open l^later Area (0), excluding 'the dry months May - August 1975- Sou rce DF Sum ofl Squares Mean Square F-Value Area 2 | \57 .016 72B.5oB 66.297 I lme 9 173.847 19.316 | .757 Area I tme 8 2 r 8.808 12.156 t.106 Res idua I r50 1648.27 5 | 0.988 :j:.::...... ,.....:.:;.".t::,;...... '.i..''...i.:ì:..::...::,.)--...... -.J.r 42 2.2 Comparison of phosphorus The phosphorus content in the sediment was highest (11.99 mg/l) in the Grass Area. The Open Water Area was second (10:06-mg/l) and the l^Jeed Area lowes t at 7.68 ng/ Areas B and D were There was significantly different (p (0'Ol) from area C' ' also (Tables ll and l2) a signif icant difference (p(0'01) among times' The phosphorus concentration from all three areas appeared to be high during November to February and then decreased very sharpìy in the sumner months. It is likely that the phytoplankton bloom in the warm season was taking up phosphorus from the water, and indirectly from the soil. From September 1975 the phosphorus in all three areas dropped to the lowest poinr, 8.58 mgll in B, 4.91 ng/ I in C and 7.16 ng/ I in D. These values indicate that the inflowing water from outs¡de the reservoir must affect the phosphorus content of the sediment Phosphorus is a major nutrient required for primary production in the aquatic ecosystem (Kuhl, 1962). H¡ckling (1962) stated that of all the nutrients phosphate appears to be the most important for fish culture. -HE. u¡vflÈry i-Su*H' :,:.*it '..':. :-i ... ..:- . .-: .'-: :, . ::. :: :-- :. .+Jl, .) Table I l. Analysis of variance for Phosphorus among the Grass Area (g) , the ì,leed Area (C) and the Opeir l,/ater Area (O) , excluding the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Value Area 2 ttzt .173 560.586 2t .g28""' I lme 9 768.t6l 85.40 I 3.340"" A rea t8 531 .945 29.552 r.r56 Res i dua I 383\.602 Table 12. Analysis of variance for Phosphorus between the tr^leed Area (C) and the Open \,later Area (D) overthe period of 14 months, including the dry months May - August 1975. Sou r ce DF Sum of Sqr-rares Mean Square F-Value Area I 549.785 5\9.785 46.952 I tme t3 1639.315 4l.lgg 4 .081 Area l8 621 .321 |6.20r r.oB3 Res idual 2t0.615 44 2.3 Comparison óf the particlè size distribution 2.3.1 Fine Ser4-traction (O.Z - 0'02 mm) The f ine sand f raction in the l,leed Area (12.54%) was found to be higher ( n ( o.or) than in the Grass Area and the open \^/ater icant Area (S.Oll and 4 .51% res'pectively) ' There r^/as no signif differenceamongtimes.Aninteractionbetweenareaandtime was found only in the analysis of variance for all three areas' leaving out the dry period. There was no significant inter- action in the analysis of variance for the vJeed Area and the open l^later Area wi th al I times incl uded, wh ich suggests that the interaction may be caused by the sharp decline in percent sand for the Grass Area in November (Tables 13 and l4). This could indicate that the drop in h/ater level caused by evaporation after November 1974 may have affected the I i ttoral zone more than the other areas. 45 Table 13. Analysis of variance for Fine sand fraction (0.2 - 0.02 mm) among Grass Area (g), the Weed Area (C) and the 0pen l^/ater Area (0), excluding the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Va I ue : : Area 2 \842.505 2421 .252 13g.566'k'k I lme 9 885. 870 gB.43o 5.633 Area x Time IB 896.990 49.832 2.851"" Res i dua I 150 2621 .033 17 . t+73 Table 14. Analysis of variance for Fine sand fraction (O.Z - 0.02 mm) between the Weed Area (C) and the Open l^Jater Area (0) over the period of l4 months, including the dry months may - August 1975. Sou rce DF Sum of Squa res Mean Square F-Value Area 6609.2t\ 6609.214 T ime 52t+.236 40.325 Area x T ime 664.114 5l . toz :.:' Res idual 6063.986 43.314 ';,:;':.::1-::raa:,1-:a.: :,1 i:t t :'lr: : : ; 46 2.3.2 Silt Fraction (0.02 - 0'002 mm) ( O' 0l) in the The f raction of silt was signif icantly higher-(p openWaterAreathanintheGrassAreaorthe\r/eedArea (\2.11% in D, 3l .51'Á in B and 30 '51% in c)' There was a significant (p ( o. 0l ) interaction between area and time' The of difference between area B areas C and D in the pattern fluctuationofpercentagesiltapPearedtobethemaincauseof interaction.ThefractionofsiltinbothCandDwasobserved todeclinegraduallyafterNovember:tg75,whileitincreasedin BfromNovembertoDecember,andthenwasslightlyvarîableunti April (ra¡le l5). (O.OZ - 0.002 mm) among Table 15. Analysis of variance for Silt fraction the G¡-ass Area (B), the l/eed Area (C) ap' the 'Openli - Augus t' 1975' Water Area (O), excluding the dry months'l'lay Mean Square F-Value Sou rce DF Sum of Squares \957 .780 tz['.g\,7"t'- Area 2 99t5.561 68.7\3 1.787 I lme 9 6tB.68B -l- -L 2.476"" Area IB 1713.563 95.197 Res i dua I 5767 .205 38.348 :. !1.:,1:a;l :,:.:,:.ì.:.:.::.:. 47 Theanaìysisofvariancebetweenthet,leedAreaandtheopen (data from May - August lJater Area, over the period of l4 months areas and among were included), showed that differences between fraction times were significant 1O( O.Of) (Table l6). The Percent Area was observed of si lt in both the Weed Area ancl the Open \,/ater respectively), to be highest in November 1975 ß\.\o% and 49 .29% fluctuated over then dropped gradually until March and finally time until December. (0 .02 - 0 .002 mm) Table 16. AnalYsis of variance for Silt fraction Area (D) over the between the Weed Area (c) and the 0Pen lJater August 1975' period of l4 months, i ncl ud i ng the drY months May - F-Va I ue Sum of Squares Mean Square 1565.546 Z6t+.660"" Area I t565.546 tL.L t\o.967 3.225 I tme t3 t 83*2 . 5Bo 38. I 3o 0.583 Area t3 \9s.loo Res i dua I 6tt7 .939 2.3.\ Clay Fraction (less than 0'002 mm) ThepercentdistributionofclaywashighestintheGrassArea and intermed iate (71 .86%), lowest in the open llater Area t53.\9Ð, areas B' C and D' in the t'leed Area (56'7[lÁ) ' The differences among (p ( There were also and between c and D, were significant 0.01). significantdifferences(p(0.01)amongtîmes(raulelTandlB). TheintensityofdecompositionofgrasseswithintheGrassArea The wind-protected could contribute to the high percentage of clay. 48 ''''.'':r' character of the Grass habitat would help the accumulation of clay by protecting the area from wave action. The fraction of clay from all three areas appeared to increased slightly after November 1974 as the water level started to recede and the temperature increased. This suggests that the decomposition of aquatic plants may be the .,,1'-"' major source of sedimentation and the build-up of clay in the reservoir. The clay particles may be the majoT cause of the changes in percent composition of silt and fine sand. That is, a change in ,,-,,,t,,,,,,., ...... - .:...... : . amount of clay will always alter the percentage of both silt and t. -::-::--j.:, -:.:.:: f ine sand even though they themselves do not change. ':'':::.;'''':" 49 Table 17. The analysis of variance for Clay fraction (less than 0.002 mm) 'a1j Area (B), the bfeed Area (c) Onen ämong the Grass _the Water Area (o), excluding the dry months May - August 1975' Sum of Squares Mean Square F-Val ue \072.t+28 2037 .7 | 4 zB.o47'v' -L -r- 2154.050 239.338 3.294"" 584.485 32.741 o.\46 Res i dua I 10897.930 Table 18. The analysis of variance for clay fraction (less than 0.002 mm) between the Weed Area (C) and the Open Water Area (o) over the period of l4 months, including the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Value A rea I 763.820 763.820 20.962 .L.L I tme l3 201\.O55 154.927 \.257 Area x Time t3 n2.2\B 25.565 0.70t Res i dua I r40 5l0l .358 36.tl38 and Part i cle Size Distribution of Figure 9. 0rgani c matter, PhosPhorus (g), weed Area (C) and the soil sedirnent in the Grass Area the Open Water Area (o) ' :ìi:r,l;::;:iiiii;r:::r:iÍ:¡:ii::;iì:liìl: j 50 t2.6 É ÑO WATER IN (B) DURING SUMMER MONTHS td t-- E:--E---o-- k B___l // o o\ \ 7.6 \ 9:a \b' (9ãù oE, 2.6 2r.o U)f, o?É. 1E Ào r3.o 9., a -t- fL B_ d E E ro.o o$J o zl oc.l tro o.o f s0.o =-oL:2 gt)l-- E õE (\J lrJ O 37.5 6oNO I o...... *'+ t40N .o...... "--írt-.-S- do t- 25.0 É 70.o tr- ña /\* R--o---€---o -s / ¡F--È-\E ; E 57.5 o(\I o c, V 45.O DEC JAN FEB MAR APR MAY JUN .JUL AUG SEP OCT NOV OEC E--{B) o...... (cl +(D) TABLE I9.' The mean and 958 confldencå llnrlts of 0rgantc Hatter, Phcsphorus and Partlcle Slze Dlstrlbutlon In soll samples from the Grass Area (B). T IME NOV DEC JAN FEB ¡IAR APR SEPT 0cT NOV UEL HEAN | 0. 8.975 8.4¡'6 Organic matter 9.058 7,375 383 9.ll7 9,283 9.400 5.658 7.283 7.925 (r) (s. ¡¡o- (\.822- (4. rB5- (6.961- (s. otg- (6. 989- (6.66\- (2.9 r 0- (2.803- (5.836- | 2. 630) 9.928) I 6.58t ) ú.27tÌ I 3.550) | 0.957) | 2. t56) 8. q06) 1t.763) ro.orB) Phosphorus (pprn) n.575 I tt.250 t4.4t7 | 6. !83 | ¡ .250 | 0.583 9.250 I .583 I | .500 t 2.000 n .ggg (8.zgo- 15 .577 - (\.zee- (9 .88o- (6.539- (8.7?5- ß.sso- (4.03 t - (9.25t- (8. ¡sz - t5.rt5) 22.923) 2\.5331 23.2851 r5.96r) t2.q4t) I 4. 549) 13. t35) r3.749) I 5.6q8) Flne sond (?) 14.217 5.5\2 2.6\2 2.6t9 3. ol7 4.683 3.517 4.o08 5. 000 5.2\2 5.0q8 0.2-0.02 rm (l l.l{26- ( ¡ .833- (l.zgo- (l.8qo- (0.75 | - ß.622- (r.560- ( | .799- (4.5r3- (3.836- l7.006) 9.2\91 ' 3.670) 3.382) 5.28 t ) 5.7\\) 5. \72) 6.217) 5. !87) 6.6tr7) st tt (u ) 27.508 33.\t7 27.\33 ß.218 32.'Ð50 3¡.700 3 | .950 33.800 32.019 3t ,\25 3t .512 0.02-0.002 mm (24.5oq- (29.385- (z9.ogz- ß0.707- (28.606- (29.82q- (28.303- (¡t. tso- (zg.tl l- (29.012- 30.5t4) 37.\\71 33,348) 35.7261 36.679) 33.5761 35. 099) 36.450) 3\.7?tl 33 .856) clav (t) 58.275 61 .04 ¡ 56.358 64. | 67 6\.333 62.81:7 6\,533 62.t92 62.983 60. t66 6¡.687 <0. 002 $2.959- 157.325- (6t.ozl- (6¡. | 62- (59. z ¡ o- (38.31t5- ß1.338- $l.ttz6- (60.607- $7.262- 63.59t) 6\.7571 69,3931 67. I 70) 69.45r) .67.287) t9.723) 58.6¡6) 65.36q) 63.030) L,I H ',t .: 'i. 'l / i IABLÊ The.tn?ôn ¡nd confldenco Qrganlc portlclc LV2¡ 951 tlmtts of ¡tsttcr, Phoiphorul and St¡e Dlstrlbutlon ln soll sample frcrn the r¿lecd Area (C). ,ll ,1.;. :iil i ':: T¡ HE ;,ì)l i:, .l:, t:i.l iì:: r'iì ,i¡l Ìii ,1, l"' :":' '',: .1,,1 r;i: ';i:;: þ" (tl hJ slze TABLE 2L The r¡eðn and 951 confldcncè llmlts of 0rgantc Hqtter, PhosPhorus.and Pertlcle Dlstrlbutlon ln soll samplc fron the opcn l'later Arca (D). I fI ME HEÀN APR . },fAY N0v DEc (10 u.) (14 ¡0.) IEB. . 0rganlc matter 6.5\2 \.375 3.69? \.\\7 3.967 \.2t7 I|.700 4 .708 4. 3oo 4,358 4. | 42 2.750 5.000 3.ssz q. l0q 4.¡6q (0. il0- (q.oBo- (3.495- (q. oz8- (0.439- (3.533- (3'589- (4.048- (2.37\- (t .362- (4 . I 97- (3.t56- q.670) ß;352-'(4.0r'0- I 2.954) q.o3o) 4.892) 4.837) r,.404) 5.627) 5.878) 5.0l I ) \.7t2) 5.408) 3.938) 5.803) \,626') Phosphorus 9.004 II.oB3 8.583 12,917 9.583 t.!.083 9.000 11.666 l0'833 | 2.833 7,167 9.0\2 I t.033 10.066 tz.3t6 (ppr) (8.669- (t0.47r, (7.812- (l t.373- (8.r'63- (l r .800- (z.gor- (lo.3q5- . (9.958- (il.06r- (\,782- 17.Sjs- (z.622- rall;11? 9.331) 11.695) 9.353) r4.459) ro,703) r2.591) r0.099) ¡2.978) il.808) l 4.605) 7.550) t0.52?, 1.2 ,\37, 12,97\" l|.rrql q.z Ftne sand (?) t.i¡g 2.833 4.083 5.300 5.775 3.842 r6 3.673 1.525 6.0t7 4.3 1 7 4.283 q'51I' rr'l5t 0,2-C.02'nm (2.856- (2.22\- (f .¡'88- (J.7\6- (2.953-. (3.ooz- 12.gzt- (z ,7go- (3. I 9lr- (2,606- (3.7t9- (3.050- (3.783- rt.l¿i3o 6.855) ß,597) 4.630) 6.¡61) 4.070) 4.44t') 8.313) 5.283) 4.739) 5.859) 3.\\2, 6.376) 5.6\21 5.582) !Jl qo. ':l' silr (t) \9,292 ¡t5.508 43.012 lrl.383 38.q00 \2,683 34. r9l toB, 43.891 4r.84t 36,367 ql.l92 t2.OoO \1.7e7 (28.969¿ 42.lll 0.02-0.002 |ffrì (Bz.857 - (4 3.740- ß8,7\3- (36.912- (33.61t'- (\0,137- l3z.52o- ß6.9t7- l\t .972- (40.278- (37.363- 136.286- al'.;?32 ' t qq.rr20) 51.723) ¡t7. I i6) \2.33\, ¡t5.354) l'3.ì3q) \j.g7z) \3,27Ð 45.010) {3. {ot ) h3.7t3) 44.4 | 7) \7.705:- 42 .880) I clay (t) 46 .3So 5t .775 52,875 53,J17 55.825 53,392 57.366 o).o/) >¿.cl> 5\,6'11 57 ,617 5\,\73 54.550 4eB' (50'684- (53.80q; 53' 53'e37 <0..002 nun (4\,652- (50.37t. (5r.1¡rg- 152,5t5- ß2.239- (ro.726- (5t.696- $2,226- (52.198- (51.t53- ç110.;?,7?. l50,zls- t{ol 18.oqg) 53.379't 54.3il) 56.39t) 58.635) 54.543 ) 64.006) 69.654) 54.2\0) 55. ) 63 . 006) 56.780) 57.650) 56.8 I 2) ur \9 '''': 54 3. $luat i c Mac roPhytes ìimits of aquatic macrophytes Data on the mean number and 95% confidence foundintheGrassAreaandl^leedAreaarepresentedinTables22-23 andFigurel0.Theanalysisofvarìanceontheabundanceofeachplant speciesfromtheGrassAreaandthe!,/eedAreaarepresentedinTables col lected in Bung 24 ' .30. Forty species of aquatic macrophytes 'were Boraped during this study (faUle 2)' Leersiahexandra,Hymenachnepseudoiterug,Cynodondactylon (allGraminae),lPomiaaquatica(convalvulaceae)andPoìygonum tomentsum(Polygonaceae)arethemostabundantspeciesinthe cucul lata and Nelumbo I ittoral zone. Eichornia S.¡9-ssj-Pes-, þþ!.11þ nuciferaarethemostcornmonfloat¡ngspecies.Cyperuscephalotesand IsachnegìoÞasa,whichcouldformthesuddcommunitywithotner plants, contribute to the formation of floating islands (Tongmee' 1972 and lg73i Junk, 1g7Ð : .: .1-, ,:.:1:: :. Figure ¡0. The distributions of major aquatic macrophytes in the Grass Area (g) and the Vleed Area (c). . 55 o-L.hexondm r-...4.cynodon 0 ¿-.-H. pseudoiterum UJÉ U' (f, (9É40 I I zI 9zo f c É l- Ø õo -*') dried up during summer months- t-2 -wol€r ()IlJ É a ------E. crossipes l¡J fL e...... S. cuculloto I I t a-.-C.cepholotes tr-"- l. globoso 960 o-F. milioceoe trl É o40 l¡J IJ 3 .P APR MAY iJUN .JUL SEP ocT the TABLE ,22. The mean and 95"Á conf idence I TmÎts of percent rcover of aquatic macrophytes in Grass Area (e). NOV DEC JAN FEB MAR APR MEAN Leersia hexandra 92.627 9r.il5 94.128 86. 036 36.318 26.401 74.720 fig.667- $t .260- (r2.08r- ß.296- Q3.319' Qs.tsa' gz8) 99,992) 97 . .t 97) 9t+,952) 99.721) 68. 56.045 ) Hymenachne pseudoi terum 3.01 5 \.375 6.363 I.t34 (o-lz.7oo) (o-21.689) (o-zg.2r I ) Cynodon dactylon 35.516 44 .t t2 5.065 (8 .067- ( r 9 .036- 69.713) 70.807) Cyperus di fformi s 3,340 7.949 0.562 (o-zr .498) (o.o¡7- 24.002) Jussiaea repen 0.t+39 0.564 0 .055 (o-s. 446) (o-0.792) Coix aquatica 1.650 0..¡41 0.077 (o-t .6t7) (o-r.r:t, Nymphaea lotus 0. l4l 0.564 0.035 (o-r.zs8) (o-3.772) lpomia aquatica r .43 r; 0.564 0.r41 0.287 0.227 (o-9¡8¡ ) (o-l.tgz) (o-t.758) (o-¡. s66) 0.844 Polyqonum tomentosum 0. B3o 5.141 5.291 l.Jl (o-s.t4zJ (0-67.944) (0.036- o\ I 8.529) TABLE ?3 The nean and 95t confldence llmlts of aquatlc mscrophytos fn the l{eed Area (C). FER NOV APR NOV-APR HAY AUG I.,IEAN I,IEAN llqgllchng pseudoitei.um 2,047 0.055 (o-r3't'93¡ 0.01 7 .- Ffnbrystylls nlllaceae 2.812 o .9q7 .2.370 2,567 1.43t 2.093 7,697 0.596 2.4t\ (o-18.874) (0-tS.h'z, (0-il.374) (0-49.599) 1s-9.48t) (0. r or -25.556) (o-7 .373) lsachne erobgsâ o.tql 17.8t | 2.730 2t.067 | 0.545 15.951 18.85¡l 32.572 8.960 rrl!;i?îrl rc-i:?lZt rc-'r'jïlt (o-r.758) (0.347- (0-67.5761 (0-60.677' .(0-56.838) (o-74.46r) (3.730- 52.559) 72.300) Cyperus cephalores 2,370 t2.04t r | .656 8.759 10.383 il.3t7 7.851 0.493 8.699 l\.220 3.646 9.005 5,376 (o-5 (0-t5.452) (0-5.42t) (t.385- (0-60.460) (o-r7.378) (o-38.s621 (0.2 r o- | . 060) 1o-'lr.oo9) (0-46.562) (o.oì6- | 6. 626) 3ì.663) 38.75\l cvperus r .431 0.152 drrrormrs 0.287 0.596 o.z7o (0- tr'Î:13!l ,r-!:9i1, (o-8.23f ) rc-7.j73) | 7. 076) Elchornlâ 26.99\ ?ô E?ô 25.248 22.209 28 crasslpes .4t.645 46,035 40,SS2 23.20s 25,9\2 15.85ì 3r.607 ¡3.309 ' 306 fl9-.0¡t: Qg,ss - ( 4.5t0- (0-75,7\3, (o-79,4251 (o-59.502) (3. | 35- (3. | 35- (o.tr6l- (2.46:.. (2,763- 77¡868) 6z.7ts) 84.490) 62.7131 7o.o7tl 39.r\2) 6r.943) 52,552') Jusslaea rcpcn - o. l4l o.287 - 0.022 0.041 0.0t tl (0-3 to-i.z¡a¡ ,560) (0- | . 753) Nelumbo nuclfera 1.7\7 O.l4l - 0.297 l.¡q6 0.302 2,867 | ,075 2'972 I .681r 3.427 I .364 (o-¡ | .565) (o-r.763) (o-7.690) to_i.iiål (o- t 3. 45t ) (o-8. 067) (0-28.396) ([.304- (o-r5.236) lpomla 14.243) aquatlca 0. t4r - o.oo4 o.o0¡ ; 1o- r . zsl) 8.669 8.669 8.212 7.929 5.()te r4.608 Salvln¡a cucullata 2q.4\ 7.60¡ 3t;t56 32.932 38, 30lr t2,r38 23.\06 (o- | 4 .665) (o-43.974) (o-40. I (0.270- (o-r to .19ð: (0..i43- (r .osz- (s.¡oe- 25) 3.n4r) ß.s66-'- _. (o-50.360) 28.94t ) i7.275) \5.7691 77'.7\tl il.r¡zl t¿ .ó I5l \¡llJI ',iì' r: 5B 3.1 The der¡elopment of vegetatîon in the Grass Area (B) There were nine species of aquatic and semi-aquatic hydrophytes in the Grass Area (faþle 2\). Among these the percentage cover for Leersia hexandra, Cynodon dactyìon and Hymenachne pseudoiterum rePresented 74.72%, 5.06% and l.l3Z respectively. L. hexandra was the pioneer form in succession, and was slowìy replaced by H. pseudo il!çIr{L as the wa ter I eve I receded i n Feb ruary . g_. dacty I on occurred after the Grass Area started drying. trith rising water levels in September, the population of L. hexandra that survived the May - August dry perÎod increased greatly, and the plants grew up verticalìy and kept their roots attached to the ground. The main flowering time lasts from November to March. After the main flowering time the growth of L. hexandra decreased tremendously, and the plants turned partly yellowish-green. Ufith falling water level the stems clung together more densely and some died, indicating that L. hexandra is sensitive : to dry condition5. Junk (1970) reported that L. hexandra in the Solimoes-Amazon start to die after the water level drops more than I to 1.5 m. In February, after the water level dropped to 0.5 m and the water temperature rose to 34oC,, H. pseudoiterum (which is ver:y simi lar to L. hes¡ndra except that it has a bigger stem with large and thicker leaves) started to expand its population and was detected by the rectangular lxl m measuring frame. ln March another species of Graminae, C. dactylon, bras detected. This species of grass grew so guickly that within two months after detection it occupied up to 44.11% of area B. This grass was observed to survive the very warm climate and drought extremely well, and showed some development during ir.tl::r:l co again the summer months. However as the water level started to rise in the ra¡ny season C. dagtYlon died awaY within a few weeks. (c) 3.2 The distribution of the floeljn-g-weeks the \,/eed Area There was distinct vegetation zonation' Near the shore Coix aquatica (Graminae) was rooted in the substrate. The long arenchymatous stems float in the water, and with their nodal clusters of roots were often more than I m long. Beyond this zone was a floating stretch of lsachne globoSa (Graminae), limbrTstyl is a mi I iacea and Cyperus dîfformis (Cyper:aceae). 0n the outside was wide belt of Eichornia crassipes (Pontederiaceae) and salvinia cucul lata (Cerlatophyl laceae) . Salvi nia cucul lata frequently constituted the sudd formation (Michell, 1969) together with Cyperus ---cephalotes and Cyperus platystyl is (Cyperaceae) ' Because of their formation'and high frequency of occurrence' plants !. globosa and E. crassipes wene probably the most important in the floating aquatic ecosystem. The l. globosa stands mainly occurred inshore from a 5 - l5 m v,,ide belt of !' crassiÞes' The density of the vegetation was considerably greater than in the Eichornia stand and the whole mat was tightly woven together horizontally' From the water surface extending down to a depth of approxìmately 20 cm was a dense layer of roots' stems and deád mater¡al. Beneath this was region of roots and loose dead matter' The whole mat extended to a depth of 50 - 60 cm beneath the water' surface and resulted in a deficiency of oxygen whÎch prevented many aquatic organisms from inhabiting this region. Anoxic conditions also occurrecl w¡th¡n the dense layer and parts contained HrS. 60 E. cras,s ipes is a f loating hydrophyte vri th a wel I developed root system. The degree of horizontal entanglement of the stand was relatively weak so that gas exchange between air and water was : possible. There was therefore suff icient ,-.t ; .-. ,..:..i E. crassipes developed very wel I during the rainy season, with the rise in water level (probably caused by the influx from the Chao out Phya River). However large quantities of E. crassipes drifted ,, . 't,,t..i of the reservo i r due to wi nd act ion. ,.::::i::l - The lJeed Area was f ramed by a belt of bamboo in order to stabil ize '"""' it despite wind and current. In November 1974 E. crassipes and S. cucu I I ata covered \l .64'Á and 24 .83% of the area, respect ively. E. crassipes remained more or less unchanged until January 1975 and then gradual ìy dropped to the lowest (13.307.) in July. Af ter the monsoon season began in August, E. crassipes began to grow faster andexpanditspopulationÈonceagain.!..cucullataincreasedin populat¡on from 24.83y" of the area in November 197\ to 38.30% of the gradual minimum of 5.65'Á of the area in March and then dropped ly to a ;,,.,,., :::'1::: area in September 1975. C. cephalotes, which formed the sudd formation ',1. : S. cucullata, had expanded its population from 2.37% of area in with "'," November 1974 to 12.O\% of area in May 1975 and then remained fairly stable (ta¡le 25 and Figure l0). The expansion of C. cephalotes showed negative correlation with S. cucul lata which had been its substrate. .,Ì,:'ì., a ' :.:.:: It was observed that the increase of C. cephalotes caused S' cucullata to lose its buoyancy which resulted in either sinking or breaking-uP of i ts mat. C. cephalotes sr.lrvived because i ts roots were already the plants enable them attached to the lake bottom, and the density of : 6L to stand. The fìoating Graminae !. globosa advanced from the inner : side of the l"Jeed Area near the shore into the lake as soon as the mats of other hydrophytes were thick enough to be used as a substrate' Near the shore they rooted deeply in the ground but in deep water they and S. cucul lata, with a formed thick f loating mats. E-. crassipes ,,;,,.: loose structure and unstable formation, are Pioneer species and later will be displaced as they provide a substrate for other symbiotic and F. mil iacgae. species such as C. cePhalotes, C. difformis E-' : :' crassipes and S. cucullata appeared to be quite susceptible to the population rvhich created heat during summer, resulting in a decrease of ";; an opportunity for the advance of c. cephalotes. !. globosa was the most successful floating vegetation in the area. lt advanced stead¡ ly fromtheinnersidetotheopenb,ater.ltsolderstandsì^,ereSothick that H^S was present underneath and an aquatic fauna could only ¿ develop at the upper surface. Therefore large areas of Bung Boraped must be regarded as already useless for fish production 3.3 Qúant¡tát¡ve analysis of d¡stribution of aquatic macrophytes distribution The data on the means and 95% conf idence I imits for the ,i.,;. of each vegetation species in the Grass Area over the period of six ;,,,:,, monthS,andintheVleedAreaforeleVenmonths,arepresentedin . Tables 24 and 25. During the month of September Bung Boraped was heavi ly f looded and experienced a tropical storm which caused severe ,:;;,;11 :::':: damage to the study sites. The f loating weeds had al I drif ted away and the Grass Area which had just began to re-estabìish itself was completelY flooded Leersia hexandra (Graminae) varied from 26'40% of the area in April to i2.6zz or the area in November 1974, with 74.72% average l.:,.., 62 cover, and occurred mainly in the Grass Area. Variation over time r.,as signif icant (p( 0.01) as was. the area x time interaction' 'Íable 24. Analysis of variance on the distribution of Leersia hexand ra (Graminae) for the Grass Area (B) and the Weed Area (c) Source DF Sum of Squares Mean Square F-Val ue Area tg.620 lg.620 5l 5 . 06B'*" -r-& I lme r.B7B 0.375 9.860"" -r--L Area I.B7B 0.375 0 .860"" I R., idual I O 2.285 0.078 l-tymenachne pseudoiterum (Gram inae) ranged Î n percentage cover f rom 3.05'Á to 6.36'¿ during February to March in the Grass Area. lt was observed only once in the hleed Area, in November (2.04%). There were no significant differences between areas or among times. The average over the entire study period was 1'17"¿ of cover in the Grass Area' In the Grass Area Cynodon dactylon (Graminae) was first detected in March with 35.51'Á of cover, and later in May witn 44.11% of cover' tt was not found in the Weed Area. D¡fferences among areas and among times were signif icant (p (0.01). The area x time interactÌon was also signif icant (p ( O.0l) (ra¡l e 25) - ..- .-:.::,.:,- ::: ::)"i:::-:':::.i:::::t::::i-i ;': l'ì:-ì ì:::i::.'.:: ::.1i:l;: 63 Table -25. Analysis of var I ance on the distribution of Cynodon dactylorr (G ram i nae) for the Grass Area (e) and the l,Ieed Area (C). Sou rce DF Sum of Squares Mean Square F-Val ue Area I 0.93 I 0.931 61.750"" .L.L ¡ tme 5 | .874 0.374 25.853"" Area x Time 5 1.874 0.37\ 24.851'x Res idual 60 0.904 Fimbristylis miliaceae (Cyperaceae) was found only in the h/eed Area. The plant used Salvinia cucul lata and other stands of vegetation as its substrate. There were significant differences among times (p (0.01). The pìanr constituted 2.41% of the totaì area during the first six months, and O.gg7. of the area over the period of ten months (raut e 26) . Table 26. Analysis of variance on the distribution of Fimbistyl is mi I iaceae (Cyperaceae) for the l^Ieed Area (C) f rom November 1974 - September 1975. Sou rce DF Sum of Squares Mean Square F-Value Time l0 0.522 0.052 Res i dua I 55 r .4r r 0.025 64 lSåchne globosa (Graminae) is semi-aquatic and forms the most important mats of floating Graminae in Bung Boraped. lts abundance ranged from 0.14"Á of the total area in March to 32.57% in September. The average vras 2.73"Á of cover during the f irst six months and'8.96% of cover over the period of ten months. !. globósa rvas found only in the lJeed Area. The distribution varied signif icantly over time (p(0.01) (faUle 27). Table 27. Analysis of variance on the distribution of lsachne globasa (Graminae) for the l,leed Area (C) f rom November 1974 - September 1975. Source DF Sum of Squares Mean Square F-Value I tme l0 2.958 0.295 2.177 Res idual 55 7 .\74 0.t35 Cyperus cephalotes (Cyperaceae) is encountered very frequently ¡n floating stands of Salvinia cucul lata as sudd colonies. I t ranged in percentage cover from 0.49% to l\.22%. The population of C. cephálotes within the framed area was observed to grow much faster and increased at a more constant rate than plants growing outside of framed area, which indicates the impact of the wind upon its deveìop- ment. The plant was found only in the l'/eed Area. The change over time was s ignif icant (p ( 0.01) (faUle ZA) . ¡:. -:'"--: ; :.:_::-:: _::: 65 Table28. Analysis of variance on the distríbution of Cyperus cephaìotes (Cyperaceae) for the Ì,Ieed Area (C) from November 1974 - September 1975. Sou rce DF Sum of Squa res Mean Square F-Value 0.¿6 t6 0. 061 0.604'*'t E,A .|02 J.v 6 r3 0. Cyperus difformis (Cyperaceae) also formed a sudd colonization as did C. cephalotes. lt could be dis.tinguished from C. cephaìotes as having the tr¡querteous stem which can grow a height of 30 - 40 cm (Sewatabandhu, 1950) . The plants const i tuted 0.56'4 and 0' .27% in the Grass Area and in the l,Jeed Area respectively. The analysis of variance shows no significant difference between areas, but înd¡cates a signif icant difference (p( 0.01) over time (fa¡l e 29). Table 29. Analysis of variance on the distribution of Cyperus difformis :-,. (Cyperacaea) for the Grass Area (g) and the Weed Area (C). DF Sum of Squares Mean Square F-Value Area I 0. 009 0 .009 O.4BB T ime 5 0.282 0. 056 2.g26'tì< Area x 5 0.199 0.039 2.063 Res idual t .157 0.0tg 66 Eichornia crass ipes (Pontederiaceae) was found in masses which drift over the whole lake. Sometimes the vegetation was pushed together into temporary fíe'lds several hectares in area. Because there was so much of it, E. crassipes must be considered an important factor in the ecological structure of Bung Boraped. E. crassipes was found only in the l./eed Area and the percentage cover showed no significant change over time. Jussiaea repens (Onagraceae) is a floating aquatic herb, sometime creeping on land. The stem is round, shi ny and somewhat yel lowish green, with white or pink spongy bladder-l ike material at nodes. The plant commonly grows in still water and was found both in the Grass Area and the l.Jeed Area, nrostly along the surface of the water. The young shoot and leaf is edible and used as a green. There were no significant differences between areas or among times. The plant constituted a small fraction in both the Grass Area and l,/eed Area, 0.052 and 0 .02% respectivély. Coix aquatica (Graminae) is a very robust grass with tough stems about 2 cm thick and with trailing clumps of roots which can be over I m long. The plant was observed to colonise broad areas of the shore and, because the root clusters at the nodes were relatively long, in shallob, water there was no oxygen available in the entire water column. C. aquatica was observed only in the Grass Area. lts occurrence was detected only in February and March w¡th 0.07% of the total area. Differences among times were significant (p< 0.05) (Table 30). 67 Table 36. Anaìysis of variance on the distribution of Coix aquatica (Graminae) for the Grass Area (B) and the l/eed Area (C). DF Sum of Squares Mean Square F-Value 0. 040 0. 008 0. 148 0.002 Nel umbo nuc i f era and Nymphaea I otus (Nymphaceae) are cornmon along the shoreline area of Bung Boraped. The major difference between the two lotus plants is the character of leaf. The N. nucifera leaf usual ly rises up over the water vvhile the N. lotus leaf only floats on the surface of the water. !. nucifera was found only in the Weed Area (1.16% of cover) and N. lotus was detected only in the Grass Area (0.03|Z of cover). There were no s ignificant differences between areas or over time for either species. lpomia aquatica (Convolvulaceae) is a semî-aquatic herb, found mostly along the shoreline or near the edge of floating mats of aquatic hydrophytes. The plant is edible and commonly used as a green containing high Vitamin C. l. aquatica was found in both areas. lt constituted 0.22% in the Grass Area. There were no significant differences over time or between areas. Salvinia cucul lata (Ceratophyl laceae) was found only near the edge of the l/eed Area, associated with E. crassipes. The plant often forms sudd colonies wi th C. cephalotes or C. diffJrmis. Because ¡t i's commonly util ized as a substrate for other plants, i t must be considered important ín the succession deveTôþment. There 6B was no significant change over time. lt ranged in percentage cover f rom 5 .65% to 38.30%, with an average of l4.Bo'Á. Polygonum tomentosum (Polygonaceae) is a marsh or aquatic herb with a long and dacumbent stem which is nearly glabrous. The plant turns brown when old, and inside a mucilagenous material is always present. The plant was found in shallow parts of the Grass Area and constituted 0.84'Á of cover. There was no signif icant change over time. 69 .4. Invertebrates aSsociated with aquatic macrophytes Aquatic macrophytes provide habitats for spawning and feeding of invertebrates which in turn serve as food for fish. The species composition and abundance of invertebrates usual Iy varied with type. of aquatic vegetation and its influence. The rooted aquatic plants that emerged on the littoral are reported to be more productive in terms of number of associated invertebrates than are those floating on the submerged forms (McLochlan 1969 and Boyd lg71). Junk (197Ð reported in his study on the fauna of the floating vegetation in Bung Boraped that Eichornia crassipes was colonised by more invertebrates than lsachne globosa, Coix aquatica or Salvinia cucul lata. He also suggested that the bivaìves, which cons isted mainly of Scaphula pinna and LimnoÞera siamensis, were the most abundant both numerically and in terms of weight. He also pointed out that the fauna of the floating vegetation was richer in species than was the bottom fau na . 4.1 The fauna of the emergent grasses Planorbtdç¡- mainly lndoplanorbis exustus, occurred very frequently ::::: on Leersia hexandra, Hymenachne pseudoiterum and Cynadon dactylon. ,'.,'' The giant Piìa sp. (Rmpullaridae) was found to be abundant on Leersia hexandra. Invertebrate groups such as Ephemeroptera, Trichoptera, Coleoptera, and Diptera were present in large numbers. ;',:,:, :-. . Trichoptera and Ephemeroptera uJere associated exclusively with the bottom fauna. Trichoptera, which were widespread in the I ittoral area, were found bur.rowed into sunken grâss stems and occasionally grasses. also into the rootstocks of Chironomids were also observed : I::-': r, ! . '- a,,_l.' 70 w¡thin the cluster of grass roots. The mean number of inver- . tebrates for each handful of Leersia hexandra ranged from 0.61 to 46.1B vtith 23.!8 as an average. The other two major grasses, Cynodon dactylon and Hymenachne pseudoiterum, showed in,termediate numbers of associated invertebrates, 3.36 and B.lB per handful respectively (ra¡les 31 and 33). The mean number of invertebrates given here is based on the average number per handful sampled from vegetation species which occupied 25% or more of the surface area in the I x I m rectan- gular measuring frame. The number of invertebrates obtained in this manner will indicate the relative abundance of fauna associated with each major aquatic vegetation species, which in turn wi I I reflect the productivity of the area. 4 .Z The f aúnajf the f loat i ng weeds The floating weeds were found to be a favourable biotope for most invertebrates. Trichoptera, 0donata, Coleoptera, Hemiptera, Potamidae and Paleopteridae were widely distributed and abundant. lndoplanorbis 'éxústuq F. Planorbidae and Pi la Pol ica F. Ampul laridae were very abundant in the rootstocks of Eichornia crass ipes. Limnoperna Siáriránsis F. Mytilidae occurred very frequently in the floating particularly in Eichornia crassipes and Saìvinia cucul lata. . vegetation, Coleoptera were observed to colonise lsachne globasa, Cyperus cephalotes and Eichorniá cràssipes more heavi ly than Salvinia cucul lata. The crustaceans, mainly Macrobrach ium sintangense, Macrobrâchium rosenbergi i F. Paleopteridae and.Siamtfephusa paviei F. Potamidae, appeared to dominate the fauna associated w¡th E!:!grn¡" crass ipes. Copepoda and 0stracoda were found, but their contribution to the total biomass was 7L not significant because of their smal I size. The population density of invertebrates was highest by far in Eichornia crassipes with 21.06 n/handful . lsachne gloÞgsa was second wÎ th l3'06 n/handful ' Salvinia cúcul lata and Cyperus cgphalotes h/ere associated as a sudd comminity, and yielded 7.27 and 5.53 n/handful respectively (faUle 32 and 34). The number of invertebrates for each plant species appeared to vary over time , and depended on which vegetation__ I species was found to be in excess of 2i7.. Faunal densities varied among different places in a stand (center or marg!n of weed stand). The difference was very evident in the dense stands of lsachne globosa. The stability and structure of each weed species stand also salvïnia cucul lata gvp".;, inf!uences the abundance of fauna. "na oroo*i-tor. u ceptglgles were f requenrly bto*n "r*-ñ .r. t* short time, and then again pushed together. The structure of the stand was therefore very loose. The temPorary breakdown of the stand into:smal I clumps markedìy reduced the protection offered by the plants to the different animal groups. This could explain the lower abundance of invertebrates associated with Saìvinia cucul lata and Cyperus _cepha I otes . TABLE 31. The mean number and 95"Á conf i dence limîts of invertebrates per one handful found associated wÎ th some major aquatic macrophyte within the Grass Area (e). N9V DEC JAN FEB MAR APR MEAN't Leersia. hexandra 40.305 46.I8t 29.386 18.259 9.175 23.987 ro?01,, (l 9.821 - (zl.z9s- $ J66- (4.254- (l.gB¡- I .874) Bo.8l 9) 94.136) rioo .660) 69.232) 33.719) Hymenachne pseudoi terum 9.990 12.263 2.313 8. 188 (0.9r3- 90.992) Cynodon dactylon 4.419 2.313 3.366 (2.931- (o-g¡ .z3t) 6.htt) The mean values are based on the average number of organisms per detectable bíotope. \¡ l\) .::, .,, : :.:.,.. IABLE'32 The mcan nunber snd 95t conftdence llmlt of Invertebrstes Per one handful found assoclated wlth. some rîâJor aquâtlc macroPhyte wlthln the Vecd Arca (C). . NOV Dtc }1AY JUN JUL S EP I.ITAN {AN 8.994 .980 o.tto \.\73 9.044 | 3.060 I sachnc Alobosa _ t.998 3.157 5lr (0,0-24.5q3) (o.o-re.oe7),';lllãu, (o. o- (0.0- (0.0- , 2r2. rqB) 559.9261 | 52. \\7) Cyperus caphalotes 9.980 o.lrl3 2.999 1.687 r. a1t t.997 t6,\26 5,53t (o.o-r r4.767) (o' (0.0- (0.0- $.376- 1ã.,,,rl ¡9.581) 68,2291 50.69 r ) 27,\t7 | 21.067 Elchornla crasslpcs 2.529 7,827 7.\57 38.725 ,^ 9:?36 31.330 13. | 39 8'gsq | 7.83tl 1v.42 (o.o-39.oto)(1.59r- (1.77¡- (2 . oolr- (2.625- (t'Íål?orr, (0.1r74- (r.8or- (o.zz5' t5.5rt' 16.444) 26. l90) I 4. ¡6q) zzt,\62) "'iâ'.isrl I 34.703) 34.30q) 2]2.\961 5À4.009) 2\.997 7.277 Salvlnla cucul lata 3.039 l.lrq7 2.\72 2e0r ¡ 2,q27 2,\26 3.2t4 3.468 (o.o-35.855) (0.0-¡7. 614) (6.732- (0.0- (0. o- (0 .0- (0 .0- (o.09l- 72.)751 55 .280) | 5.988) t 4 .6¿r5) 3\5,56\) li.33r) { U) lålêËlltltr { æ mf :!e (¡t fr) 1¡{ F o \¡ -r.o,1rt À) r'{ â\-o -Þ. o- { o Hyt i I idae f (o .It ++++ + G' +{.+ + a ++. + Ampu I lar idae fl + + G¡ a + _{¡I Thaianidae a o -oc (Ð P lanorb ídae =(¡ o pstracoda .-_t¡ o lrl| ac topepoda a 6, =.o G, o Potamídae {l -3 Pa leopterar idae '-t.Cù G G¡.- (f- f a + 0l igachaeta €at o o + Ct f ì + Eph'cmeroptera Ø ('o + + + f ct + + + Trícfioptera l¡ + ¡ € + + + 0ãona ta f,' c, + -ct + + f c + + + Coleoptera êf, (¡ + f + + + Í)ã + + + Díptera o a : 'oo + j 0rthoptera û lî' , 9 Hemíptera ; û f,' G, 6¡ P I ecopter:a a tr 6 h Lep idopte ra f olìl Chaobor íd¿e @ :t. + ++' Ch i rononri dae ÍL :.:Ì^t'i.:-ì::-;.:.:: tÊli l;l; F|å Hli ri { Ëli q, r|¡- * ÞtD' rNU\¡\oou llrt ¡$f{- + + + 5\O È (> + o Hyti I idae { oÍ '+ Ìt ++++ + + c' .+++ + T ++ + t Ampu I l-ar idae + + (¡o î -à Tha ian i dae a ¡(t + ++ c f ++. ñt ++ f +r .+ P lanorb i dae o o + +. + -à + 0stracoda o . (|- .(|c + ++ a a Copepoda (D fo + Gl + + Potamidae o + f ?t G' Paleopteraridae i.- i (D + cr : I 0l ígochaeta CJ ul¡ + I + ct + q . €phemeroptera I il.. .. o + c| + .++++ + ; Tr íchoptera -+o ++ d. f+ 0dona tá f- + + :r + lD + +r Co I eoptera t c, ¡c + + + c, + +. ê + Diptera (¡ + 3 (¡c, 0 rthoptera I 'oo + f,- + Hem i pte ra øti, + + + + a P I ecop te ra Íd (D + 'o { Lep i dopte G} ra. 'o- + a |:¡ Chaobor i dar: CJ o Ch i ¡6¡s5i ¿¿. + çL j--i;.1.i.....j. '.:.ì1i;:I¡-.. :..:-:.;.'.: i': i: :-i:.1:. L . i].;-'.ii'¡:]:ì':::.ì.1-]::'.'::':'|::..::.¡:.:'.,1..::.::'.- 76 5. Benthos Data on the mean number and 95% confidence limits of the benthic organ i sms found í n the G rass _Area (B) , lJeed Area (C) and Open t'later Area (o) from November 1974 to December 1975 are presented in Tables 35 - 37 and Figure ll. The analysis of variance on the abundancesof each benthic group from the three different areas are presented in Tables 38 - 5ß. The bottom fauna in water bodies serve as an important source of food for fish. A knowledge of their development and species occurrence is important for the design of a fishery management program in a reservoir. Cowel I and Hudson (1967 ) cons idered water level fluctuations, depth and water temperatures as the major factors ínfluencing the distribution and abundance of the benth ic animal population in Lake Franci s Case, North Dakota. M¡ chael ( l968) reported that a large number of benthic animals in the littoral zone were associated with the presence of aquatic plants. Mclachlan (lgeg) found that the presence of rooted littoral vegetation in Lake Kariba, Rhodesia, caused an increase in the biomass of benthic fauna Studies on the benthic organisms of Thailand have been conducted by Laidlaw (1933), chiìton (1925), Fraser (1927), vejabhorge (l%7), Chujo (1941), Asahira (1961), Kawai (1961), and verna (1961). suvattii (lg¡8) has listed the scientific names of the aquatic fauna in Thailand and their distribution. Mizuno and Mor¡ (1970) reported in their hydrobîology survey in Thai land that Derel ia sp (Odonata), Baetis sp (Epòmeroptera), Hydrophilidae (coleoptera) were among the dominant aquatic insects in Payoa Lake and Nong Rahan Reservoir. Junk (1973) concluded that Dipseudopsis sp (Trichoptera), Eatogenia sp and Povi I la sp (Ephemeroptera) were the most frequent aquat¡c insects in the littoral zone of Bung Boraped. l,/aewngarm ( lg6g, 1970 and l97l ) , Sr isoowanatad (tgZO)' and Sunkagul (1971 an¿ lgTZ) reported on important benthic fauna in their hydrobiology survey of some major reservoirs in Thailand. They concluded that chíronomids always contributed more than 20% of ,,',.,,, '', those benthic organisms found. In this study aquatic insects appeared to be the dominant group, with more than half of the total numbers in all areas. 0l igochaetes were ,.,., : ' the second most irnportant and mo l l uscs the th i rd . Crus taceans r^/ere . :-:, ::.r the lowest in number collected, but they may not be an indication of numbers since the multiple corer is not suitable for collecting mobile crustaceans such as freshwater shrimp and crabs. l.l The benthic fauna ín the Grass Area (g) The mean number of benthic animals in the Grass Area was 1.25 n/core. lnsecta had the largest mean number of organisms, but this does not necessari ly indicate a greater biomass. D¡ptera larvae contributed the greatest number, pêÍticularly the Chironomidae which had a mean of 0.22 n/co,re. 0ther Diptera (mostly subfanri ry ,,.,,,,,:,,,, Dixinae and cul icinae) had a mean of 0.21 n/core. Ephemeroptera , ,"',' ''1 : t':: Trichoptera,0donata, coleptera and Hemiptera contributed to 0.07, ,:,:,' 0.02,0.03, 0.15 , 0.21 and 0.01, respectively. . ::'¿ 0ligochaeta had the second largest mean with 0 .25 n/core (slightly more than the Chironomidae). ,':,', Mollusca had the third largest mean with the pranorbidae averaging 0.13 n/core and the Ampul laridae 0.02 n/core. crustacea were collected in relatively small numbers with Ostracoda having a mean of 0.02 n/core and copepoda 0.01 n/core. :,,:',,: 78 ' chironomidae and 0l.igochaeta r"rere f i ., the rst to populate "' ìh" Gr"rr Area, in September soon after this habitat ù,ras establ ished af ter f lood ing in the raÍny season. Both groups v'rere usual ly present unti I Apri I when this area dried up. The greatest number of Chironomidae v,rere found in November. ;.,,... Kojak (1970)' reported that the formation of benthic conrnunities ; ¡n the Goczalkowice Reservoi-r on the River Vistula in Poland began with Chironomidae and 0l igochaeta, as they dÍd here. Diptera .1,, and Coleoptera þrere second in the formation. of the benthic conrnunity, ', : first appearing in October. Planorbidae fi rst appeared in December and ' . reached their greatest abundance in January. Ephemeroptera and 0donata first appeared in December and Ampullaridae, Copepoda and 0stracoda first appeared in January. ' l;2 Thg benthic órganisms in the_Weed Area '(C) imeannumberofbenth¡cánimals.intheuIeedA1eawas0.BBn./core. i The mean number for Chi ronomidae wasr0. l3 n/core, for the 0l igochaeta .0.l9 and for the' Ampul laridae 0. 13. Petr (1969) stated that- in shallow regions with abundant aguatic plants such as Pistia and Juss iåéa snails formed a substantial part of the biomass of benthos. Hollusca .: whichoccurredintheareawereUnionidae,Hyti|idae,Thaíanídae, Planorbidae and Corbicul idae. 0stracoda and the freshwater shrimp Paleopteridae occurred Ín small numbers. The freshwater shrimp Måcrobrachíum sintangense and Macrobrachium rosenbergi were almost exclusively associated with the floating weeds and r^rere. therefore col lected incidental ìy. Ephemeroptera, 0donata, Coleoptera and Chaoborinae occurred in small numbers. Tríchoptera were not found in the Ì,leed Area, '?o The Chironomidae population appeared to increase greatly after the floating weeds drifted away with the tropical storm in September 1975. They reached a peak ìn September (o.g: n/core) and then decreased slightly until December. This phenomenon suggests that low oxygen :: concentration under the floating weeds may have had a negative impact ,,, on the bottom fauna below. Ampul larídae, Planorbidae and Coìeoptera larvae also showed the same pattern as the Chironomidae. | .3 The benthic örgani sms in the Open l/ater Area (D) ,, , .t' The mean number of benth ic an ima I s in the Open l^/ater Area was ,,,. a: '1.42 n/core. The larvae of Chaoborus sp were encountered in the tt greatest number, 0.28 n/core. This insect larva follows the mobile plankton at night and stays close to the bottom sediment during the day. Additional sampl ing was conducted at night in order to understand the vertical distribution of Chaobolus sp. lt showed that the insect moved frorn the bottom to the I imnetic zone at n¡ght. :.. I TABLE35. The mean numbe.r and 95ß confldence llmlts of benthic organlsms In each core sample from the Grass Area (B). N0v 0Ec JAN FEB HAR APR SEP 0cT N0v ñça MEAN '' Ampul lar idae 0.059 - 0.059 0.166 0.027 (0-0.209) (0-0.209) (0-0.462) Planorbidae . 0. r89 . 0.059 0.585 0.059 0.096 0.189 0.335 0.139 (0-1.054) (0-0.209) (0-0.993) (o-0.209) (o-0.877) (o-0.8t2) (o-0.496) 0l igochaeta 0.303 0.t89 0.38t 0.189 0.335 0.493 0.059 0.603 0.t89' 0.262 (0-0rr0- . (0-0.584) (o-0.8'{o) (o.oz¡- (o-0.733) þ.tzi-- (o-0.209) (o-t.7t8) (o-0.599) 0.616) 0.433) 0.93q) 0stracoda 0.096 o. t89 0.o27 (o-0.363) (o-0.863) Copepoda -. 0.059 0 .006 (o-0.228) tphimeroptera 0.059 0.059 0.059 0.122 0.059 0.035 (0-0.209) (0-0.22t) (0-0.209) (0-0.33ó) (o-0.209) Trichoptera 0.059 0.122 0.060 0.060 0.029 (0-0.209) (0.0.336) (o-0.209) (o-0.209) 0dona tð 0.096 0.059 o.o5g - 0,t22 0. 033 (o-0.390) (o-0.22t) (o-0.209) aì ôco Co I eop te ra 0.122 0.335 0.381 0.230 0.284 0..059 0.122 0.152 (0- 1033 (0-0.537) (o:0.e77¡ (0-0.840) ) (o-0.537) (o-0.768) (o-0. zog) (o-0. 336) Dfptera - 0. 16l I . r 28 0.989 O.3lr8 0.059 o'.215 (0-0.'r76) (0.¡a4- (0.080- (0-0.209) (0-0.209) ¡.029) 2.596) Hemiptera . 0.06 I 0.059 0.006 (o-0.209) (o-0.209) Ch i ronomi dae 0.33rr 0,059 0.f89. 0.r89 0.272 O.O5g 0.230 0.757 0.303 0.225 (o-0.877) (o-0.209) (0-0.q33) (0-0.599) (0-r.459) (o-2.209) (o-0:537) (0.296- (o.orro- | .363) o.6l o) 0.885 0.643 | .794 2.253 2.023 | .9,92 0.1l8 o. 951 0.8t7 I.009 1.248 oco :"..: . 'ì ÏABLE The mcan nr¡rber and 36. 953 confldcnce ilmlts oi,rhc bcnthlc orionlrru ln thû trëed Arce (C) DEc (ro n.) (14 u.) Unlonid¡e - . 0.059 0.006 0'O0lt Corblcul ¡dêe (o_0.209) 0.050 (o-0.209 ) 0,122 0.059 o.ot8 0,0t7 (o-o'336¡ (o-o'2ôi) l{ytilldae 0,zJo / (0-t.0t3) o. 02 t 0,0 t5 Anpul lar.idae 0,122 0.t6t 0.t62 :. (o-0.491) (o-0.336) (o-1.075) - 0.599 0,260 0.303 (o-t.637) (o.05o- (o-0.i36) 0. t3t 0.092 Tha¡anldåo 0.059 0.059 0'560) (o-0,877) (o-0.209) - : o.ot2. 0.008 Plûnorbldae 0.585 0.272 0.059 . 0.345 0.1 22 0.4t8. 0.059- - 0.20t o.to9. ' 0.135 (0-2.r58) (o-ì.r59) þ-1.225, (o-t.t8r) (o-0.49t) (0-0.49t,- 9,!2?. (0-t.05q). (0-0.896) o. log ê ) to_o.eigl (0._0.209) 0 I ïgochðêtô i:: 0.301 . 0.70r. 0. I 89 0.565 o.z3o ' 0.349 0.058 ¡ . /^-^ (0-0.209) (0-0.568) (0-q.584) (o-0.552) . O.O6t ,r - 0.194 0.164 "Â41 (0'0. 95 tr) (o-o.zo9) (o-o:t62) 0¡ ! r¿coda - 0,058 . 0.058 - 0.t89 0'02l t:, (0-0. 209) (0-0.209) (o-0.599¡ 0.0t7 lj Paleoptcrld¡c 0. 189 0. t88 0.303 lô-^ qool 0.189 0 'l (0-0.599) (0-0,786) (o- 0.599) 0.015 '057 Ephlmcroptcrô ':: 0.059. - 0.272 0.030 0.022 (0-0.209) (o-0.8i6) 0dono !.r 0.059 - .r ^co 0.058 - 0.012 ( (o-0.^ lrz0) (o-0.2 0-0.209) 09 ) .0.0r1 Co I cop le ra 0.059 0. 058 0,260 o. t8g 0.058 O.122 0.055 (o-o,209 (o-0.582) (o-o,r'Z¡) 0.059 0.020 ) (o_0.209 ) (o-0.209) (0-0.204) (o-0.¡¡e) 0¡ ptcra 0.059 - -1 o. o5g 0.0t 2 0.012 (0-0.209) (o-0.2 09) Chaobor lnàc 0.058 . 0.096 0.059 0.059 0.334 0. t89 0.053 (0-0.377) (0-0,537) (o-o.qze) (o-0.733) (o-o.q¡¡) (o-0.209) 0.027 Chl ronomldac 0.059 o, t22 o. 058 o'830 (o-0.209 0,537 0.189 0.119 0. l0t ) (0-0.476 ) ' (o-o.zo9) (0. | 50- (o.09q- (o-0.r33¡ r .386) 1.2\3) 0.303 0.059 1.525 0.845 b.537 0,867 |,259 0.556 0.7.23 o.z3o 2.035 1,107 o.ee5 0.976 0.864 æ H 't'iìl : 'l ;1 .'.ll,.li, l ELt 37.lhc ncan number and 95? conftionce llmlrr of tho bÊnthlc orgonllnr In thc 6þen Uatcr Arc¡ (0) i DEc (10 n.) (14 ¡a.) Corblcul idûe .0.260 - (i.lB9. 0.t6ì 0.t22 0.096 - 0,122. - 0,059 - 0.059 0.0711 (o-0.682 ) (0'0'r'62) (0-0'336) (o-o'377) Àñpul ì¿.ldðc - ";:::;" "-::ï' :-;:;ä: l ¡,iii] 0.!6, ,.,,, 0..7s7 o. 195 0. t57 (0-0.20e) (0-0.209) (o-0.¡,62) (o-0.539) (o:ò.aIo) (o.iói:' {o.tií_- Th.lian¡dùe t.773,1. | .803) 0. - 0.059 006 0,00rl Plðnorbldæ 0.059 ' - (0-0.53?) r o.qrs - o.o5e o.r8e o.o5e. 0 ,olt l 0. c25 6-3:lå1t' (0-r.534) (0-0.209) (0-1.075) (0-0.209) 0l lgochoeto 0.38r 0.203 . . ' 0.059 - b.13rt. 0.704 1.849 0.712 0.366 0.688 o.o59 0.201r (o- t .2tr7) (0-0.20e) . 9.096. . . . o.3rr{ 0,160 (0-o.2oe) (o-0.377) (o-o.si¡) (0.r37-r.55e¡ (0.!79: . (o.oiö:- (o-i:óti) to:i.eizl fo-i.óíjl to_õ.liãl 4'419) 2'ooq) 0s t rôcodù - 0.059 - (0-0'20e) 0.039 o.oag ro9¡lï3,r ro-3:!å3r r'-3:l8ir Copcpod¡ 0,059 - 0.059 (o-0.269) (0-0.209)' '0.012 0.008 Pô leopterldåe (0-0'20e)o' 058 0.003 0.0t2 o.ot3 Po!ômi doc to-3.!33r r,!¿llür r.-3:!å3r tphlmcroptcrô - 0.122 o. t22 0,122 (0-0.34e) ' 0.029 (0-0.336) 1o:ó.ãõs) lrl choptcr¿ - 0,122 ' o.oo8 (o-o 0.'otz, ' 3'r9 ) 0dono tà - 0. I 22 0.058 0. t 89 o,tzz 0'Olll (0-0,3q9) (o-0.209) (0-0.¡'33) (o-o.rtgt) 0. O¡ I Col cop te ra - 0,231 , 0.335 - O. t22 0.059 0.051 (0-0.58") ' (0.050- (0-0.336) (o-o:ãó¡') 0,orrlr o,665) Henl ptera 1 - 0.13! . (0_o.r¿S) - { .0.059 v, vJ) , (0-0.209) 0.025 Dlptéra - 0,998 0.260 0.059 - 0.189 (0.'f:,,35)(o-0.322) ô rno (o-o.zôg) ro-o.ráíl ' 0.097 g. I oo ro:òjií¡r ,09;îi3rl rJóll!,l . Chðobor I dðc 0,122. o. r89 t.174 t" il7 0.335 O.t8g 0.303 0,058 0.t22 (0-0.336,. (0-0.643). (0-0.568) . (0-0.t'33). . 0.122 o.oçe 0.23t 0,29r (0.29qá. (o.0to-. (o-o.rr33¡ (o-0.!g!) (o-0.376) to:ò.lill to:ö.ãógl 2.rr90) 0.733) Chlronmld¿o 0.05t - o.r'07 . g.9l?. 0.463 . 0.520 l:?!,, o,r9e o,t0l 0.JJ8 (0-0,20rr . (ll0ll:.,.2'-?12 (0,021-.. .0.t22_. 0.ts9 0.t77 t (0-t¡'015) (o-o.2ol) (o.rjo-.. (o-r.316) (0.0.q26) (o-o.e'O) to:ó.¡5¡l--'' to.ííõl 0,896) 4.053) 2.00rr) o,dq¡l 0.759 0.38¡t 2.\71 0,896 t.6t5 ¡,l3t 0.761 2.09t 5.t2e 7,\57 r.tro 2,007 t,?09 t.9ol 1.41g 1.759 æ l\) i.' .. .': 1; :.i ,,.,:¡. ": .: :. i:. ..:,:, - - .'l_f f'a j.-,' i- : :.: Figure I I . The development pattern of some benth i c organisms with respect to tirne in the Grass Area (a), the Weed Area (C) and the Open Water Area (0). ::..': l B3 t¡::=:lBtl I o'...... '.'....(c) I tol la_ I CORBICULIDAE PLANORBIDAE .o. ..u! o... OLIGOCHAETA "t 075 o50 o to COLEOPTERA Lrl E. C)oo \ 1.128 t IJ co 05 ¿. zof t.o t.t74 o.5 2.222 CHIRONOMIDAE 05 q, o DJ l- tvl 1.4 The quantitåtive analysis of benthic fauna density differences among the Grass Area (B), the Veed Area (C) and the Open \,/ater Area (O) . In al I three habitats Diptera ìarvae (mainly Chironomidae) were _ numerical ly dominant over the enti re study period. 0l igochaeta were present very f requently and were considered as important as Chironomidae. ,..1 ..: The Grass Area and the Open l,/ater Area were found to be the richest in numbers of benthic organisms, 1.25 and l.4z n/core respectively. The l,Ieed Area was lowest with 0.BB n/core. 1.4.1 Unionidae Uniónidae were found only in the l,/eed Area in September. HVriöÞsis delaportei and Hyniopsis bialatus were the most frequent. 0nly sma I I immature clams were col lected. Mature clams were probably missed because the opening of the Multiple Corer was too smal l. The analysis of variance shows no significant difference among areas or overa time. | .4 .2 cóib i cú I idae Corbicula siamensis appeared to be the dominant species. corbicul idae was col lected only from the Open l,/ater Area and the vleed Area. The analysis of variance shows a signif icant d ifference (p ( 0.01 ) among areas because Corbicul idae was absent in-the Grass Area. There wâs no signif icant difference among times (ta¡le38 ). l;jj:r:ìi::,.::,.:. t.t:l 85 Tab I e 38. The analysis of var¡ance on the abundance of Corbicul idae among the Grass Area (g), the Weed Area (C) and the 0pen hrater Area (0), excluding the dry nnnths Hay - August 1975, :.- Sou rce DF Sum of Squares Mean Square F-Value ;k:t A rea 2 o.3zt 0. t60 7 .735 I tme 9 0.202 0.022 t.0Br Area Time lB 0.617 0.032 t.648 Res i dual I 50 3.120 The mean number of Corbicul idae in the Open Water Area was significantly greater (p ( O.Ol) than that in the Weed Area over the period of I 4 months (raUl e 39 ) . Table 39 . The analysis of variance on the abundance of Corbicul idae for the l,/eed Area (C) and the 0pen Water Area (0) over the period of 14 months, including the dry months May - August 1975. Sou rce Sum of Squares Mean Square F-Va I ue Area I 0.248 o.2\B 7.764"" Time r3 0.524 0.040 1.259 Area x Time l3 0.596 0 .045 1.433 Res i dua I 4.482 0.032 g6 i:' 1.4.3 Hytî I idae Lygjnoperna siamensis was the dominant species and found only in the Weed Area. lt numbered 0..23 n/core Ìn September and averaged only 0.01 n/core for the entîre period of l4 months. Junk (1973) reported that Lymnoperna siamensis bras seldom found in the bottom fauna of Bung Boraped, but it occurred i n the f loat i.ng vegetat ion I .4.4 Ampul lar idae Pila ampullaria rvere abundant in all three -U¡>o]* "nd habitats but were most abundant in the 0pen llater Area (0.ì9 n/core). Abundance was second greatest in the V/eed Area (0.13 nlcore) and least in the Grass Area (0.02 n/core). The . analysis of variance shows a significant differencu (p (0.01) among areas, wîth areas D and C higher than B. There is also a significant difference (p(0.01) among times. The Amputlaridae .l tended to increase $heîr populatîon during the hîgh flood period Septembei - December 1975. The interaction betwegn area and time is also s ignif icant (p ( O.ol) (raUl e 40,and ¿1). The inter- , pretation for interaction fol lows. The Ampullaridae were collected in the Grass Area only during January, March and April. During these months the establirnua grasses were still growing and there was I ¡ttle decomposition. In area D the snaiìs gradually ¡n"r."red theìr numbers during the high flood period, from ---l-, in December' 0.lB n/core in septeinber'to the peak,:f 0.94 n/core 87 Table 4d The anal ys i s of variance on the abundance of Ampullarîdae among the Grass Area (g) , the l^/eed Area (C) and the Open t/a ter Area (o) , excl ud i ng the dry months I'fay - August 1975, Sou rce DF Sum of Squares Mean Square I F-Value Area 4 I.4t3 0.706 g.897o" -i--u I tme 9 5.01B 0.557 7.808"" Area I lme IB 5.372 o.2gB u.vgxn R9s i dua I 150 10. 7l I o .071 Table-41. The analysis of variance on the abundance of Ampullaridae for the Ueed Area (C) and the Open ilater Area (O) over the period of 14 months, including the dry months May - August 1975. Source Sum of Squares Mean Square F-Value Area I o.284 0.284 3.72\ " I tme t3 9.26\ 0.712 9.31 4" *lc Area x Time t3 t.948 0.r49 | .959 Res i dua I r40 t0.7t I o.076 ì!, - 88 | .\.5 Tha ia ni dae Melansides tubuculatus was the dominant species and, was,found in the Weed Area and the Open l,Jater Area. Thaianidae occurred only in small numbers in both areas, at 0.01 n/core in area C and 0.01 n/core in area D. There were no significant differences between areas or among t imes. l.\.6 Planorbidae Hippentis umbil icatus was the dominant species and þras uniformly distributed in al I three areas. Planorbidae were encountered in the greatest number in the Grass Area w¡th 0.13 n/core. The lJeed Area had the second largest number, 0.10 n/core for the period of l0 months and O.l3 n/core for the total of 14 months (¡'tay - August included). The Open Water Area had the lowest mean numbers, 0.04 n,/core for the period of l0 months and 0,02 n/core for the period of l4 months (¡'tay - August were included). The analysis of variance shows a significant differencu (p (0.01) among times, with a peak of abundance in January. An interaction was not found and there uras no difference among areas (raul e 4;). Table 42. The analysis of variance on the distribution of Planorbidae amo.ng rhe Grass Area (n), the Weed Area (C) an¿ the Open llater Area (O), excluding the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Value A rea 2 0. 510 0.255 2.541 I lme 9 2.604 0.289 2.879 Area I tme t8 2.635 0.r46 t.\56 Residual 150 15.07\ 0. 100 B9 1.4.6 ol igóchaéta Aulocátus fúrcatus, Páuanais litteralìs and Dero obtusa (F. Naididae) occurred very frequently throughout the three areas. There was no sîgnificant difference among areas but there was a significant difference (p (O.Ot) among times and a signif icant (p(O.05) area x time interactíon (Table 43). There were two major peaks. of abundance, the f i rst .in January i n the G rass Area ancl i . 'the the lJeed Area, ano The secondi in October ¡¡ iGras: Area .,1,,.i,::" and the Open Water Area. TIris pat-tern-.couÌ.d,,explain the interaction 't '' -t: and may suggest that the removal of f loating weeds (which in turn 't"' increases the oxygen content at the bottonr in the \,Ieed Area) does not benefi t the 0l igochaeta. The on the abundance of 0l igochaeta Table 43. analysis of variance amo.ng I the Grass Area (E), the l{eed Area (c) and the Open l,/ater Area (o),excìudingthedrymonths|1ay-ounu,.|975. Sou r Sum Mean Square F-Value ':.. ce DF of Squares A rea 2 0 .210 0. t05 0.593 v, -t-" I lme 9 3.306 0.367 2.07tî A rea x Time IB 6.258 0.3\7 I . 963'* Res idua I r50 26.567 0.177 The analysis of variance for the Weed Area and the Open l'Jater Area over the entire 14 months showg that there was a significant difference between areas (p ( O. Ol )- i nteract i on between area and t ime (faUl e 44) . The mean number of 0ligochaeta per core per month in the open l'later j.i::.1 i,::r::!. 90 Area was 0.36 and in the I'leed Area 0.16. The abundance of 0l igochaeta fluctuated over time, and the pattern was different in the turo areas. l,/hen the number of 0l igoc_haeta in the Open Water Area reached its peak in July and October the 0l igochaeta in the l.feed Area dropped to the fowest level. This pattern showed no apparent relation to 0, concentration. Table 44. The analysis of variance on the abundance of 0ligochaeta between the Weed Area (C) and the 0pen l^/ater Area (O) over the period of .:.,... 14 months, i nclud i ng the d ry months May - Augus t 1975. ..,:,.'.¡ Source DF Sum of Squares Mean Square F-Va I ue : Area I 2.023 2.023 g.467"" I tme t3 6. il5 0.470 2.201 .L.L Area x Time t3 I1.93t 0.917 \.294"" Res idual r40 29.920 0.213 | .4.7 0s tracoda Ostracods were found in al I three areas. They were lower in abundance ,.; , than many other organisms but the number of 0stracoda collected may ' not be a true representation. The analyses of variance showed no significant difference either between areas or among times. | . 4.8 Copepoda Cyclop: sp. is distributed throughout Bung Boraped and other reservoirs in Thailand, and in this study was collected in the Grass Area and the Qpen Water Area but not in the l,Jeed Area. lt was collected in very device may be small numbers, although again the unsuitable sampling ,, o1 responsible. There were no s.ignificant differences either between areas or emong times. 1.4.9 Palèopteridae Macrobrachium sintangense and Macrobrachium rosenbergi were aÍìong the freshwater shrimps found in the l,Jeed Area and Open I^/ater Area. They were found twice in the Weed Area and only once in the 0pen lJater Area, and not at all in the Grass Area. However, the analysis of variance indicated a signif icant difference among areas (p<0.01). The area x time interaction (faUle 45) was also significant (p<0.01) which suggests that the freshwater shrimp were almost exclusively associated with the floating weeds. The shrimp disappeared after the mat of floating vegetation was washed away by the tropical storm in Qctober. Macrobrachiuqr sp have been long known to favor the floating vegetation biotope (Suvattï l93B; Mizuno and Mori 1970; Nimsomboon and Tongmee 1970). Table 45. The analysis of vari"n"" on the abundance of Paleopteridae among the Grass Area (a) , the l'Jeed Area (C) and the Open Water Area months May ' August 1975' (O), excluding the dry , DF Sum of Squares Mean Square F-Value Area 2 o.096 0 .048 \.285 I ¡me 9 0.192 0 .021 | .004 Area x Time r8 0 .384 0 .021 t.904 Res i dua I .',.:': 'i.: -:', 92 1.4.9 Potamidae Siamthèlphuse paviae was the dominant species and observed only in the open lJater Area during october and November 1975. lt was in very smal I numbers. The analysis of variance shows no sígnificant differences. The Potamidae was cited by some Thai fishery biologists (Nimsomboon and Tongme, lgTO and Potipitak, 1970) as being very abundant in Bung Boraped. Again, the sampl ing device may not have been aPProPriate. I .4. l0 EÞhérÍrèroptera Mayfly nymphs were found widely distributed in all three areas.. There uras approximately the same abundance in every biotope, 0-04 n/core in the Grass Area, 0. 03 n/core in the l.leed Area and 0 .03 n/core in the gpen \.later Area. There was no signif icant differe.nce either among areas or times. The Ephemeroptera nymphs occupy an important place in the economy of aquatic communities. They are practical ly defenseless and are preyed upon by nearly every aquatic predator. Usinger (1963) stated that mayfly nymphs are highly selective in their habitat and each species has its own time of emergence. Junk (1g73J reported that Eatogenia sp. wês particularly significant in the bíomass of the He also concluded that Eatogeniq sP. . bottom fauna in Bung Boraped. preferred the fine sedirnent, but not rotting detritus, and that its emergence was approximately January to September' l.4.ll Trichoptera Caddis fly larvae occurred very frequently in the Grass Area and just once in the Open l^Jater Area, but not in the I'leed Area. There was a s ignificant difference among areas (p (0.01), but :.. -r-: o? no d¡fference among times or interaction (faOle 46 ) . A majori ty of the larvae collected were net-spinning forms, tube-making forms or purse-case-makers. Table46. The analysis of variance on the abundance of Trichoptera amo.ng the Grass Area (g), the Weecl Area (C) and the Open h/ate, nr." (D), excluding the dry months May - Augus t 1975. ' Sou rce DF Sum of Squares Mean Square F-Value .:.: tl' A rea 2 0.050 o.025 3 .064'k I tme 9 0.08r 0.009 1.093 Area x Time B 0.2\2 0.0r3 r.630 Res i dua I r50 1.241 0.008 | .4. l2 Odonara The mean number of Odonata was 0.O3 n/core ín the Grass Area, 0.01 n/core in the hleed Area and 0.04 n/core in the Open V/ater Area There was no significant difference among areas, and no interaction or difference among times. Gomphidae, Coenagrionidae and Aeschinidae brere êmong the most common taxa found. Most of these dragonflies and damselfl ies develop in permanent freshwater. The naiads are important to fish and other aquatic însects as food. The naiads of the Gomphidae were observed to burrow into the mud. 1.4. l3 Coleoptera Coleoptera were distributed over the entire area of the study with greatest numbers in the Grass Area (0.15 n/core). tn the lJeed Area and the Open Water Area the mean densities were 0.02 ::ì'.::ì '.i :.1 94 n/core and 0.04 n/core respectívely. There was a significant difference (p( 0.01) among areas (raule 4z). There was no interaction between area and time, or difference among times. Table 47. The analysis of variance on the abundance of coleoptera among the Grass Area (g), the \./eed Area (c) and the 0pen l,/ater Area (O), excluding the dry months Hay - August 1975. Sou rce DF Sum of Squares Mean Square F-Value Area 2 0.897 0.448 9.237 I tme 9 o.789 o .087 r.804 Area x Time B 1.426 0.079 1.631 Res i dua I 150 7.286 0 .048 s The analysis of variance between the l'/eed Area and the Open þ/ater Area for all l4 months showed that there was a signif icant difference (p( 0.0ì) :.:.. among times (faUte 4g). The distribution appeared to show three major i't,, peaks. The f irst was during and February, the second in July _January '...,,. and August, and the third in November. This sporad¡c pattern., ¡f not caused by some,environmental factors which the author could not identify, should indicate some I ife history characteristic of the r',., :_-:. water beetles such as the emergence periods. iÈ:'::-:..:j?r,:,i |': 95 Table 48. The analysis of variance on the abundance of Coleoptera for the Weed Area (C) and the 0pen ly'ater Area (O) for the period of 14 months, including the dry months May - Augus t 1975. Sou rce S1m of Squares Mean Square F-Value ,Ot A rea I 0.0002 0 .0002 0 .007 T ime t3 1.563 0. 120 3.557 Area x Time t3 0.577 0.014 1.3t3 Res i dua I r40 4.733 0 .033 sabrosky (lgsr) stated thar 5,000 species out of 277,000 species of beetles which have been described are aquatic. Leech and Chandler in Usinger (1963) reported that in the Nearctic region alone there are ten famil ies in which both larvae and adults of virtually al I species of Coleoptera are aquatic, three in which at least one stage is aquatic, and two in which the larvae occur in water or on the under- water part of plants. In Bung Boraped most of the water beetles are found either burrowed in the mud or attached to the lower stems of the submerged or emergent vegetation. I ..4. l4 Hem i p tera This group was observed only twice, in the Grass Area and the Open l/a ter Area. The occurrence Ì^Jês i n the range 0 .05 - O .06 n/ core í n the Grass Area, and 0.05 - 0.33 n/core in the 0pen water Area. The analysis of variance from both tables (among the three areas with May - August excluded and between the l,/eed Area and the Open Water Area over the entire l4 months) showed a significant (p (O.Ol) difference among areas and among times, and also a significant inter- ;:lì 96 action (Tables 49 and 50) Table 49. The analys is of variance on the abundance of Hemiptera ",ilong the Grass Area (e), the l^/eed Area (C) and the Open l.,fater Area (o), exc I ud i ng the dry months May - August 1975. Sou rce Sum of Squares Mean Square F-Value Area 2 0 .082 0.04r 5.740 T íme 9 0.294 0.032 4.s47 Area x Time t8 0.637 0.035 4.gtl Table 50 . The ana lys is of variance on the abundance of Hemiptera for the l,Jeed Area (C) and the Open l^/ater Area (O) over the per iod of l4 nronths, including the dry months May - Augus t 1975. DF Sum of Squares Mean Square F-Value Area I 0.05 r 0.05 t 8.lBr"" .t -L T ime t3 0.469 0 .036 5.734"" Area t3 0.469 0.036 5.734xx Res i dua Usinger (tgZO) reported that l6 famil ies of Hemiptera occur in, on or near the water. These include the water boatman (Corixidae), back swimmer'(ltotoneit idae) and Water Scorpion (Nepidae). He also :.:l 97 stated that the Hemiptera are predators at'an i ntermed iate stage i n the food chain of their respective communities. The Cor ixi dae are ç partly responsible for the prîmary conversíon o I plant material i nto an ima I food . 1.4. l! DiÞtéra Diptera are a large and diverse group of insects. According to Peterson (lgSl) fully half of the species Iive in water. tr¡rth and Stone in Usinger (tgZO) indicate that the var¡ety of habitats occupied by the immature stage of aquatic Diptera is perhaps greater than that of any other order. D¡ptera such as midges, crane fi¡es and brine flies often occur in sufficient quantities to be very important food i tems for f i sh. (") General Diptera (exclusive of Chi ronomidae and Chaoborinae) . The groups found consisted mostly of Cul icinae (mosquitoes) and Dixinae (0ixa midges) F. Cul icidae. They were found in greatest number in the Grass Area (0.210 n/core). The 0pen l'Iater Area was second (0.09 n/core based on l0 months average excluding May - August, and 0.10 n/core for the 14 months average) and the l^/eed Area was lowest (O.Ot n/core and for the l0 month period and 0.03 n/core for the l4 months period). The analysis of variance for both tests indicated a signif icant difference (p( 0.01) both among areas and among times, and the interaction (faUles SJ and 52).. The peak in the Grass Area which occurred during February and l4arch; extremely high. There were two peaks in the 0pen l^/ater Area, the f irst in January and the second during June to July. 9B Table 51. The analysis of variance on the abundance of Diptera among the Grass Area (g), the Weed Area (C) and the Open l.later Area (O), excluding the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Va I ue .::.:: :.. : : Area 2 2.024 ¡ .012 17.176"" -r- -L" ltme 9 5. 180 0.575 9 .768" Area x Time l8 7 .307 0 .405 6. BB9'*"- Res i dua I r50 B. 83B 0.058 Table 52 The analys is of variance on the abundance of Diptera for the l'/eed Area (C) and the Open V/ater Area (D) over the period of I 4 months, including the dry months May - August 1975. Sou rce DF Sum of Squares Mean Square F-Va I ue Area 0.3\7 0.347 9.\53' -L -r- Time t3 2.523 o. r 94 5.283"" Area x Time l3 | .372 O. 105 2.814""' Resiciual r40 5.141 0.036 (b) chaoborinae (r. cul icidae). The bentho-planktonic Chaoborus sp.was very abundant in the Open l'Jater Area. I ts mean dens i t i es con- st¡tuted 0.28 n/core over the l0 month _ period and 0.25 n/core over the entire l4 months, or- one fifth of the total number of organisms. Chàó.bo.ru.S. sp.was a I so found wi th in the l/eed Area, but the specimens 99 were collected close to the 0pen Water region and might be due to an edge ef fect. l,lo Chaoborus sp. u/ere found in the Grass Area. Areas were significantìy different (p< 0.01). There were also significant, differences (p ( 0.01) among times and a significant interaction (table 53 and 54). The population of Chaoborus sp. in the Open Water Area appeared to expand very rapidly and reach its highest peak during February and March while the population in the Weed Area remained quite stable at a low level. The density of Chaoborus appeared to decline over time, particularly during theflood. This might suggest thé biological cycle.anú'emergence of ímagines. - Table 53. The analy^sis of variance on the abundance of Chaoborinae among the Gráss Area (B), the I'Jeed Area (C) and the 0pen Water 'Area (O), excluding the dry months l4ay - August 1975- Sou rce DF Sum of Squares Mean Square F-Va I ue " Area 2 4.699 2.349 44 .458" :k;k T ime 9 5.295 0.588 il. r31 Area x Time IB B.t 62 0.t+53 8.579 Res idua I r50 7.928 0.052 Table 54. The analysis of variance on the abundance of Chaoborinae for the Weed Area (C) and the Open tr/ater Area (D) over the period of 14 months, including the dry months May - August 1975. 100 DF Sum of Squares Mean Square F-Value -L -r- Area I z.4gl 2.t+97 32.952"" -r-.L I tme t3 8.61 I 0.662 8.Bl1"" .r- -L Area x Time t3 6.457 o'4go 6.602"" Res i dua I 10.533 (c) chironomidae. chironomus sp. is widery distributed in Bung Boraped. lt occurred in the Grass Area at 0.22 n/core, and in the Weed Area and the Open Water Area at 0.14 and 0.17 respectively. The analysis of variance for all three areas indicates no significant difference among areas, but there was a significant difference among ! times and a signif icant inreraction (p< 0.01) (raule 55). The popula- tion of Chironomidae with';n the Weed Area during the f ¡rst six months appeared to be very low, but an increase in numbers uras very evident after the mats of float¡ng weeds had drifted away because of the tropical storm in September. This indicates some improvement within the bíotope, possibly increased oxygen concentration. The densities of Chironomids in the Grass Area and the Open Water Area appeared to fluctuate over time with some sporadic peaks. The populat¡on of Chironomids within the Grass Area reached rits highest peak during period. the high'f' flood lJeed removal initÎated the increase of the Chironomidae population in the.Weed Area, which did not occur in the other two populatíons. 101 Table 55. The analysis of variance on the abundance of Chironomidae among the Grass Area (B), the Weed Area (C) and the Open \./arer Area (o), excluding the dry months May - Augus t lg75 DF Sum of Squares Hean Square F-Value A rea 2 0.3r8 0. 159 t.qe T ime 9 5. l98 0.577 6.o7s Area r8 5.069 0 .281 2.962 Res i dua I The analysis of variance for the Weed Area and the 0pen Water Area over the entire l4 month period showed that the Chironomidae population in the 0pen Water Area was signif icantly higher than that in the ì¡/eed Area (p < 0.01). Times were also signif icantly different (p< 0.01) and the interaction was significant as wel I (Tabìe 56 ). The population of Chironomidae varied over time and reached the highest peak during the period of lowest water level (June - August). The population then dropped suddenly in September as v',ater flooded into the reservoir, with pH at 6./, 0.¿-¿ at 3.0 ng/l and C0. at 16.2 mg/ I (fable 9). Tabìe 56. The analysis of variance orì the abundance of Chironomidae for the lrleed Area (C) and the Open l.Jater Area (O) over the period of 14 months, including the dry months May - August 1975. ì:i'::i [.:.: LO2 S1m of Squares Mean Square F-Va lue Area I 2.902 2.9O2 29.745 tfme t3 I I .040 o .849 8.702 Area 13 12.043 t.003 t0.28t Res i dua I t3.661 o.097 r:.-ri: ,.. .. ). '.. ::.- . 103 6. Fîsh Relative Abundance The gill nets used in this study consisted of a belt of three different mesh sizes (3,5 and 8 cm). The data for the number of fish caught by electro fishing, in which each fishing period was limited to a l5-minute run, were also used to assess the relative abundance of compressed form fish which were not effectively caught by gill netting. Fish landing stat¡stics for Bung Boraped in the period 1974 - 1975, and the species composition, are presented in Table57. The mean weight of fish caught by experimental g i I I nets f rom the Grass Area (g) , the t'/eed Area (C) ancl the Open VJater Area (O) for each month are presented in Tables 59 and 59. The number of fish caught by electro fishing and by experimental gill nets, with species composition, is presented in Tables 56 and 61. Small fish that were too small to be taken by a 3 cm net were not investigated. Most of these fingerl ing fish are of no commercial value, except for the two aguarium species Labiobarbus bioolour and Datnioides mi crol epi s . Taxonomic studies of tropical Asian fishes have been made by a number of icthyologists, such as Ì,Ieber and Beaufort (lgl0) , Fowler (lgZ4-lg), Smith (1g45), Suvurtei' (lgSo), Th¡emmedh (lgOO) and others. swingle (l g7o), Shel I and Lovel (1972) reported on the inland fishery situation in Thaiìand during 1966 1971. Tongsanga and Kessunchai (1964) considered ecological aspects and quantitative fishery stat¡stic for Sri Ayuthya Provine, in the central part of Thailand. Sidthimunka (1973) presented the length-weight relationship of the freshwater fishes in Thailand. Mizuno and Mori (1970) and Junk (1973) presented some observat¡ons on the fishery of Bung Boraped. According to Thiemmedh (1966) 1,061 specíes of fish have been described in Thailand, compared to the 550 species reported by Smith (t945). N¡msomboon Ít-a -" LO4 (1969) repor ted 73 spec¡es of f ish in Bung Boraped. suraswad i (1972) ,'.'' concluded from his study of the fish population of Bung Boraped, using tagging methods, that there were approximately 30 - 37 nillion fish weight 1,000 - 21000 ton in the reservoir before the draining and open-fishing period in lg7l, l{aewngarm (tglS) reported, f rom his post-water draining investigation ...-:,t,,1,, in Bung Boraped, that 84 species of fish were observed frequently, and among these carp constituted 40.417o, catf i sh 26.50'Á, murrel s 6.\47., and miscel laneous 26.657.. He also concluded, based on rotenone sampl ing, that the overal I stand- ,, ,.,, ing crop of f ish in 1972 was approximatel y 69.124 kg/acre. Anonymous (197Ð "';;"' : ,'...:-:lt- stated in the Nakhon Sawan Fishery Annual Report 1973 that the populations of ""'-' four species of fish,OphÌcephalus striatus, Anabas testudineus, Trichogaster pectoralis and Clarias batrachus increased but that the populations for the other species, !Jállagonia attu, Kryptopterus bleekeri,0phicephalus micropeltes and Waìlagonia dinema, declined after the water level manipulation in 197.|. reports,from Fishery According to the statistical .the,$lakhon 'Sa.r¿an ltation (lg16), 148 specíes of fish are found in Bung Boraped and its tributaries, and a total of 723,048 kg of f ish r,tvjere caught Table 57. PercenË specíes comPosition of fish Ín Bung Boraped, October L974 ' ,L975. FISH SPECIES [A]¡D I lfc : SPECIES -_ . (ts) coltPos¡T¡0N I osteochilus hasseltii .. ll3rT1g 16.224 : 2 ' ophicèphaljrs srr¡årus .. ,: 76:801t 10,626 'ciup*oia"J t Jrl'r7i, ¡ Çs"tororn" ;.u;; lr . Lab¡obarbusil iniatus . . ...,' -51 ,OOO l.O5j ' ' ' t!.gzb - 6 Ophìcephalus nicropelres 4zr84O ' .r " ' 7 Puntlus gonionotus kZ,SSg I.8Bg å2,008 5.808 .'."'. -'- . 9 Ophicephalus lucius ': " .34,.662 4.llg .' ¡O Gyclocheìlicchys enoplos ":' . n,79A 3,15I ':'lo.ttà?ìõ ll l¡ctop.terus noÈopterus - : .llrs7t+ 2.568 :- . lZ Glarla's batrachus .. . : t6,tt66 2-277 1. '. . ¡3 0xyleotr.is ri:ar¡oratus 16,\36 Z.Zll .. . l4 Fluta alba 13,006 -l.7gg 15 Anabai testudineus 1?,1616 1.7\j '' , - ¡6 Trichogasrer pectoralîi ' t2ro50 1.666 'l-45+ - l7'.Horulius chrysophekadíon - 10,520 : ; :- 19 Puntïopl i tes proctozysron . :' . . '61394 t.884 - ' ZA Trich.ogaster trichopterus , '. 5r5OB - 0.76¡ 2l Chand+ ¡rolfi i , , --' : .. - 23. Hanpala macrolepîdota .. , ' 2"' KryPtoPterus bleekeri : ' Z5 þc¡.ognathus aculeatus 31090 . O.4Zl ' 26 Pangassìus su. ichì 21316 oåza : 27 Pseudc¡seiaena s.oldado .- irO5o 0.283 ': . 2B Uaflagonia attu lr9l8 0.?65 29 Datnioîdes nÌcrolepis. .: l'50+ A.2O5 30 Osteochi tus telanopleura. lrlt?O 0.196 3l Hal lago dine,ns 1,?.62 -0.f74 32 Pseudosclaena soldado I'l 18 O.¡5IÌ 33 0sphronernus Sorarny 97A O, ¡¡tt 3\ Gìrrhinus nícrolepïs 932 O-¡28 35 Pangasíus þrnauciî ¡ 888 ' O-lzz 36, Hiscel laneous 38,876 5.376 :' Total 723,O\B 100 '.,1 106 6.t Fi sh fauna of the Grass'Area Nineteen species of fish were caught by the exper¡mental gill nets duríng November l97l+ - December 1975. Trichogaster pectoral is were greatest În number at 23.942. TrichógaSter trichopterus and Anabas testudineus were the second and the third, at ì8.30% and 15.\9'/,. Amblyrhynch ichthys truncatus ,. and LucioSorna bleekeri ranked fourth at 7.54%. However, electro f ishing obtained 27 species of fish from the Grass Area. Ophicephalus lucius made up 19.762 and pectorslis , the most abundant in the g ill _r&hcgsrler ,,., net catch, was second at 15.117.. Ophîcephalus striatus,Oxyleotris mamoratus 'i'' '::- and Ophícephalus micropel tes ranked third, fourth and f ¡f th at l0 ,45%, 7.90'Á 'i- and 7.20% respectively (faUles 69 and 61). There was a marked difference between the species composition of fish caught by the gill net and by the electro fishing. G¡ I I netting. appeared to work more effectively upon the depressed form fish, while electro fishing was better for the compressed or streaml ined forms with larger body size. , The mean biomass of fish caught per.gill net set ranged from 10.50 g '|02.50 to 210.50 g. The total catch increased from g in January to 210.50 g in March and decreased to 30.75 g in April. The decrease was because of the ;,,: poor water quality caused by the ,d""o*position of grasses. The catch ', was minimum in October 1975 (t0.50 S), which was the initial stage of the ',1.:, second year re-establishment of the grass covered habitat.The catch then increased ¡ November and December wlren the whole area was completely under high water. The total biomass caught during the l0 month period was estimated to be \.39 kg, ,i.l and the average weight for each fish caught was 61.78 S. 'Anabas testudineus, 0sÞhronemus gonamy, Trichogaster pectoral ¡s and Torichogaster t.¡clrgpt*_:- F. Anabantidae r^rere caught very frequently during theperiodNovember1974toApril1975,whenthewaterlevelintheGrassArea 107 was relativeìy shallow and the established grasses were still risÎng above the water leve'l . l,lotopterus notopterus F. Notopteridae, Luciosoma UlSg!Ç..!- Steinachner, CJc_loghei I ichthys e_lgpþs, Puntius gonionotus, Puntius, orphoides and ArUlVrfrVn.h¡"f,tfryr truncatus F. Cyprinidae were found during the high water period- The Anabas spp.appeared to favour the shallow water associated with the semi-aquatic emergent plants, while the larger size Cyprinidae chose deeper water under vegetation. 6.2 F¡sh fåuna in the l,Jeed Area From gill nett¡ngrlB species of fish were caught in the l^leed Area, paralaubuca sp. was most abundant (Z\.OO%), Luciosoma bleekeri second (14.00%) and pristolepîs fasciatus third (.|0.002). 0steochi lus hassel ti i and Notopterus notopterus tied for fourth at 8.00%. '¡t:"' ì Electro fishing again collected more species of fish than gill netting' ' ..- .L^ greatest. , nmong the 26 specîes caught, 0phicephaìus lucius made-^l^ up the amount , 17 .60'¿, Tr ichogaster pectoral is accounted for 15.282, 0phicePhalus str iatus g.gO%, and, both 0steoch ¡ I us hassel t i i and p¡y-leglrts mamoratus 9.657.. The mean biomass of f ish caught per gi ll net set within the l'/eed Area was second among the three areas,33.44 g/set. The catch ranged from 0 to the maximum of 165.60 g in February. The average of 14 months catch per . ,"i(data from May - September included) was 32.25, which is slightly lower than the l0 months average. The total catch appeared quite stable after the '" vegetation mats drifted away during the storm in September. The total biomass caught during the l0 month. period was 1.36 kg and the average weight for each fish caught was 27.14 S. 108 :j: : I 6.3 Fish fauná in the open Water Area tr**er@aught in the area by gill netting, Paralaubuca sp. was the most f requent at 37.037.. Anabas lg_Ltfjjlggs was second at l4.BlZ, and Cirrhinus n-l_qIgl_qús th¡rd at 9.257.. @s ..-..: .,,.,,,, enoplos and PISI_olsp_!_s fg5çjglts ranked fourth and fifth w¡th 7.40% and 5.55% ,.,,. respectively. There were no data from electro fishing because it was in- effective when appl ied in the open-water region. ,i. ,t The total biomass of f ish caught per gil I net set was 25 .63 g for the ',. :.''1...:, :,.., : _,.-::.: ..t.)t: :: lowest for the three areas. The total biomass caught during the I0 month " '' r period was estimated at 1.03 kg and the average weight for each fish caught was 18.99 s. 6.4 Thè relative åbundance of fish among the three areas 6.4.1 Time The analysis of variance shows a signif icant difference (p ( 0.01) arnong the three areas over the period of l0 months and also between the l,Jeed Area and the Open VJater Area (p(0.01) over the entire 14 months (faUles 62 and tr:). The '::', '.::.: biomass of fish caught within the Grass Area appeared to vary less 1,,,;,''. than in the Weed Area and the O'pen |Jater Area during the period November lg74 - ,,"."' '''. April 1975. The catch of fish from all thnee appeared to increase during the high flood period. 6.4.2 Area :_. -_- ._ i_....,, The analysis of variance (faUles l-2) showed that the catch of fish in the Grass Area u,as signif icantly higher (p (0.01) than in the Weed Area and Open hlater Area.. The catch of f i sh in the Grass Area was 109.69 g/set, compared w¡th 33.9\ S/set and 25.63 g/set for the lleed Area.and the gpen Water Area 1_09 respectiveìy. The average catch in the t/eed Area and the 0pen Water Area over the entire 14 months was 32.25 g/set and 26.15 g/set, respectively. 6.4.3 Time x Area There was an interaction (pa0.05) between time and area in the analysis for the l,/eed Area and the Open Water Area over the period of 14 months ,i,, .,t.t, (fa¡le 63). The highest catch of f ish in rhe l/eed Area in February (165.50g) and thezerocatch data from the Open l,Jater Area in November, April, May and September appeared to be the main contribution to the interaction. There was no interaction between time and area ín the analysis among the " Grass Area, the Weed Area and the Open l^/ater Area. ,' , 6.4.\ Mesh r The analysis of variance shows no sígnificant difference in catch f among the three mesh sizes (3,5 and 8 cm) for the three areas analyzed over ì ,he l0 months period and between the Weed Area and the Open Water Area over I the 14 months period. The average biomass caught per êrea by the 3 cm mesh size was 19.73 S i (35.28 g fromArea B, 14.23 gfromArea C and 8.00g fromArea D) . The 5 cm mesh size caught 21.64 g (44.63 g from Area B, 8.68 g from Area C and 11.63 I S r from Area D). The B cm mesh size caught 15.41 g (29.78 S from Area B, 10.53 g : from Area C and 6.00 g from Area o). (fanle 59). 6.4 .5 T ime x Hesh There was a significant (p (O.Ol) interaction between time and mesh for the analysis of three areas period (fanle over the of l0 months 62). The ,t catch by the J cm mesh size appeared to vary more in the Grass Area and was highest in November 1975 (169.5 g). The carch in the 5 cm mesh size also fluctuated over time, perhaps even more tþan for the 3 cm mesh size. The very evident peak in February is related to the moderately high oxygen content ,,:. -::r' under the vegetation mats. The number B cm mesh size apparently could catch 110 the f ish only during the period llover.rber 197\ - Apri l 1975, indicating the inshore migration of larger f ish, r.vhich probably'were ,attracted by the abundance of food in the I ittoral area during ah" f lood . -",, _, . There was no interaction betv,¡een area x mesh or time x area x mesh in ei ther test. '1.ì: I TABLE Thc mean welght 58. oi r¡rn caught by a set of experlmental-- 'r: ' glll nets. H (^ ARTA NOV DIC FEB IJ SEP orc qto *.) (14 m. ) r8r.00 t\3,75 ¡02.50 179,25 2lô.50 30.75 26,00 t0.50 l07.oo t05.5o 109.69 1r0.00 lr2.0o 19.25 0 165.50 4.00 8.75 15,00 It|.oo \l ,25 23.00 28.7' 26,50 23,50 33.9q 32,25 ñ o 56.25 5o.oo 55.5'O t8.75 0 o 6\,75 39.50 5.50 0 7.50 \6,50 2t,35 26,9 26.15 Hean 66,1tr 66,67 6\.17 133.42 77 ,7\ 13. | 6 7,50 29.38 40.7S 23.38 t6.32 15.58 60.00 49.59 ts H H ' ,; ', a ]-L2 TABLE 59 The mean welght of fish caught by a set of experimental glll nets by each mesh size amongthe Grass Area (B), the Weed A.rea (C) and the Open Water Area (o). AREA MESH slZE (cm) ¡ (e) '(10 (1-0 n. ) (14 m. ) rn. ) (1-4 m. ) (10 ur. ) (1a m. ) B 35.28 c 14.l\ 15.68 8.68' 9.05 10.53 l.Sz D B.oo 8.6r I1.63 ß.zs 6.oo 4.zg .|5.4.| Hean 19.33 t2.t4 21 .64 il.t5 5.gO -tt i,líi:,;-",;.' LL3 TABLE60. The total number and species of fish caught by "orporition -and Electro Fishing (15 m¡nute run) from the Grass Area (B) rhe lleed Area (C). GRASS AREA VEED AREA .. ..(B). . (c) NUHBER SPECI ES NUHBER SPEC I ES .CAUGHT .COHPOSITI OH CAUGHT COHPOStTt ON Notopteru$ notopterqs t5 3.48 t7 4.55 Hastocernbel us armatus I o.23 0 'o Paralaubuca sp. 2 0.46 0 0. Luciososp bleekeri I O;2J 3 0.80 Hampa la rnacrolep i dota 2 q.46 3 0.80 H. dlspa 6 ¡.39 7 t.87 Cyclochei I Íchthys enoplos 5 t. ¡6 5 |'3q Cirrhinus microlepis I 0.23 I 2.t4 Puntius gonionotus l0 2.32 t5 \.02 P. orphoides ¡6 3-72 I 2. t4 Osteochilus hasseltii 3o 6.97 36 9.65 Labiobarbus kuhl í i 7 t.62 2 . 0.52 Horul . ius chrysophekadion tl 2.55 2 0.52 Val lagonía attu I o.23 2 0.52 ûnpox birnaculatus 4 0.93 T 0.26 'apogorì Kryptopte rus 7 l -62 I 0.26 K. bleekerí 0 0 I 0.26 llystus nernurus 2 0.46 ¡ 0.26 l{. vi ttatus 6 t.39 ll | .07 Xenentodon cancf loides 6 ¡.39 2 0,52 Osphronernus goramy 5' t.r6 9 2.41 Trìchogaster pecto¡al is 65 l5,l l 57 15,28 'T. trichopterus .6 I i39 t3 3.48 Ophicephalus lucîus 85 t9.76 66 r7.69 0. striatus \5 | 0.46 37 9.8 | 0. micropeltes 3l 7.20 35 9.38 Pristolepis fasciatus 26 6.04 r4 3.75 Oxyleotris mamoratus 34 7.90 36 9.65 4¡o I 00.00 373 I 00. 00 t:ri 114 fRgLe 61. The total number and species comPosition.of fish caught by the experimental G¡ll tets frorn the Grass Area (B), the lleed Area (C) and.the 0pen l'later erea (D) eR¡ss anen WEED AREA OPEN VATER AqEA . (B) (c) (D) NUHBER SPECIES NUMEER SPECIES NUHBER SPECIES CAUGHT COHP. CAUGHT COHP. CAUGHT CO}'P.. Notopterus notopterus 2 2.8r 4 8.00 | I .85 Paralaubuca sp. 2 2.81 l2 24.00 20 37.o3 Lusiosorna bleekeri 4 7.54 7 t4.00 | t.85 Cyclochei I ichthys enoplos 3 4.22 I 2.AO 4 7.40 Cirrhinus microlepis I t.40 0 05 9.25 Puntius gonionotus I t.40 0 00 0 P. orphoides 0 0 0 o2 3.70 P. I iacantus I | .40 I 2.00 0 0 0 Punt iopl i tes proctozysron I | .40 I 2.OO ,0 Osteoch í I us l¡assel tii 0 0 4 8.00 | l .85 0. schlegel i 0 0 2 4.00 0 0 Labiobarbus kuhl i i 0 0 I 2.00 | 1.25 Arnbl yrhynchicthys trunca tus 4 7.5\ 3 6.00 I | 4.8r l{orul i us chrysophekadion I r .40 0 00 0 Neacanthopsi s gi'aci lenti s 0 0 3 6.00 ¡ ¡ .85 Ompox binnculatus 0 0 3 6.00 I | .85 KryptoPterus aPogon 0 0 I 2.00 2 3 -70 lfystus nemu.rus 4 I | .40 0 00 0 t{. v ¡.ttatus 0 0 I 2.00 0 0 Anabas testudineus tl | 5.49 0 02 3.70 Trlch.ogaster pectoral i s t7 23.94 I 2.00 | | .85 T. tr¡choPterus l3 ¡ 8.30 I z,QO I t.85 T. macrolepis I l ,4o I 2..00 0 0 Ophîcephalus lucius 3 \.zz' 0 00 d 0. striatus I t.40 0 00 0 0. micropeltes I r.40 0 00 0 Pri stolepi s fascíatus 3 \.22 5 ¡0.00 3 5.55 7l | 00.00 50 t00.00 5\ | 00. o0 .-__,"_,..,i1::i::: LLJ11< Table 62. The analysis of variance for the físh caught by gilì nets composed of three different mesh sizes (3 cm, 5 cm and I cm) for the Grass Area (g), the Weed Area (C) and the Open Water (D), Area excluding the dry months May-Augus t 1975. ..:: Sou rce DF Sum of Squares Mean Square F:Va I ue :k T ime 9 \7405.914 5267.323 2.046 *:l Area 2 '57206.ø22 29603.otl l¡.1lr Time x Area r8 \6157 .478 2564.3043 0. 996 Mesh 2 2363.272 I l8l .636 0. 459 ;k Time x Mesh IB 85781 .728 47 65.651 r.85r Area x Mesh \ 3565.278 89t .31 9 0.346 Time x Area 36 104007.556 2889. 098 | .122 x Mesh Res idual 89 2291 09.917 2571+.268 ,. |: 1l-6 Tabl e 63 The analysis of variance for the fish caught by gill nets composed of three different mesh sizes (3 cm, 5 cm and B cm) for the l,leed Area (C) and the 0pen l./ater Area (D) over the period of l4 months, including the dry mongth May-August 1975. Sou rce Sum of Squares Mean Square F-Va I ue T ime t3 25205.060 r 938 .850 3.395 Area I 348.107 34B.to7 0. 609 Time x Area 13 13983.393 | 07 5 .645 1.883 Mes h 2 2519.839 1259.919 2.206 Time x Mesh 26 19732.24t+ 758.932 1.329 Area x Mesh 2 1837.625 9r B.Br 2 r.609 Time x Area 26 15799.125 607.658 r .064 x Mesh Res i dua I 47967.500 571 .o4l 7. Fish Stomach Contents .The study of food habits of fish species is ne,ce,ssaly to a reservoir f ishery management prograrn, as it describes tlre quantitative ar¡d qualitative connection between'fish and their food organisms. Food habits usually refer to the food eaten, as estimated from the relative composition of food items in the stomach. Feeding habits refer to the manner in which food is captured and consumed, and how food habits vary with respect-to time of day, season, or Size and species of the consumer. Feeding habits vary greatly among species, and êmong individuals and populations of the same species. Abundance, avai labi I ity, distribution, behaviour of the consumer, competition from other fish species and abiotic conditions affect feeding. Gerking (1962) suggested that each population has its orvn habits which are related to foód preference and the relative abundance of different food organisms¡ lvlevr (lgOt ) found that different fish species preferred certain food species, and select prey within definite size limits or prey which move at particular speeds, N¡kolsky (lge¡) stated that seasonal variatïon in food eaten is primari ly caused by differences in the composition, .abundance, and availability of food organisms, and is modified by the adaptation of fish to abiotic factors. Kamol.ratana (lgZl) and Sunkagul (1973) studied the food habits of some important fish species in several Northeast reservoirs in Thai land. Pholprasi th (1974) studied the biology and some management 118 prob¡ems of thirteen economically important fish species in Ubol Ratana Reservoir, Thailand. M¡zuno and .Mori (1970) and Potipitak (lgZO) investigated the food habits of some important fish in Bung Boraped. The electro fishing device was employed in this study. Data concerning the food habits and feeding habits are presented as a percentage of each food category in the stomach content of each fish species. The degree of gut fullness is also given, as a percentage,.in the feeding periodicity study. Data on the food habits are presented in Tables 64 and65 The diagrams comparing the composition of the major stomach food contents between the Grass Area and the l,Jeed Area are presented in Figure 12. Data on the feeding habits are presented in Tables 66 and Data concerning the feeding periodicity are presented in Tabìes 68 and 69. A diagram showing the diel feeding of fish is presented in Figure ì,¡.. Cyclochei I ichthys enoplos Fami ly Cyprinidae. Mizuno and Mor¡ (1970) reported that this fish fed on chironomids. However Potipitak (1970) and Sunkagul (1971) reported that in Bung Boraped the major food content of C. enopìos was mol luscs and pl.ants. For fish caught in the Grass Area, plankton and organic detritus contributed most to the stomach content (79.232\. Crustaceans contributed l\.\67.. ln the V/eed Area gastropods contributed 34.79% and plankton- organic detritus -contributed 31 .96'/". The b ivalves contr ibuted 3.362 (faUles -64 anC 65). The greater avai labi I ity and abundance of mol luscs in the l^Ieed Area cculd be a factor. 0steochilus hasseltii Fami ly Cyprinidae. Mizuno and Mor¡ (1970), Potipituk (.|970) and Sunkagul (1973) reported that 0. hasselti i fed on aquatic plants and phytoplankton. LLg Jaiyen (1971) reported that Hydrilla verticel lata was the basic food of fish in Bung Kang Lava, Khonkaen.. Chookajon (1970) found that young O. hasselti i fed mainly on blue-green aìgae, green algae, desmi ds and diatoms in Ubol Ratana Reservoir. lankton and organic detritus were the principal foods. In the Grass Area plankton and organic detritus contributed 57.18'4 of the stomach contents. Plant fragments were also foundrat fi.l0Z. ln the UJeed Area plankton and organic detritus contributed 46.g0"Á and pl"nt, contributed 36.362 of the stomach contents (fa¡les 64and 6d. ln the Grass Area the contribution by plankton and organic detritus ranged f ron 37.05'Á in November to 81 .957, in December 1975. In the l,/eed Area values ranged f ron 3,63% in December 1975 to 95.00'Á in November 1975. ln the Grass Area the percent contribution by plants ranged from 3.122 in November 1974 to 100% in December 1975. In the Weed Area the plant contribution ranged from 5.007. in November 1974 to 96.31% in December 1975 (Tables 66 and 6T-). 0. hasselti i is a diurnal feeder, paFticularly during the evening. The fish was very active from 1600 hours to 2000 hours. The percent gut fullness ranged from a minimum of 2.2\% at 400 hours to the maximum 97.01% at 2000 hours (fante 63). Plankton and organic detritus were found in stomachs of fish between 800 and 2000 hours, but not at 400 and 2400 hours. The contribution of plankton and organic detritus ranged f rom I \.7t+% at 1200 hours to 45 .91% at 2000 hours. Plants 'always occurred in the stomachs. They ranged from 0.56% at 1200 hours to 37.29% at 2000 hours (faUles 6E and 69). ):.:1.. L20 MoLul ius chrySophekodion Fami ly Cyprinidae. Pholpras i t (197\) cons idered th¡s f ish to be herbivorous. Veerakawoot and Jaiyen (1970) 85'¿ l0% debris and 5% found ^lgae, protozoansand crustaceans in the stomach contents of M. chrysophekadion collected from Ubol Ratana Reservoir. Mizuno and Mor¡ (1970) and :) Potipituk (1970) reported that fish from Bung Boraped fed on debris. This fish is found to be a plankton feeder. In the Grass Area organic detritus contributed 79.0g% of the total diet and in the lJeed Area 67.752. Plant f râgments such as f ilamentous algae also occurred, contributing ll.5OZ in the Grass Area and in the Weed Area 32;24% (Tables 64 and 65). Trichogaster pectoral is Fami ly Anabant idae. This fish is found to be a plankton feeder. Plankton and organic detritus contributed 7l.Bl% to the total contents in the Grass Area and contributed 58.187" in ¿he l,/eed Area. PIants, insects, : crustaceans and mol luscs are also present (tables 64 and 65 ). In the Grass Area the amount of plankton and organic detritus ranged from 6.69% when the storm was severe in 0ctober to 100% in the calm and hot month of May. In the Weed Area the percent contribution by plankton and organic detritus fIuctuated Iess than in the Grass Area, ranging from 27.63% in January to 100.00% in May and June. ln the Grass Area the plant contribution ranged from 0 in April and May to 55.05"/" in November, compared with the l^/eed Area where the range was 0 in May and June to 53.12'/" in 0ctober (tables 66 and 67 ). This fish is considered nocturnal. lt is active from 2000 hours to 400 hours. The percent gut fullness ranged fron 2.25% at 800 L27 hours to 100% at 2000 hours. Crustacea were found only at 400 hours and 1600 hours. Plankton and organic. detritus were found in the greatest quantity (75.16"/") at 2400 hours (tables 68 and 69 ) . Tlichogaster trichopterus Family Anabantidae. This fish is considered a plankton feeder. In the Grass Area the plankton and organic detritus contributed 61.107 to the stomach content. crustaceans and insects occurred at 3'10% and l'83% respectively' ' t n the Weed Area the pl ankton and organ ic detr i tus compr i sed 58.91'¿ of the total food contents. Insects occurred at 12'57% and crustaceans at 0.06l¿ (taUles 64 and 65). The considerably higher density of insects in t the Grass Area may be the factor respons ible for the relatively larEer contribution of insects in stomachs of T. trichopterus caught in the Grass Area compared to the l^/eed Area. l. trichopterus is considered nocturnal. lt is active from 1600 hours to 800 hours. The degree of gut fullness ranged from 0 at the noon hour to B\.17% at 400 hours. The percent contribution of crustaceans ranged from 0 at 1200 hours to 66.48% at 400 hours. The percent cotìtribution of plankton and organic detritus ranged from 0 at l2O0 and 2000 hours to 34.18% at l600 hours (raUles 68 and 69). Puntius gonionotus Fami ly Cyprinidae. pholprasitlr 0971+) described this f ish as herbivorous. Mizuno and Mor¡ (1970) and Potipituk (1970) reported that P. gonionotus fed on aquatic plants and organic detritus. Tanchalanukit (1970) reported that young and adult fish fed on higher aquatic plants such as Chlorophyceae' Characeae, Ceratophyl laceae, Bolygonaceae and Najadaceae. P. gonîonotus is herbivorous. In the Grass Area they fed L22 mainly on pla¡rts and organic detritus which const¡tuted Bl.l6% and 17.25'Á resPectively. In contrast, in the !/eed Area plants constítuted a smaller portion than the plankton and organic detritus. The plants made up 39.38% and the plankton and organic detrirus made up 60.61%. This difference might suggest that P. gonionotus altered their food habit and uti I ized the establ ished grasses for consumpt¡on (Tables 64 and øs ). !. gonionotus is considered to be diurnal. lt is active from 800 hours to 2000 hours. The degree of gut fulìness ranged from 0.312 at 400 hours to 100.0% at 800 hours and 1600 hours (fa¡les 68 and 69). Puntius orphoides Fami ly Cyprinidae. This fish is herbivorous. Plants const¡tuted the main part of the stomach contents. They contributed 72.482 in the Grass Area and79.83%¡n the l/eed Area. P I ankton and organ ic detr i tus cont r i bu ted B .62y. in ' the Grass Area and 20.16'Á tn an" l,leed Area (Tables 6¿ and OS ). P. orphoides was active during the sunset ( 1600 hours to 2000 hours. ). rrre degree of gut ful lness ranged f rom 2.2\% at 400 hours to 97.01% at 2000 hours. The composition of plants in the stomach contents ranged f rom 1.6\'¿ at 1600 hours to 50.87'¿ at 2O0O hours. The contribution of plankton and organic detritus in the stomach was highest(55.027")'at 2\OO hours (Tables 68 and 69). Labiobarbus kuhì i i Fami ly Cyprinidae. This fish is herbivorous. Plants, plankton and organic : detritus are the staple foods. In the Grass Area plants contributed 73.502 to the stomach contents. Plankton and organic detritus contributed 26.\9"/.. However in the l^leed Area the stomachs contained 94,72% of plankton and organic detritus and 5.277, of plants (Tables 64 and65 ). (..,-:::' L23 The greater contribution of plants, such as grasses, to the stomach contents of L. kuhlii within the Grass Area may indicate the importance of grass as food. Osphronemus goramy Fami ìy Anabant idae. Sunkagul (1973) reported that this fish fed on aquatic insects and plants in many Northeast reservoirs in Thailand. Tanchaìanukit (tgZO) reported that 0. goramy fed on aquatic plants. The fish is considered herbivorous. In the Grass Area and in the Weed Area plants contributed 82.50% and !!.142, respectiveìy, to the stomach contents. 0l igochaeta also occurred in stomachs of fish f rom the lJeed Area , at 4.277o (faUt es 64 and O5 ). Notopterus notopterus Fami ly Notopteridae. : Pholprasith (lglt+) described this fish as carnivorous. Potipituk (lgZO) reported that in Bung Boraped the fish fed mainly on aquatic insects. Kamolratana (1971) reported insect larvae made up 60% of the diet in Bung Kang Lava, Khonkaen Province. Jensinisak (lgll) reported that insect larvae (Macronica sp.) were the basic food in ;i"',: Ubol Ratana Reservoir. Freshwater shrimp (0. mysidacea) were the 'r" .-.... secondary food, while a small amount of plant detritus was also found. ,.;. N. notopterus is considered insectivorous. lnsects contributed 66.412 and 64.11;% to the stomach contents in the Grass Area and the Weed Area, respectively. Crustaceans, pêrticularly freshwater shrimps, 0l igochaeta and plants were also frequent. Crustaceans contributed g,51"4 in the Grass Area and 7.g\'Á in the V/eed Area (faUles 64and 65). In the Grass Area the amount of insects in the fish stomach contents ranged from 0 in February to 1009l in September. The Crustaceansl l,''¡i'i L24 contríbution ranged from 0 ¡n September to \5.27% in November. ln the lnleed Area the contribution of insects to the stomach contents was quite stable compared to the Grass Area. lt ranged fron 65.20% in May to 100% in June. The crustaceansr contr i but ion ranged f rom 0 in June to ,'',.,,, 22.16% in November (Tables 66 and 67 ). [. notopterus îs considered nocturnal. lt was active during the period 2000 hours to 400 hours. The degree of gut fullness ranged from 36.00% at 1600 hours to 99.93'Á at 2400 hours. The contribution of insects to the stomach contents ranged from 0 at 800 hours to 65.81% at 2000 hours. The contribution of crustaceans ranged from B.Bl% at 24OO hours to 29.47% at 400 hours (tables 68 and 69,) . Ompox bimaculatus Fami ly Si luridae. Mizuno and Mor¡ (1970) reported that 0. bimaculatus in the River Kwaí, Kan chanaburi Province, fed on smal I shrimps. Pholprasith (1974) reported that in Ubol Ratana Reservoir they fed maínly on freshwater shrimps and smal I fish. The fish is considered to be an insect and crustacean feeder. In the Grass Area insects and crustaceans contributed an equal amount to the stomach contents,49.gg7.. In the l^leed Area the fish contained 79.5\'/, crustaceans and 1g.64% insects. Kryptopterus apogon Fami ly Si luridae This f ish is an insect and crustacean feeder. ln the Grass ,,,r, . -:ì._:: Area the fish contained insects at 68.977. of the stomach contents Crustaceans contributed 27.g\%. ln contrast, within the l,/eed Area the fi sh stomachs contai ned 6 | .50% crustaceans. I nsects were second in importance, contributing 38.50%. The higher percent of crustaceans in L25 stomachs of fish within the l,/eed Area indicated the abundance of freshlvater shrimps which were observed to be associated with the stand of Eichornia class i pes . Mystus vi3tatus Family Bagridae ,,..,.., Mizuno and Mor¡ (1970) reported that in Kwan payoa, Chiang Rai Province, Thailand, th¡s fish fed largely on aquatic insects and f reshwa ter shr imps. Pot ipi tuk ( 1970) reported that the f ish f ed on 1. ,,, phytopl ankton and insects in Bung Boraped ,'- ,t,, , ,,- M. vittatus is considered insectivorous. In the Grass Area the ,',',,1' f ish contained 83.11% insects, 9.66'Á plankton and organic detritus, and smalI amounts of crustaceans and aquatic plants. In the t/eed Area plankton and organic detritus comprised the larger part, 68.llZ. lnsects and crustaceans contributed 25.00% and 2 .36% respect ively (faUl es 64 and65). Pristolepis fasciatus Family Lobot idae. Pholprasith (1974) described this fish as insecrivorous. Sunkagul et al. (1972) reported that in Rum Dom Noi Reservoir, ubol Rajathani Province, the fish fed 70% on aquatic insects. Benjakan (1g73) reported that P. fasciatus in Ubol Ratana Reservoir fed 80-B5Z on aquatic insects. However, Potipituk (1970) stated that p.fasciatus, in Bung Boraped fed 90% on freshwater clams. P. fasciatus is considered an insect and crustacean feeder. ln the Grass Area the fish contained 2!.33% insects and 28.61% crustaceans. Gastropods comprised 1.23% of the gut contents. ln the Weed Area insects and crustaceans contributed 32.19% and 30.157o respectively (faUles 64 and 65 ). L26 The contribution of insects ranged from 0 in August to 100% in June within the Grass Area and ranged from 0 in May to 90.007" ¡n February within the l,/eed Area. The crustacean composition in the stomach of fish ranged from l.86Z in November to 89.002 in March in the Grass Area, and f rom 0 to 77.73% in the l^/eed Area over the same period of time (Tables 66 and 67). There were two major active periods for P. fasc¡atus. The first was during the period 400-800 hours when the gut fullness ranged from 91.72to95.36% respectively. The second was during the period 2000-2400 hours, when the gut ful lness ranged from 9l.43to 100%, respectively. Ths contribution of insects was highest (16.53%) at 400 hours and lowest (2.2\'Á) at 2400 hours. The contríbution of crustaceans was highest (16.84"4) at 800 hours and lowesr (0.412) ar I2o0 hours. There was no i sample ar 2000 hours (tables 68 and 69 ). Oxyleotris marmoratus ¡ Fami ly Eleotrídae. : potipituk (1970) reported that this fish in Bung Boraped was carnivorous as the whole of its stomach contents consisted of freshwater ,: ,' shrimps and fish. Benjakarn (lgll) reported that 0. mamoratus in Uboì Ratana Reservoir fed 50'Á on freshwater shrimps, 28% on insects and l\% on fish. A small amount of aquatic plants were also found. The fish is considered an insect and crustacean feeder. ln -, the Grass Area the fish contained 52.\\7" crustaceans,9.63% insects, .: and 4.152 small fish. In the Weed Area the fish contained 64.05% crustaceans, B.g0Z insects, and 2.122 fish. 0ther organisms such as 0ligochaeta, plankton and pìant fragments were also found in stomachs of fish from both areas, but in relatively small quantities (faftes 64 and 65 ). L27 The contribution of insects to the stomach contents ranged from 0 in Harch to 80.002 in January for the Grass Area, and from 0 in November 1974 and 1975 to 50.00? in January for the Weed Area. The contribution ,.., of crustaceans ranged f rom l8.6lZ in November 1974 to 100% ¡n June for the Grass Area, and ranged f rom 25.00% i n Ju ly to 85 .35'Á i n November 197\ and 1975 for the l/eed Area (faOles 66 and 67). .,., 0. mamolatus appeared to be a continuous feeder. lt was active .', at 1200 hours to 100% at 800 hours. The contributíon of fish to the stomach contents was highest (97.63%) at 800 hours and lowest (4.82%) at 2000 hours. The contribution of crustaceans ranged from 0 at 1200 hours , to 49. 99% at I 600 hou rs (rau I es . 68 and 69) . ; Hampala macrolepidota Fami ly Cyprinidae. tttr* t*t reported that this fish in Kwan Payoa "* ,*/0) , Reservoir, Chiang Rai Province, fed mainly on young fish. Potipituk ' (1970) reported that H. macrolepidota fed largely on zooplankton and :, crustaceans in Bung Boraped. -.,l This fish was found to be carnivorous. The stomach contents ,:. l,l of f ish caught f rom the Grass Area nere 60.64"¿ plankton and organic detritus, 2i.00% crustaceans and 2.36% plankton-feeding fish such as Trichogaster sp. The fish in the h/eed Area contained 44.21% crustacean, ,r-*"r*'r* .nd 8.16% insects (tables 64 and65 The large amount of ,,'. ). plankton and organic detritus in the stomachs of H. macrolepidota caught from the Grass Area might be caused by food eaten by Trichogaster sp., uch as plankton and organic detritus which are very d¡fficult to digest. They might remain and accumulate in the stomach of H. macrolepidota ¡ ::-t-: _l 1tQ .:.::-l:.1::-::.: t,_,; ,i:.: :._.: :.- ''-'-'.,'-.: ì.:-ì_.: which is considered a continuous feeder. H. macrolepidota was most active during the dayl ight hours. The degree of gut fullness ranged from 9.99'ó at 2400 hours to 100% at 1600 hours. The most ¡ntensive feeding time appeared to be between ..,,..,-.....1,.., 1200 to 2000 hours, as the degree of gut fullness was 99.35%, 1007. and /1.39% at 1200, l600 and 2000 hours, respectively (t"blus 68and69). Hampala dispa Family Cyprinidae ,..:....:.::,: Pholprasith (lglt+) stated that this f ish was a predator in Ubol ";";' '"'"'¡; .',.:'-.:.: -..a t :.! -': Ratana Reservoir. Benjakarn (1970) reported that the stomach contents of '::::,:'.'.':: fish collected from the Ubol Ratana Reservoir were B0% small fish, lO% freshwater shrinps, T% insects, and the remainder nematodes and crustaceans Koanantakul (1972) reported that freshwater shrimps were the staple food of older fish while insects and small fish were second and third in i mpor tance. H. dispa is considered carnivorous. In the Grass Area the fish contained 53.08% crustaceans, (mostly f reshwater shrimps), lZ.9O"/.'plankton and organic detritus, and 7.56'Á f ish. tn the l./eed Area the stomach :;:,:i,.::..:..... ì1';;'';i:'i":'';' contents were 61.127. plankton and organic detritus and 38.782 small i (tab I 65) f sh es 64 and . -.: _.- ,'.":;'':;'l':;"""".;"' : . : Ophicephalus lucius Family 0phicephal idae Sunkagul et al. (lglZ) reported that this fish in Lam Dom No¡ Reservoir was carnivorous. Pholprasith (197\) reported that in Ubol ,,,,,,;.,., 'ì'r:1 :.' Ratana Reservoir smaì I f ish const¡tuted 93-gg% of the total stomach con tents This fish v¡as found to be."rn¡uororr. ln the Grass Area the f ish contained \5'06% smal I f ish and l\'47% crustaceans ' The stomach .'r:'":'i.'l''r' 'ìì,t,i L29 contents of físh collected from the Weed Area consisted of 35.722 small fish and 2\.60% crustaceans. Insects, 9âstropods, plankton and organic detritus were also found in both areas in small quantities (Tables 64 and 65). The fluctuations in the percent contribution of fish to the stornach contents were similar in both the Grass Area and the !/eed Area. ft ranged fron \.82% in June to 97.087. in October in the Grass Area, and from 8.\2'¿ in April to IOOZ in October in the l,/eed Area. The contribution of crustaceans to the stomach contents ranged from 0 in September to 76.38'Á in June within the Grass Area, and ranged from 0 in October to 60.98% in April within the Weed Area (faUles 66 and67 ). 9-. lucius appeared to be a continuous feeder. The degree of gut fullnes: ranged from 58.68% at 1200 hours to 99.09% at 2000 hours. The contrïbution of fish to the stomach contents was a maximum of 48.71% at B0O hours,sand a minimum of 11.527. at 2400 hours. The contribution of crustaceans was highes t (24.73'ò at 2000 hours and lowest (0) at 4OO and 300 hours (fables 68 and 69). 0phicephalus striatus Fami ly Ophicephal idae. Tranchalanukit (1970) reported that this fish alters its food and feeding habits with age. Fryfeedmainly on plankton and crustaceans, and juveni le and young on crustaceans. The adult is truly carnivorous. Kamolratana (lgll) reported that the food composition of 0. striatus in Huey Taey Tank was 55% small fish, and 24% annelids. 0. striatus was found to be carnivorous. Fish in the Grass Area conta i ned 45.74'Á f i sh, 7 .352 crustaceans and 6.997, i nsects . The stomach contents of f ish in the Ì.leed Area were 32.99% fish, 17.22% insects and I .77'/, crustaceans (tables S4 and 65). 130 The contribution of fish to the stomach contents of 0. striatus in the Grass Area ranged from 0 in December 1974 to 100% in April, compared with O in June and July and 98.85"Á in December 1975 for the lJeed Area. The contr ibut ion of insects and crustaceans was. f ound to ' ì:I--:-,:..."',.,,' vary greatly over time in both areas (fa¡le 66 ancl 67). The fish appeared to be a continuous feeder, active throughout the day. The degree of gut ful lness ranged f rom I 5.85% at l600 hours ,,:.,,,i. ..' rii:ì to 78.87% at 4OO hours. The contribution of f ish to the stomach contents '-:,:r',. : ..: ',;,'.'l',".: v,,as greatest at BO0 hours (75.002) and lowest at 1600 hours (6.69%) (Tables 6g and 69). 0phicephalus micropel tes Fami ly 0phicephal idae. Smith (1945) and Sithimunka (1972) noted that the fish was carn ivorous. Phol pras i th (lgl4) reported that sma I I f i sh made up 67% of the diet of 0. micropeltes in Ubol Ratana Reservoir. 0. micropeltes was fosnd to be a predator. lt consumed prey of all kinds and sizes. In August 1975 one specimen contained 200-300 young 0. micropeltes which brere approximately 2 cm long. ln the Grass , ..,,r.,.-1., , Area the f ish contained 57.432 f ish, and 55.82% in the Weed Area. t't':',' ' ::...,.,.r,¡.. Insects and crustaceans were also found in the stomach of fish from both ;.::.:1,':;,,¡ .-r: ::.. _: : areas (rao I es 64 and 65 ) . The contribution of fish to the stomach contents of 0. micropeltes ranged from 0 in September to 100 in August and December ,,.l:l ,,,,,,,..,,,:-_ .: i: :: , 1975 in t'he Grass Area, and ranged from 20.00% in October to 100% in March, April and December 1975 in the Weed Area (fa¡les 66and 67). 0. micropeltes was found to be nocturnal. The degree of gut fullness ranged from 14.6\% at 1200 hours to 100% at 2000 hours. The ri.i: :'t:i 13L contr ibut ion of fish to the s tomach contents was highest at 800, 1600 and 2400 hours (49.99"Á) and I owes t ar 400 hours (l3.0lZ) (faUles 68 and69 \ Figure 12. The contents in stomachs of fish from Ëhe Grass Area (B) and the lleed Area (C). f:- r:,: L32 B B c 7c c tl i:iií il¡tij ffiLt i"'.. l hti',iitl Ërtiï ':;äi lÍiiiÅ í.s'ì:i [i"r,:tir;l Jí )ì^ 'yit;rì' Þ "'ìÌ;:rr Cyclocheilicfhys Osleochilus Morulius Trichogosle Trichogosler enoplos hosseltii chrysophekod ion pecf orolis lricho plerus B BC B BC Fø..*l t¡'.:'it f.;f,ï] ?::ia;..) F..T$H ffi flLia:i-l-*¡ tÄs{ ffir tl llt*T tl tttl l'Ê:.!} | fËni tt tttl| I tttl|tl tIl |ll tttltIl tttl t||l L] L__l L_l tttl Puntius Puntius Lobiobobus Osphonemus gonionotus orpho ides kuhii goromy CB CB BC CB Noloplerus Ompox Kryplopîerus Myslus Pristolepis Oxyleotois noÌoplerus bimoculof us opogon villofus fosciolus momorotus BC B BCB B c roo FF',,.fi FISH J PELECYPODA hÏ GASTROPODA INSECTA tffi CRUSTACEAN OLIGOCHAETA ORGANIC DETRITUS ffi PLANT Hompolo Hompolo 0phicepholus Ophicepholus Ophi cepholus mocrolepidolo dispo lucius slriofus m ¡cropeltes Fígure 1-3. The diel feeding as expressed in percent of fish stomach ful I ness L33 Osteochilus hosseltii Trichogosler pectorolis Trichogoster trichopterus ?400 2OOO /Á ,,rq@,,% I t--I I t I \ \ 1600 \ '-iY)"' Puntius orphoides 'Puntius gonionotus Notopterus notopterus - -.tI \-___z/ Pristolepis fosciolus Oxyleofris momorotus Hompolo mocrolepidoto ,,;@l --J I I I Ophicepholus lucius Ophicepholus striotus Ophicepholus micropeltes l-----, ':: : .:. \¡. ( (¡9r'rl {zti't8 (!85'l ls.r'. r8¿'rl -9\¿'¿ll .ttt.0) .640 0) -600'0) -¿¡ l'0) rr.¡rú¡ãrú,n,io.r,roo 6¿0'r 8fì'o 06¿'a (tf'¡ 8tl'lf (t9( (lü (tf9 ¿9 (ì06 lI ¿l 0r . -¿09'ì¡) -00('0) -0¡t't) .ìr¡'Q) 6¡.t¡¡. ¡0tqó.tltdo . (tfì 366',e Ê\¿'li (rol 09. 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St 0'0 000'g ' (996.65 (f¡t 16 (¡09 ¿6 (00'00 I (00'001 lct... (tr6'J6 .69r 'z , -f6¿.r) r¡ ll'0) -900'01 -oo'oô t) | ) l¿ 0'o . fr¿'$ - ¡tatut ñ¿Ð¡do¡ou ¡n/.¡do¡ol | | 9'5t ¿59 ¿ì 000'00 | ;ål!;') ;i;{;¡" Stt (ì6¿ r6 (06l1fg (f¿0'5t (t09'tf r<ôô¡'r (26ì'tl (5¿o'fì (8rz'r¡r (lo9'¿r' (f -tg9'9) -96t'0) -f09'¡ | ) -6fl ìrl -50e il) -rf9 9) -f09 r) ';iit;1" l6'!-o'o) ¡urtd¡lls¿oltúrСrr'ó¡lttJ¡ ¿f0 5f . mo'05 l6í'za 6rt'l ;åi?;i') 0'0 0'0 0t¿'0 f58 ¿r 0!f 8 f09'¿l (9rt (00'00r (69r'¿6 (0o ool (o¿6'96 (009'8¿ (fr6 56 (06¡ 60 (8lo'¿,r (01¿'96 (aì'ol (6otzt o! . -til -.f9 58) -9lf'95) -ol¿'r¿) -056.12) tô¡rr¡?0 -¿10 0) -¡04't) -9ot'ot) -006'f) -990'0' 'bll ì, -oo'oot) rf) àl!.ór0.il¡ro¡r¿drà¡¡.óo{tl¡t 9r6'ìt 869'9 ¿0ì't¿ ¿¿t'¡ ooo'fz tt9 ll 000'00t ì5t'6¿ 55z'66 tìr'¿¿ 16t'05 ooo.l¿ t*'oor (6¿t '!6 Itít'.s 16rz'_ftt.z) 11. -00 00t) -858 9¡) _0rr¿.2). (¿59'of'o'o) . ¡ufl¿ | ¡nl¡qto¡lto 00'æ I 0ì6 ¿t , zs6'tt il l'9 tr¡'t l¡t.lrq (056't0 (fo9'oB (rff'8¿ (oo ool (056'66 -08¡ -0ìr'fi) . rñ¡l¡¡¡0 -0f5.te) -92¿'f'l 8) 'zol'62) rñllqror¡¡o ol6'r9 6S0'¿f - (9f'0t 888'f¿ I 8t'¿¿ - alu.6¡O t¡1.¡¡3{ ¡¡0 ¡N¡¿M¡ 'tl¡ ¡.ac (¡l ..¿v tit¿o .tt -r¡ qi*ra \.1, rt ¡¡c.¡!ot pæ¡ ¿cfd.{¡ ¡c ¡ilrll .ru.pt¿É2 tf6 Pct ¡u.¡¿ú ut* "r¡ tp ¡1¡t^ i., :l:::; r\ cî F{ (l¿o'58 (09¿'94 (ror'9r _0¿6.f1 -98r'o) -ofo'o) c..2.¡¡ô/¡ t¡ll.ø/tl{ lñ¡qdatlqd0 . 000.08 981'l I r o¿ì'¿ 0'0 0'o (t¿ì'Bt {Bfl'zt -t9t'o) -o9o'o) 0'0 0'0 .06('( iro'a 0'0 0'0 0.0 ¡Ð¡!t re¡t¡do¡ttr ¡ñtrqdrtlqdo (æ'æt (¡¡r'f6 (¿16 86 (6¿É'¿8 (oo'ooi (00'0ol (m'oo I .æ.00t) -0'01 -509'fr) -00'00r) -00'00r) .¿81.¡l -s.L'.zl rñLqdr:lqdo 00'001 0@'01 tÍr'69 ì¿¡'05 000'00t 0m 00t 0@'06 {r¡J r¡l t.Cor3lr (att.Ot (lto: lf (00'o0t (0o o0l (¿ r8'6t . (016'¿t (080'zt . -0 -t95'.) -t9¿'0) t!0.0) -0.0) -00'00r1 -æ'6¡) 0). .n¡!lJ¡a ròlqc.rlldo 0'0 Þt'il 0'0 ¿0t t 00'001 æ 00| 000 J¡ 0'0 - ì8BS ¿99(r 00 rr¡4.¡tn¡¡ (90¿'09 (9t9'90 (tst's6 (t9¿ 85 -f09'il) -lr¿'o¡l -zf¿.il) -ttt'¿l) 0'0 0'0 99r'9 9¡6 ¿t 0'0 0'0 0'0 00 " F0 ' l¡0'61 Sf.'6¿ o'o ¡ã.rut ¡n¡tlr¡r tñlqd¿tlqdo (@'00¡ (99f t¿ (¿zo'92 (¿f!'s9 l.fg'el (t6r't6 (oo'0ol l\19'st (or8'rf (r¿¡'o¿ .¿ì('ll) .f09.f) -¿19'o) -8¿r'ol -l9s'tr) -sj¿'l.l -ofe'5r¡ -s60,t, -0'0) -0 01 q.¡l .n¡.,rtt .nlqó.trgdo r59 86 ¿t9 lì 09t':¿ 5l5 tf 000 05 N0 0'0 ooo'5¿ t¡¿ ì5 ' tt9 ll ú0¿'l 5rt f lts¿'tg (l to'¿¿ (s'¡ú.¿6 (o0r'96 _¿il.t) lllz'/¿ (ot¿.oE (lrf t6 (ilr'5¿ ' (lf6'28 (6¿¿'61 (6r¿'f8 -660'0) -¿69'o) -0tì'¿) .6t¿.0) -frz'91) -o'0) -trg'o) -696 t) -o'0) 98¿'5f 0'0 f98 0Í ìt9't¡ 0g¿'ot 9S6 ¿t 9tf.¿t Js6'09 869't . llo'tz tzo'¿ ¡r0 (l uÞ.¡rñr¡ rnt?ôt.ôt;td¡tt{do ( fì¿'r (tft'01 (t _0'0¡ _0.f.0¡ to'¡z (f91.¿8 (6io ?l l.t|'fz (fì¿'r -t r0'o) -6f0.5¡) ' -00) -0r -0'0) t¡6'r r r) 0'0 t66.t 0'0 | il'9 0'0 00'0 ¿¡¿ tf - ¿(f'r trl'6 166' I ¡r.¡ul rñtstútqd.tt\do ' {8f9'66 (oo'o0r (009't6 (119'66 (toe'to (69t'¿¿ (ilt'f9 (oto'ol (600'28 ' (¿60'¡8 . (¿98'9e (ìr¿ 66 -Éìc'6¡) -oo'00t1 -66(.e) -lr0 6r) -o'o) -i¿s'zl -s¿t'o) -ìu8'a) -0 01 -98¡'r) ot¿t'!l -¿o!'o) 8¡9'69 s0'00t 000.0t' tr9'69 615'6 s00'6t ¿9t't¿ 9¿t'3 lzl'0r - Éto'tr f¿0 8f (5( (f q.tl fñl¡nlrô14d.ãlqdo (fs'06 lf8¿'r6 (z5l'06 (951.9¿ (¿ (0fr'68 (r58't5 (0ft.68 -59t'9) . r9'86 (oro'¿l -tto'0) -9ìt.t) -58f.0) , f00.r r) .r¿9 8t) -t59'5f) -I¿9'il) -ì¿0'et l tf¡'59 gtl't( - gÉ('5e .ñ¡t¡oÈ.1¡¡o.l¡ro 000'fz - t0¡.f9 tÍ5'19 Jsf'5¡ 950'¿6 tc¿'6f "-r.,rnr¡ (¡lt'(9 (¡16 0s ' (0el'!9 (852 (0ú9'99 (6e6'65 -É90.0) 69 -0 0) -0'0) -0rì'01 -Ð8'!) - t0r'0) f99'0ú 0.0 ' 8¿r'S - ¡6t.9 oo'fr $9'tl 0'0 000'09 ¡ 0'0 ¡r.t!t .ñ¡.idartr¡o.t¡rO (l¿f'(f .. (loo'09 (l(f'f5 (662 f! -'¡09'0¡ i\ -Ét¡,1) r!z('01 !0.0) 0'0 990 ¿ zt8.z¿ . glt.tl 0'0 0'0 Sff r o'o ' 0'0 t¡H rnr.Jdd rl¿¡o.lÁ¡0 (5¡5 66 (55s'19 . (9ll'0¿ (f¿r'66 -l5f ¡¿¡ -0te'r) -0 jt¿'¿¿ -8t¿'zl 0) - La,'zt - &0'0¿ 000'0t - 0'0 ur.?.¡rn/t .n¡rt:¡r, ttr¡to¡3tr¿ (tf6'Í0 (oft.t6 (¿ì.'l r (26¿'ro _ lf0.f) _ffr.tl -5t¿'f) -0'0) - e9Z.tZ ' f9B'0t ¡ 0'0 0æ'06 - | f0'¿ ¡?o¡ut ¡ñ¡.t2¡.t .ld¡to¡¡tr¿ lcal'6t (¿99'¿t (o98 ot (o¿9,1f l¡t¿'st -r¿r.t) -6¿5'l) -o'o) . _0.0) -0'0) crr.¡aôrJ ' 999 44 869 9 908'f 0.0 t8t.f æ0'5 ¡ñr.¡do¡4 anl.¡&¡q (ì05'¿9 (æ'oot lali'¿6 {00'0or (ì6r'¡6 lsrs'ar .t99't) -0fl'll1 -r0r'fl) -00 00t) .100'fl .9(o'0) , 9lt'tl tot.f6 9gr'9¿ 00'mt 30t'19 æ0'f 5 ¡¡.¡91 arJr¡ø¡ouañJa¡do¡ofl (oof.9t tteì'¡¿ rao'r, (9f6'r¿ (9f¿ 68 It¿É'9ì (90f'rl torrlss rre:.¡r. t¡¡sl* torel¡, -l | 9.¿) .¿!f¿5!) .0'0) -6ga'o) -r9r'5) '-186'r) -0'0) -t89'f) -o'o) -fto'.) -€r! o) - fao lr ¿il'al ìtg'o (rt'¡¿ 0oo'02 0'0 0'0 I ro 6 f0!'0 000'0f 8¿!'f lo('ìr ¡ìo'5 ¡u!la rl trro¡r.ó r.¡rróqrtrt (o¿¿'56 (.r8'8Í (00'001 ( r¿¿'16 (oo'oor (oo'ool (oo'ool (rfï 16 loa¿'s6 (rg0'09 (19('26 (zo9 r0 (869 1¿ .9t0'¿ | ) -f(f'rl -oor'of) .066'0rl -r5r'0) -@'o0t) -00'001) -¿a6'lÉ1 -o9t'¿l) -q9¡'o) -9fÍ'l) È6H'rz) -S¿¿'6't rñ¡ ¡r¡ ¡0 e tfg 09 il8't¡ 9o¿'95 9Cf'¿¿ 000'08 00'001 00'00t 986'06 09r't9 000'0¿ 5t9.'¿¡ ¡tf zl' 16r'0t ttueórO ¡t IrJo¡i.d r.¡¡.tuirlrl (m'00r ((r6'¿9 Gtl 9t (fr9'96 l¿Í¿'¿l (¿C9'r8 (fr6'5s (J(6'¿f lssj'¿6 (lìo'06 -9er'¡ll -llf'!) -t¡z'r, -98f'() 'tt¿ rt) .tgr'il) -att'9) -0.0) -900'0r) -o'0) frl'95 om'ot. - tzf'st 000'05 !lItt il9'ìl ¿8f'tl ¿I6'0 I m0'0t 000'l ¡url¿ lt¡lrr..q ¡õllço¡¡r0 (¿t('rf (f¿('¿6 (¿01'16 (008'96 (106 fl (60('0s (59!'rl {ì5r'¿6 (9r6'¿¡ (50¿'9t .0'0) -t8t ¡t) .119.9) -66r't) -¿50'z) -698'¿t) -llt'0) .16l'9t) -919'r) -rtl'8) rn¡trl¿q ¡f9{ oæ'ot ' g¿¿'al 000'05 otf'ta gsf St 5t0'9r o0¿'¿l 000'09 000'16 ctu.6ro t¡l.¡¡qr¡ilqæ¡¡ro .-l¡ ¿.þ l¡t ..¿t,ÞÁ .{¡ a/ {rÞ¡r.{rl¿ r¡ r¡ú.¡u€ p¿ ¿cfd.q¡ ¿c.¡trt¡ Þ!r4¡sr tff pr ¡;ord u.* ru /9¡twr TABLE 68 The nrean percent of stomach fullness and 95% confídence limits over 2t hours feeding period. 400 800 I 200 | 600 2 000 2l{00 0steochilus hasselti' 2.2\3 58.231 20.448 76.910 97 .007 /- . >o> ( 0-46 . 559 ) (2q .802 -87. 586 ) ß.glt-us.zst) (47 .050-96.552) (z¡.4r9-r20.00) (o-6I.ot7) Tri chogaster pectoral i s 8t .622 ^ ^-f ¿{0 ¿. ¿>o 7tt. I 27.639 I 00.00 75.169 (rq.75rr-91.197) (0-60.8lt) (74.¡40-74.140) ß.202-92.164) (Ioo.oo-roo.oo) (l.oie-95. tut, Tr i chogaster tri chopterus 84. | 70 58. oo9 67 .959 ?ç l¡l¡? 83 . t9l $?.0\2-99.715], (20.353-90.857) (l 5.637-99.81'6) (0.tr80-69.7t2) (t t.938-86.7t0) Punt i us orpho i dcs 2.243 58.zlt 20.41{8 76.9t0 97 .007 ¿, >o> (o-46.559) (2\.Bo2-87.856) (3.971 -\s.25t) (47.050-96.522) (73.4t8-96.285) (o-6t.ot7) Puntius gonionotus 0.317 | 00.00 I 9 .000 I 00.00 93,888 q< ô(? (0-21.7t7) (l0o.o0-ì00.00) (r5.58r -93.243) ( I 00.00- I 00. 00) (65.006-98.23r ) $ . tsz-9g.ttt, Notopterus notopterus qo nÁo \\.526 36.000 98. 783 (go. lg0-roo,oo) (t6.389-7\.7\8) 99.93\ (0.998-85.974) ß2 .692- I oo. oo) (gz.gss-to4.oo) PristolepÌs fasciatus 9t .721 95.365 2r.498 9t .3\9 I 00.00 25.221 .982-96.728) (75.072-99.2t3) ,$t (0.666-59.649). (63.2t7-99.toz) ( r oo. oo- r oo. oo) (o .675-66.976) oxyleotri s marnoratus t 00. 00 59.2t9 71.43'1 o),5>, (roo.oo-Ioo.oo) 75.332 $.418-9e.755) (8. 056-9 7. 609) (15.77t-98.483) ( I 9.628-89.7¡ 8) Hampala nacrolepidota 40.849 I 0.000 I 00.00 o ool (o-lz.l 99.354 7t .393 tl) (82.839-r00.00) ( | oo. oo- ¡ 00. o0) (s . trSs-9e. 3q3¡ (0.583-28.825) 0phicephalus lucius 79.516 68. 898 58.682 60.32\ (44.656-e8.995) (30.948-95.96t 99.096 6l.oglr ) (2t .603-90.975) (26. t95-89.542) ß2.\\7- too. oo) (27.ì84-92.t63) 0phicephalus striatus /ó.ó/> 75.000 7\.210 I 5 .850 7s.870 61.¡gl (30.5r 5-99.907) (7.tte-y.r5r, (r2.8ì6-98.07t) fr f / \ | .t¿>-oo.J).1^^- ^^r\ ) ß\.929-99.2t9) (6. s8o-99 .893) 0ph.icephal us mi cropel tes 3t .767 6s.8¡l I 4 .644 6\.288 ¡ 00.000 8t .622 (6.993-98.888). (t.3t3-82. (12.253-82.1 t¡8) t8) ß.2ôh-98.798) (r00,00-t00.00) (0. +13- r oo. oo) (,H æ lÂgtE ncan perccnt 69 Thc añd 951 confldencc llmlts of the najor food contcnts ln stonachs of flsh In 2¡l hours fcodlñg pc¡íod. CONTENf 800 | 200 | 600 2000 2\00 0stcochilus h¿sseltli organlc dútrltus 0 \5.971 r4,7¿rl 29,997 lrt.482 (6. 0 5q2-88. 92 ì ) (t, iis- 37.967) ß,896-6r-.i | 3t ( 3, 09z_ Bs. 76r,) 0steochllus h¡sseltll Planr . 2:2\1 1.505 0.56{ 19.76\ 37.291 2.56s (0-20.8r8) (0.049-7.027) (0,020-t.841) (2,209_r[¡,5rt, (2.29r_8\'.185') (0-64:Si¡i Puntlq5orpholdes organlcdctrltus g.'\s . - 0,203 o:!!i o 0.265 ss.o2s (0-85.e28) (0-2.872\ (0-5.788)- (o-2.Birl-' tt.t'gi:églogtl Puntlus orpholdeg Plant . ^l?.9Þ . . 7'9\7 - 6.'t lì t,6tt7 so.B79 2\.297 (1.816-74.rq6) (o-5e.548) (o-6s.sz7) (o.s09-ii.;96) (¡¡.zio:ei.g¡s) fe.sÀd:õíirs¡l Tr¡chogaster pcctorôl ¡s Cru5!ãceån 11.270 0 - 2,565 (o-99.ej9) (0-6{.89¡)- pcctor¿lls orgênlc dètrltus .Tr¡chogðster _34.f882..565-o_75.t6g (0-57.9321 (0-64.894) ß.\3i_95-.\37) i lrlchogas!cr trlchopterus Crustðcean . 66.483 .. 0.6q5 - 5.278 25,\\3 (22.720-97.43i)(0-r0.895) (o,t2t-t7.2t6t. (0,¡to:io,í¡t) Trichog¡¡tor ' trlchoptc¡us organlc dctrltus \.27\ 9,662 _ 34. t88 _ (0,095-- o Notopte rus rotopteru5 I nsect ,^,.t"1'273^^,, o ' - 65.8rt 8.349 tu.{)¿Êo),Z¿Þr (l{2.067-t00.00) (¿,.S9t-52.?99) Notoptcrus notopterus Crustôccan 29,\78 il.6t4 l t .27o 8.8t 1 (0,933-89.733) (0-80.025) (o-99.9iti (o.zor{lià.4zsl Prlgtolep¡s fàsclðtus Inscct t6.5J6 2,266 o,tol 3.0t5 _ 2.2\O (f.820-68.314) (0.ì20-ro.93o) (o-r,228) (2,t,ti-22'.555\ (t.ì75_t5.82t) Prl!tolêpis fasclðtus Crustaccon 4.290 t6.8rr6 1 o.qtÀ 9.261 - 2.787 (2.223-28.8\71 (2.t5t-4t.37t) (0.t39-2.737). (0.127_30.28t) (t.69t_20.t82) Prlstolepis fasclðtus 0rgðn¡c dctrltu3 . 2\,932- 10.997 8.il2 5o.3to _ 4,271 (7.370-92.868) (0.007-39.99t) (1,470-4t.425) (13.933-86.494) (o_45.Soir) oxyleotrisffirclat!s Flsh 97.630 ^ 3\.5\9 \,827 4.823 33.3ì4 (46.5ô6-ìoo,oo)(t8.t36-98.429)(o-63.9t3) (o-55.0¿3) ßt.i;7:%.573') Oxylcotri s roniolatus Crustocean - 2,369 0 49.999 \7.986 2.902 (0-51.r¡r4) (5,79e-9q.200) (o.i3t-9B.9ee) fo_q¡.óíoi ophlcephalusluclus Flsh . 25-,253 48.7ìt 25.OOO 17.256 \6,lle 1r.52? (0,048-73.780) (3.6t5-95.36t) (0.540-Bt.5B7) (0.4t!-6i.lzz) (rZ.oÀò-lZ.g¡e) (r,,,¡z-í2,soe) ophlcêphalusluclu3 Insec! _ .0.615 0 3.0t5 0,085 0.98t 2.A\7 (0,030-22.826) (¡.loã-zg.zss) (o-0.õóõi- (o.ooã-¡.¡o¡) (o-2q.035i ophlcephalus luclus Crustaceðñ 0 0 3.0t5 2.À04 2\.738 4.082 . (5.r06-29.758) (t,t02-16.374) (4.503_54.t85) (o.oì?-t7.759) ophlcephèlus striatus Flsh _ - 69.068 75.000 \9.999 6.698 2o.g\5 o (r6.5r3-99.925)(o-roo.oo) (37.3r,7:¿i.6s2)(0-6\.72i) (o.tn-Zo.eeù ß.76i-9s.537) ophlcephalus strlêtus Crustôccôn 0 0 0.3t7 0 7.OOt o (0-5.456) (0.237-30,\32) 0ph¡cephðlus ñlcropeltes Flsh - -r3:o!? 49.999 14.644 \9.999 - \9.999 (0-85.806) (s.237-e\.762\ (o-9e.lreo) (y.tit-øL.asù ß.ui:ií-.7621 (,H \o 140 DlSCUSSION success ion staqes The reservoir conclitions differed in both flora and fauna, according to the successional stage. The grass-covered habitat which establ ished along the littoral area represented the reservoir early stage of succession, subject to abiotic stresses such as, flood, waves, currents, temperat.ures and f ight fluctuarions ('dum, r97r; Regier and l'enderson, lg7Ð. The weed- covered habitat, charactei¡zed by dense mats of obnoxious aquatic and semî- aquatic plants, represented the reservoir late stage of succession. The open-water habitat represented the intermediate zone t. There are 40 specíes of aquatic macrophytes ín Bung Boraped (tanl e 2). Leersia hexandra, Hymenachne pseudoiterunl and cynodon dactylon are the domínänt specíes in the I ittoral zone. Eighornia crassípes, salvinia cucul lata, lsachne globosa and cyperus cephalotes are the most abundant species in the Lleed Area. C. cephatoles . and f. qlobosa which can form a sudd community (Boughy, 1963, Mlchell, 1969 and Junk, 197Ð with other plants, conrribured considerably to the formation of floating islands There were níne specîes of aguatic and semi-aguatic macrophytes in the Grass Area (Tabiu:¿). Among these the percentage cover for L. hexandra, -J4.72, !-. É..tyt"L and H. pseudoite.rum was 5.06 and l.l3Z respectively. L' hexandra was pioneer the species in the Grass Area and was slowly replaced by H' pseudoiterum and c. dactylon as the water level in the littoral area receded in February' túith rising water levels in september, the population of hexj¡ndra !. that had survived the dry period (May - August) increased, and the plants grew up vertícally and kept their roots attached to the sediment. L' hexa¡5lra can survive in the water for many months as long as some part of the stem and leaf is above the water level. In February, after the water level r-1., l:.f:j... -.:..-:.:.:.:.-:.:.-1:J...i".-l1. i ¿?¿1 1,1 in the littoral area dropped to 0.5 m and the water temperature rose to -lì 34-C, H.pseudoiterum started to expand its population. In March C. dactylon încreased and occupied up to 44.11% of the Grass Area. 9. dactylon can survive the very warm climate and drought, unlike L. hexandra which is very sensitive to dryness and started dying after the water level receded in summer. As the water level began rísing in August with the start of the rainy season C. dactylon became completely covered with water and died within a few weeks. There In/ere ten speci es of aquat ic macrophytes in the t/eed Area (TaU le n). E. crassipes, S. cucul lata and l. globosa covered 28.30, 14.20 and 8.957" resPectively. !-. crassipes and S. cucullata, which have loose structure and unstable formation, were the pioneer species and later were displaced as they provided a substrate for other symbiotic species such as Cyperus cephalotales, CyPerus difformis and Fimbristylis miliaceae. E. crassipes and S. cucullata appeared to be quite susceptabìe to the heat during summer, resulting in a decrease of population which created an opportunity for the advance of C. cephalotes. E. crassipes and S. cucullata expanded very rapidly during the monsoon season with the rain and the inflowing river water (Junk,1973). The expansion of C. cephalotes showed a negative correlation with S. cucullata which had been its substrate. The increase of C. cephalotes caused S. cucullata to lose its buoyancy which resulted in either sinking or breaking up of its mat. C. cephaloles survived because its roots were already attached to the lake bottom and the density of the plants enabled them to remain standing. !. globosa was the most successful floating macrophyte. lt advanced from the inner side of the l,/eed Area near the shore into the lake as soon as the mats of other macrophytes were thick enough to be used as a substrate. Near the shore they became deeply rooted in the ground but in deep water they formed thick f loating mats with H,rS present under the older stands, as previously descri bed. r42 Aquatic macrophytes affect many asPects of the morphology and biology of reservoirs. Their Presence in dense mats may impede or completely prevent navigation and recreational uses and promote loss of water by transpiration. Largè amounts of aquatic plants may create deoxygenated conditions in which fish cannot I ive and make fishing operations difficult or impossible. 0n the other hand they may provide suitable habitats for spawning and feeding of young fish as weìl as for invertebrates that serve as food for the fish. Penfound (lg¡6) reported that aquatic macrophytes are of considerable value to small aquatíc animals since they provide them with shelter, food and oxygen. He pointed out that the productivity of animals in an aquatic environment varied with type of aquatic plant and ¡ts influence. Smirnov (1963) has studied the distribution of the inshore Cladocera of the Rybinsk Reservoir on the Volga. He found that in the aquatic vegetation area near shore the abundance of fauna was several times that in the non-vegetat¡on êreas. Mclachlan (1969) reported that rooted littoral aquatic plants affect the productivity of the zooben-thos. He found that th'e presence of Potoamogeton pusi I lu:. Ludwigia stolanifera and Ceratophyl lum demersum in a newly created tropical reservoir, Lake Kariba in Rhodesia, resulted in an increase in the biomass of benthos with the appearance of several new species. Boyd (1971) stated that emergent p'lants are usual ly more productive than submerged and f loating plants. Lim and Furtado (197Ð also pointed out that aquatic macrophytes are known to be important in increasing the productivity of the aquatic ecosystem- The species composition and character of aquatic plants are rel iable indices of the hydrobiological regime of the r¡rater body. Balon and Coche (lgZ4) conducted a fish production and iimnology study on Lake Kariba, Rhodesia, during the period 196|+ - 1974 and reported that þ!¡{na auriculata and Pistia slggioteswere the most common among the f ree f loating hydrophytes, L43 that Panicut Jepglrs and Ludwigiq stoloniféra were growing along the shore- I ine,and that Cer-ajophyl lum qgglgg¡n Potamogeton pus i I lus and Naja sp. were the common submerged hydr"ophytes. Boughey (1963) observed the "Sudd communityrrin Lake Kariba (a floating colony of plants resulting from the colonísation of a stable mat - e.g. Salvinia mat - by other vascular plants). Junk (tgZO) in his study of float¡ng meadows in the Amazon region found that Eichornia crassiLes, Pìstia strat¡otes, Salvinia auriculata and Jussiaea.natgns are the most common float¡ng plants in the Amazon river and its tributaries, and Mari (fgZO) reported ín their hydrobiology study on South East Asian inìand waters that Utricularia Nyphoidesj:'di.* ilg, "nd Trapa sp. are the common floating plants in the Tasek Bera, in Malaysiã. Lud¡riSia stiputacea, Flagel laria indica, Lepieonia artículata and Eleocharis ochnostachyl are also reported to constitute the floating hydrophytes in that area. Because of their abundance the aquat.ic macrophytes play an important part in the filling-in of the reservoir. The large quantities of organic detritus produced annually by them can fill in the reservoir basin very rapidly. Holm, hlildon and.Blackfure(1969) reported that in canals covered with Eichornia, 30 cm and more of detritus accumulated per year. The wind direction during the monsocn is usually constant for several months and this favours the f¡ll¡ng-in process in areas exposed to wind. Detritus banks were observed in many areas along parts of the reservoir shorelÌne that were exposed to wind. The bank was immediately colonized by macrophytes, parti- cularly Scirpus grEE, Cvperus cephatotes and Coix aquatica, whose roots stabilized the loose material. From this point of view, therefore, the most u.ndesirrable species are those which rooted in the substrate, part¡cularly C. aquatica. This species can advance far out ínto the lake because of its semi-floating habit. lt forms very thick mats of roots and stems which only L44 float away in small masses and are resistent to wind and wave action because of thefr robust habit. In addition the areas of water on its leeward side are protected from wind action and form ideal habitats for less resistant forms. ln such areas there was a strong tendency for sudd 'formation by S. cucullata and C. cephalotes. They are important to the f¡ | I ¡ng-in process because of the production of large quantities of organic material. The soil samples showed that the l,Jeed Area and the Open l^later Area had low organic sediments. The organic matter in the Grass Area, .. the þJeed Area and the Open Water Area was B.\4%, 4.06'Á and 4.30% respectively :::': (tables 19, 20 and 2l). The greater amount of organic matter in the Grass Area was due to the effect of the established grasses. They reduced water movement and thereby caused the sedimentation both of the organÎc detritus, which was rapidly mineral ized, and also of the f ine inorganic material which is continuously brought into suspension during the high water period. The smaller amount of organic matter in the Weed Area and Open Water Area was probably due to the severe turbulence during the monsoon which kept the deposited material stirred up. This turbulence also explains the low I ight i,¡ penetrat¡on through the water and the fact that the water is oxygenated down to the bottom. .".'; Several factors counteract this autogenic fi I I ing-in of the reservoir bed. The remineraì ization of the organic material occurs very rapidly because of the high temperature throughout the year. The process is enhanced .::: .,-t, by the frequent wind-induced water movements. A significant part of the organic material drifts out of the reservoir in the form of floating vegetation mats and also as fine detritus. The'annual h,ater level fluctuations strongly hinder the development of aquatic and semi- _: tt,, '"r' aquatic vegetation. L45 Dur i.ng the | 0 month per iod the water qua I ity in the Weed Area ,,, -,..t..,,,, appeared to be the poorest (20.5 ns/l of dissoìved C0, and l'5 nS/l of dissolved 0.,)¿¿ when compared to the Grass Area (20.0 mgll of dissolved C0. and 5.3 ns/ I of dissolved 0r) and to the Open Water Area (l¡.S mg,/l of dissolved C0^ and 6.8 ng/ I of dissolved 0.,). ln the l,/eed Area the z ' z :.'.,.:.::. "::":1:'' decomposition of organic.materials within the mats of floating vegetation was extremely high and the mean conductivity was l\7.6 micromhos. During the summer months the decomposition was at maximum (2\.5 mg/l of dissolved .t.. . :.'. Several floating weeds withered ancl died, resulting in a depletion :;,.;,,;..'.- C0^).--2' " t -"; ".:..": of oxygen which prevented many aquatic organisms from inhabiting the area i::.:t:t:.:::. a.-: :..:::... ::: .1.j: (1.5 mgll of dissolved 0r). Because of the large amount of area.covered and the intensive decomposition of floating vegetation, particularly during the hot and calm summer months, it is possible that most of the oxygen in thelakecouldbeconsumed,therbyaffectingmostoftheaquaticlife. Massive infestation of f loating weeds rnats must therefore be avoided' particularl'' during the summer months. ln the rainy season the oxygen depletion under the vegetat¡on stands may not be very severe because of the prevaiìing monsoon winds and the resulting turbulences The annual water level f I uctuat íons keep the f loat ing forms under ',,',;',',;',',':i.,:;-',:,, : . 1 ... - 2 ' 4 m is insuf f icient control to some extent but the natural amplitude of :.r,::.,::,,:,,:,, :::: :'' ;: for effective control. lt is recommended that the art¡f icial water draw- down should be carrie out annual ly, and during the summer months. The reservoir must be partly dried in order to kil I the f loating vegetat¡on. .jj.:..:.,::,::, j.r i:':::' Af ter ref i I ling, the water level should be kept high for long enough that the drying vegetation mats become detached from the bottom and float. lt is then possible thaf- they wil I drift out of the lake area during h¡gh u/ater levels along with free floating hydrophytes which have been torn loose L46 2, Jhe developmen!of benthic organisms-. [n all three study areas the Insecta were the most abundant. 0l.igochaeta were second, Mollusca third and Crustacea fourth. The multiple corer appeared to be unsu¡table for col ìecting the larger Mollusca and the mobile Crustacea, such as freshwater shrimps and crabs. Chironomidae and 0ligochaeta were the first to populate the Grass Area. This occurred in September soon after this habitat was established, after flooding in the rainy season. lt is similar to the observationsof Petz (lg6g) in volra Lake in Ghana, and Kryzanek(lgzo) in the Gsczalkowice Reservoir in Poland. The greatest number of Chironomidae were found in November, possibly because of high oxygen concentrations during the high ftood period. D¡ptera and Coleoptera were second in the formation of the benthic community, fi rst appearing in 0ctober. Planorbidae, Ephemeroptera and Odonata first appeared in December. Ampullaridae, Copepoda and Qstracoda first appeared in January. The benthic organisms in the Grass Area built up their population from 0.88 n/core in November to a maximum 2.25 n/core in February and then declined slightly in March and April (Z.OZ and 1.99 n/core respectiveìy) as the water receded. The Grass Area was dry from Hey to August. 0ligochaeta and Chironomidae became re- established in September after the littoral grass area was flooded. Hynes (lg0l) found that in Lake Bala, England, the fauna greatly changed after a. water ìevel fluctuation, and the of 0ligochaeta increased greatly on the exposed shore' Fillion (1967) stated that the abundance and distribution of benthic fauna in Barrier Reservoir, Alberta, were affected by water ler¡el fluctuations. He found that the benthic fauna was far more abundant in the vicinity of drawdown | 'lmi ts than e I sewhere. '.:.: L47 tn the Weed Area the mean density of benthic organisms were the ,,,,,,,. lowest (O.ga n/core) of the three areas. lnsecta was the dominant group' with Mollusca second and Oligochaeta third (faUtes 36) . Petz (1969) reported that snails formed a substant¡al part of the benthic biomass in regions of reservoirs with abundant aquatic plants. The numbers of benthic organisms in the Weed Area showed a negative correlation .ir,,. with the development of lsachne globosa. This plant formed thick floating mats in which HrS was present inside the margins. Aquatic fauna could only develop at the upper surface where oxygen Îs suppl Ìed by exchange w_ith the ..: . and by aìgal assimilation, or just belorv the mats where some oxygen is air :,: .: -:':: present from horizontal water exchange. The number of benthic organisms decl ined as the mats of floating vegetation became thicker and started to sink to the reservoir bed. This normally occurred during the summer months when the water level in the reservoir was at its lowest stage, thus having an even more serious impact on the productivity cf be'nthic fauna which live under the floating vegetation. At this time the water quality underneath the mats of the float¡ng weeds ís extremely poor' The benthic population appeared to increase greatly after the fìoating reached a peak weeds drifted away with the tropical storm in September. They ,j',,.,,. in gctober (2.03 n/core). and then dropped slightly in November and December. . ''''' This suggests that the low oxygen concentration under the thick f loating weeds had a negative impact on the bottom fauna below' ln the gpen l./ater Area the mean densïty of benthic organisms was l.4Z n/core, lnsecta were the most abundant with Ol igochaeta second and :l'. Mollusca third (faUles37). The larvae of Chaoborus sp. occurred in the greatest number (0.23 n/core). This insect follows the mobile plankton at night and stays close to the bottom sediment during the day. Corbicula siamensis appeared to prefer the hard bottom of the 0pen \'Jater Area to si lt ..:.. 148 deposits of the Grass Area or the Weed flrea. Chironomidae and 0ligochaeta peaked during June to August when favourable environmental conditions existed, such as maximum dissolved oxygen, minimum carbon dioxide content and opt¡mum pH (fa¡te 9). The densities of benthic organisms dropped drastically in September due to Poor water quality which occurred because of flooding from the Chao Phya River' A comparison of the bottom fauna among some shallow reservoirs in Thailand is gíven below. The overal I cl imatíc condi tions of these reservoirs are simi lar but the topographic and I imnological L characteristics of each reservoir are different, particularly the ages of the J. impoundments. Kaeng Krachan Reservoir was built in 1966, Lampoa Reservoir in 1968 and Lam Ta Kong Reservoir in 1969 (VJaewngarm, 1970; Srisoowanatad' 1970 and Sunkagul, l97l). ? :t - - -:k>k :!:k;'r NUMBERS/m' OF KAENG KRACHAN" LAMPoA LAM TA KoNG At I Benthos 2go.5oo 3 92.75 688.60 Ch i ronom i dae 206.60 l4t+.7 5 314 .? BUNG BORAPED HumseRs/m2 or GRASS AREA I,'EED AREA Al I Benthos 709.09 4gt .tl :'-:1::) . ::1..: ..j ï ronomi dae r 80. 34 ': . .. _.. ...' l Ch 30.05 t'lr,""*ng"rm (1970) '*t'srisoowanatad (lgZo) "t"* sunk"gul (lgZl) The densities of benthic organisms were highest in Lam Ta Kong Reservoir and lowest in Kaeng Krachan Reservoir. lt is clear j.': -!- 1.:.1.:: '::-,.::.'.,'":: - --r .' : I ;::i' '::.:¡.:::."1::ì:"i.::r.;.lti.:'ì :ï:ri.ì::¡:: L49 that the abundance of benthic organIsms is correlated with the age of the impoundment. In this study an early succession stage region represented by the Grass Area showed higher densities of benthÎc organisms compared to the late succesSion stage region rePresented by the Weed Area. Therefore any practices that could alter the succession stages by bringing back an early impoundment stage or early stage of succession should beappì ied in order to restore the benthic productivity of the reservoi r. 3. The development of invertebrates associated with aquatic macropjrytes In the Grass Area Indoplgnorbis exustus F. Planorbidae and Pila ampul laria were frequently associated with L. hexandra. Ephemeroptera, Trichoptera, Coleoptera and Diptera were found in large numbers in L. hexandrarH. pseudoiterum and C. dactylon. The mean numberdof invertebrates associated with L. hexandra, H. pseudoiterum and C. dactylon were 23.98, 3.36 dnd B.l5 n/f¡andful respec*tively. The densities of invertebrates associated with those three major grasses decreased when the water receded \ and the grasses decomposed, producing unfavourable conditions such as low oxygen concentration. During the high water phase (December 1974 and January lg7Ð invertebrates were very abundant in L. hexandra (40.30 ana 46. l8 n/handful , respectively) indi cat ing that water level variat ion was the factor complex that affected the presence and abundance of organisms in the vegetation (Junk 1970 and 1973). These factors can have a selective effect on the fauna of the aÇuatic vegetation. Those forms are favoured which have a short life cycle and a high reproductive rate. The floating vegetation was found to be a favourabìe biotope for most invertebrates. Trichoptera, 0donata, Coleoptera, Hemiptera, l_50 potamidaé and paleopteridae were widely distributed and abundant" Copepoda and gstracoda wefe found, but their contfibution to the -total biomass was not signifÎcant because of their.small size. The population density of invertebrates in the l.Jeed Area was by far the highest in E. crassipes with 21.06 n/handful. l. globosa was second and S. cucu]_lata thi rd with 13.06 and 7.27 nlhandful respectively. The species of animals which occurred on the floating vegetation and thei r population densi ties were dependent on two factor complexes, the type and morphological characteristics of the vegetation layer, and the physico-chemical properties of the sur- rounding water bodies. ln very loose vegetat¡on the anÎmal poPulation densities were relatively low. ì,J¡th increasing thickness of the vegetation the number of invertebrates also rose. The. fluctuations in mean number for each handful of invertebrates associated with l. globosa, C. cephalotes .and S. cucullata appeared to be quite similar. The population of inverte- brates in l. crassipes appeared to correìate with plant develoPment. The number of organisms increased as E. crassipes expanded its population during the wet months and decreased when plants became withered during the dry months. This s.uggests that among the floating macrophytes E. crassipes is a favourablu biotop" fo' invertebrates' The degree of horizontal entanglement of stand was relatively weak so that better gas exchange between ai r and uJater l^/as possible. The densities of invertebrates associated with C. cephalotes, S. cucul lata and E' crassipes reached their highest peak in September, reflecting the impact of rain ' upon pla¡t development, and indirectly on assosiated fauna. The inverte- brates in !. globosa also showed the same pattern,but to a lesser degÉee, probably because of the greater density of plant matter. There was a marked diiference in density of fauna when sampling from different places in a stand. The densitfes were greater at the margin than at the centre. The 151 difference was very evident, pârticularly ¡n stands gf l. g]obosa vlhich formed dense mats of roots, stems and dead material to a depth of 50 - 60 cm beneath the b/ater surface. The stabilIty and structure of each plant species stand also determines the abundance of fauna. The temporary breakdown of the loose stand in some plant species.into small cìumps could markedly reduce the protection offered by the plants to the different animal groups. This may explain the lower abundance of inverte- brates associated wíth S. cucul lata and L. iephalotes,, but such breal.:down would probably make conditions better for larger organisms, such as fish, in that the conditions for circulatíon of oxygen would be better. 4. The species cornposítio¡ of fish and production. According to the fish landing stat¡stics the total catch decreased fron862,445t Trichogaster pectoral is, ê planktivore, and AnaÞas testudineus, an insectivore, increased in numbers but the predaceous and piscívorous fish such as Ophicephalus micropeltes, Kryptopterus bleekeri_, Wal lagonia attu and !al lago dinema decl ined in number. The increase in abundance of planktivorous and insectivorous fish after water level manipulation represented increasing populations of the short food chaÍn species. l,Jood (1950 and l95l) described these fish as the expanding fish population which are characteristic of new impoundments. l./ood, Roberts and Booth (lg4Z) concluded that to restore an expanding fish L52 extreme drawdown was necessary' populationr ê Periodic .,, The species compositions of fish before and after the water drain- ing manipulation were dîstinct (fable 70). In 1969 PuntiÚs gon¡olotus' 0phìcephalus striatus, Puntiopl ites proctozysron, Cyclochei I icthys enoplos and Mystus nemurgs were the most abundant, making up ll.05, 10.10,8.92, 8.08 and 6.88% of the total number respectively. ln lgTl (one year before the '," draining operation) the total catch was lowest. 9-. striatus, one of the top carnivores.contributed the greatest number to the total catch (l l.3l%). l. gonionotus, P. pro.to=yrron-, C. enoPlos made up 10.39 , 8.56 and 7 '22'Á respectively. ì,lal lagonia attu, another top carnivore, was the f ifth in , l percent contribution ro the total catch (S.lSÐ. The great abundance of top carnivorous fish such as g. striatus and \^/. attu characterized the structure of the fish community (Swingle, 1950 and Tang, 1970) and the lower production of fish. The top carnivores terminate the longest food chain, so that the energy turnover is lower compared to the shorter food chain herbivores (0dum, l97l and RegÌer and Henderson 1973). ln 1973, after v,,ater manipulation, the herbivorous P. gonionotus and Puntioplites proctozysron were found to be the most abundant (8.S5 and 8.077o respectively). 0. striatus decreased f rom I 1.31% in lgTl to 7.767". C. enoplos and t^/. attu made up 5.93 ' , and 5.Bl% respectively. The total contribution of the top five species : . . ..: .:. 1":: (P. gon.ionotus',, P. pro.to=yrron, 0. striatus, C. enoplol and l'1. gL!u) decreased f ron \3.267. in lgTl to 36.52'Á in 1973, whi le the percent contribution of miscellaneous fish groups (comprised from species that contribute less than 0.57. to the total catch) increased greatly f rom 2-86'4 in lgTl to 17.l I in . . 1973. This increased diversity suggests a readjustment of species composi tion appropriate to the new environment after the draining manipulation. ln 1975 four of the five most abundant species came from the miscellaneous group. 0steochilushasseltii,F.CyprinidaewasthemoStabundant(|6.22.Á),and TABLE 70 The specleg composltlon by nur¡ber of flsh In Eung Boraped, from landlng statlstlcs ln 1969' l97l' 1973 and 1975*. | 969 I 97t 1973 | 975 Ft sH sPECr ÊS FI SH SPEC I ES FI SH SPEC I ES FISH SPECIES Puntlus gonlonotus 11.05 Ophlcaphalus strlatus ì1.31 PunÈlus gonlonotus I .gs 0steochi I us hasseì ti I 16.22 0phlcephal us stri atus 10. l0 Ptntius gonlonotus 10.39 Punt lopl I tes proctozyron ' 8. 07 Ophicaphalus strlatus 10.62 Punt lopì I tes proctozyron 8,92 Puntloplltes proctozyron 8,56 0phlcephal us strfatus 7 .76 Cl upeol des hypsel osorna 7.98 Cyclochel I lcthys enoplos 8.08 Cyclochel I lchthys enoplos 7,22 Cyclochel | | cthys enoplos 5,93 Lablobarbus I lnlatus 7.05 Hystus nemurus 6.B8 lfal lagonla atÈu 5.75 Wal lagonla attu 5.8 ¡ Pri stolepl s fasclatus 6.36 l,?al lagonia attu 6. ¡ 5 Mystus nemurus 5,66 Hystus nemurus 5.7t1 0phl cepha I us mlcropel tes 5.92 Clrrhlnus mlcroleols 5.68 lttorul lus chrysophckadlon ¡1.91 Wallago dinema 4.91 Puntlus gonlonotus 5. BB Horul I us chrysophekadlon 5,29 oxylcotrls mamoratus \.67 Notopterus chltala 3.92 Mystus vl ttatus 5. B0 Pong.aolus sutchl \,52 Clrrhlnus mlcrolepls 4.58 0steoohl lus melanopleura 3,65 0phlcephalus luclus \.lt 0stcochl rus mel anopl eura 4.40 Notopterus chltala q,3l Kryptopterus bleekerl 3.63 Cyclochel I lcbhys enoplos 3.15 Notooterus chl tala ll.4o 0phlcephalusmlcropeltes \,23 0phlcephal us mlcropel tes 3.60 Notopterus notopterus ¿.>o llal,lago dlnema 4.20 0steochl I us melanopleura 4. I 0 Moru.l I us chrysophekadion' 3.56 Clar I us bratachus 2.27 Kryptopterus bleekerl 3.84 Pseudo5claena sol dado 3,52 Pangaslus sutchl 3.40 Oxyleotrfs mamaratus 0phlcephalus mi cropel tes 3.38 Kryptopterus bleekerl 3.00 Oxyleotrls mamoratus 2.99 Fluta alba | .79 Oxyleotr¡ s mamoratus 3.27 Pangaslus sutchl 2.94 Pangaslus larnaudl I 2,69 Anabas testudl neus I '7tl Pseudc¡sciaena sol dado 3,12 Wal lago dlnema 2.9t1 Clrrhinus mlcrolepls 2,63 Trlctiogaster pectoraTl s r .66 Pangas lus larndudl.l 2,57 Hampala macrolepldota - 2,90 Pseudoscfaena sol dado 2.\\ Horul I us chrysophekadlon I .,{) NotoPterus notopteru9 I .38 Pangasl us larnaudl I 2.64 0phlcephalus luclus t.28 llotopterus ch lta I a 0 .88 Datlnoldes mlcrolepls l.28 Datnloldes mlcrolepls 1.63 Datlnoldes mlcrolepls 0.98 Punt lopl I tes proctyzyron 0.76 Leptobarbus hoevenl 1,28 Notopterus notopterus 1.56 Notopterus notopterus 0.85 Trlchogaster tr¡chopterus 0,52 Hl scel laneous O.zf l'tl scel laneous 2,86 Hlscel laneous I 7.1 | Ml scel lgneous r0.39 TOTAL LANDING 535,455 Kg TOIAL LANDING \67,522 kg T0TAL I-ANDI NG 678,598 ke TOTAL LANDING 723,0q8 ks t From Nakhon Sawan Flshery Statlon Annual RePorts 1969' l97l' 1973 and 1975. (¡tH u) L54 0. striarus was second (..l0.62%). clupeoides hypselosom3 F. clupeidae, Labiobarbus ì iniatus F. Cyprinidae and P,rîstolepis fasciatus F. Nandidae were f .j8r 7.05 and 6.102 respectively. l. gonigqotus was the seventh in abundance (5.88%) and W. attu was classified as miscellaneous because the percent contribution was less than o.5oZ. The increase in abundance ,,,,,,1,, of herbivorous f ish (L. hassertii, L. I iniatus and p. gonionotus) and planktivorous fish (!. hvpselosoma and p. fasciatus) after the water level manipulation indicated an increase in the populationsof the short food chain species which are characterist ic of new impoundments. .:'.."'' The average weight of fish caught from the Grass Area, the l^/eed ,t,l.,l Area and the 0pen water Area were 6l.lg, 27.13 and ¡8.99 g, respectively. The high contribution of paralaubuca sp. in the weed Area (24 2.7 "n¿ in the 0pen l./ater (37 Area Z). may , be responsible for the low mean weight. Smith (lgt+S) described Paralaubuca sp. as a smal I f ish which reaches full maturity when lO - 15 cm long. : The top carnivore fishes such as Ophicephal_us micropeltes, OphicePhalus striatus, Oxyleotris mamoratus, Ompox bimaculatus and Wal laqonia êttu were most abundant in the weed Area than the Grass Area or the open ,.:., Ì'/ater Area' The herbivorous and insectivorous fish such as puntius orphoides, ', ;' Horul ius chrysophekadion, Labiobarbus kuhlii, Trichogaster pectoraì .,.. is, --.-: __ Pristolepis fascíatuå and Anabas testudineus were more abundant in the Grass Area than in the l'/eed Area. The versati le planktonic feeders such as Paralaubuca sp., cyclocheil ichthys enoplos and cirrhinus microlepis were ,.,,:,'., far more abundant in the Open t/ater Area than in the Grass Area or the LJeed Area. l-55 It should be possible to increaie the desirable fish species such as the short food chain herbivores by creating a grass-covered habitat throughout the shal low area of Bung B.oraped by water level manipulation. and Puntius sp., Morul Ìus sp., 0steochilqq sp., -0:P.hrgnemus sp' Labiobarbus sp. are such desi rable species. Margalef (1964 an¿ 1969) stated that a relatively shallow lake subject to seasonal turnover or entry of sPate water wi I I have a very ìarge concentrat¡on of relatively short-l ived opporturnistic species and thus wi.l l have relatively low diversity, low stabil ity and high ecologi cal production. To maximize fish production in order to pl'ovide a protein supplement for the people, conditions opt¡mal for herbivorous species the must be maintained. carnivores such as ophicephalus sp., which are reduced most economical ly valuable species, must however be drastical ly vegetêtion in numbers under these conditions. The el inlination of float¡ng population' by summer drawdown wi I I indirectly control the carnivorous fish because this type of vegetation is their preferred biotope. Technique to restore the reservoir productivity ;;,, l. Water level manipulation ,:,,, of the water level in a reservoir has a profound The manipulation "" effect on the production of fish ánd the composition of the biotic community. The extent and timing of the increase or decrease in water been described as one of the Ievel may vary.. f^Jater Ievel manipuIation has i',,. (Bennett 1967, fishery management techniques by several . invest¡gators Jenkins 1970 and Bhukasawan lg73). They reported that the improvement of fish stock is similar to that experienced following initial impound- ment and usually lasts from one to four years : i:).;.t l --"'--f L56 [n Hay 1972 Bung Boraped was par-tly drained, excePt for the old stream channels and certain deep areas, for one and a half months' ln the interval before the monsoon raîns refilled the reservoir natural grasses, PartÌcularìy Leersia hexandra and llymenachne Pseudoiterum, became establ ished in most of the drained areas. These grasses were observed to survive in the rnater for several months after the refiIIing by monsoon rains. Floating vegetation such as Eichornia cr,assipes, Salvinia cucul lata, lsachne globosa, CyPerus cephalotes, Coix aquat¡câ and others were left to dry on the lake bed. They idecomposed after the refilling. In September the reservoir water level returned to its normal storage capacity. The floating vegetation was observed to have almost total ly disappeared. Quennerstedt (1958) found that a fìuctuation of water level of only J m in Lake Hotagen, Sweden, during winter had caused a disappearance of the rooted vegetation and all vascular plants. Runstrom (1966) noted that higher water levels in surpmer and the draining of Swedish lakes during winter caused the disappearance of aquatic vegetation. Lantz (1964) stated that aquatic vegetation had been greatly reduced due to the water drawdown in summer. Junk (lgZO) reported that in Amazonia the huge water level fluctuations of up to 16 m and the immense changes of water surface area were important controlling factors upon the floating vegetation. This natural control system can be art¡ficially reproduced to a certain extent in Bung Boraped and in other reservoirs and thus lead to a significant reductioni of fIoating weeds, as has been shown in Lake .l970) Kariba (M¡chell, 1969; Magadza and the Ubol Ratana Reservoir, Thailand, (Junk 1973). l,tood (.|950) reported that certain species of wildl ife occur in :iii :.1.r-'-: :.: ;.1.;-.: j-: :, :. ,::: ::l'j. . _:. .. . -,. L57 and greater abundance duri.ng some st.ages of plant succession' Penfound few Schneidau (1945) expressed the opinion that in wetland areas, with exceptions, any practice which will Prevent or retard aquatic succession or return it to an eaflier succession stage will result in an increase and in aquatic wi ìdl ife production. odum (lgZl) concluded that estuaries intertidal zones are maintained in an early, relatively fertÌle stage by the tîdes, which provide the energy for rapid nutrÎent cycl in9' Hulsey is (1956) and Bennett (1967) stated that fish production in a reservoir age' always productive at the early stage and declines with reservoir Eschmeyer (lg4Z) as cited by ¡lood (1950) v,,as convinced that highly extensive water drawdowns for flood control in TVA reservoirs were beneficial for fish. Hulsey (1957) reported that fol lowing fal I and a large winter drawdown of the Nimrod Reservoir and subsequent refilling' increase of young largemouth bass and whitebass occurred' lJood and Rivei Pfitzer (1960) stated that permanent level pools in the Tennessee i provided systemrwhich had been impounded for recreat¡onal purposes, poorer fishing than reservoirs which had water levels subject to wide fluctuations. Bennett (lgS4a-b) reported an increase in some game fish populations in Ridge Lake, I I linois, from draining the reservoir during Nimrod summers. t'lood and Pf itzer (tg6O) concluded that in 0ld River Lake' Reservoir and Norris Reservoir of the Mississippi River the productivity, species composition and ratio of predator to forage fish was influenced each of by water level manipulation. They e; drawdown in some litto¡'al areas of Bung Boraped. This natural establishment is small andthe contribution to the reservoir productivity is not substantial. The practical application of managed water level fluctuation would expand the grass-covered habitat in Bung Boraped. l.J¡th rising water level in September the grass will grow up vertically and increase its population very quickly. The rate at which the water level is raised should be controled so that L. hexandra can grow up vertically above the water surface during the early flood period. !. hexandra can survive in the water only if most of the leaf is raised up above the water surface The grass-covered habitat created by the water level manipulation in Bung Boraped should accomplish the following: 2.1 !ry.gl". tt¡t f"tt¡tttV ÙJhen the water had receded during the summer months and the littoral L59 afea WAs Ellowed to dryran abundance of oxygen became available, The process of decomposition and the pH of the bottom soil both increased. ...:: Under these conditions there may be a release of certain ferti I izing substance from organic col toidal partícles (Bennett , l967). The organic matter and nutríents of the lake sediment which are utilized by some of the benthic species, ,are mineralized. This remineral ization of the o.rganic'material not only occurred during the summer dry months but also took place throughout the year because of higher temperatures (Junk, 1973) in the Grass Area than the l,leed Area and Open Water Area. This remineral ization is bel ieved to produce a posïtïve economic effect because of increased fish production (Lel lak, ]969). The. organic content was hiqhesthighest in the Grass Area (8.842)(B.B4Z) and I signif icantly different (p (0.0.l) f rom the Weed Area or the Ope.n \,Iater Area. The organic matter uras highest in the Grass Area because of the decomposîtion of the establ ished grasses, and also because of heavy . sed_imentation within the I ittoral zone related to the water level varïation. .The organic matter appeared to accumulate more rapidly in tFre Grass Area .,,:, because of the 1ai¡d-protected character of the grass habitat. Entz (tge6) .:':' reported that organic material was observed to make up to 30. 4O'/. of the ì:, ' dry weight of substrate f rom the r.rind-protected shorel ine of Lake Balaton was rich in eme.rgent plants. .which organ i substances rel eased 0duq ( I gZl ) suggested that the c ,':, i -' into the environnrent Curing decomposîtion may have profound effects on the growth of other organisms in the ecosystem. These substances may be ,.i - ;T stimulâto¡y, ¿5 in the case of vafiouq yitamins and other grovúth substEnces. 0steochî Ius has:glt i i , Morul ius chrisophekad ion, Tri chogaster PectoråliS and T. trichopterus were found to feed more heavily on organic detritus in the Grass Area than in the l.leed Area. The availability and greater abundance o¡1 organic matter was probably the responsible factor. This demonstrates the role of organic matter as one of the most ímportant food sources for some freshwater fish. The-utilization of organic detritus as food by higher trophic level organísms such as fish represents a short cut in the energy pathway, w¡th increasêd efficiency of production of harvestable f ish flesh. The percent dístiibution of clay (less than 0.002 mm) was highest in the Grass Area (61.862) and significantly different from the Weed Area and the Open l,Iater Area. The intensity of decomposition of grasses,' could be the factor. The wind-protected character of the area woutd help the accumulation of clay. The high percent contribution of clay might reflect the high fertility of the soil sediment (Nees, 1949) because clay is i'ecognized as a powerful adsorbant of certain soluble nutrient elements and a governor of their distribution among impoundment organisms. The phosphorus content in the sediment was the highest (l l.99pp,:e ) in.'tÍhe Grass Area and'significantly different (p(0.01) from the Weed Area. Hephner (t966) found that phosphate was taken up by soil bacteria and regenerated by these'bacteria from organic matter in the mud. 0lsen (lger+) regarded bottom mud as a phosphate reservoir from which phosphate is transferred ¡nto the water when needed. The rate of -phosphate decrease and its final concen- trat¡on in water is a resultant of an equilîbrium between adsorptíon of l_61- phosphate from the vrater on the one hand, and its release back into water on the other (pomeroy, ì966 and Hephner 1966). A h¡gh total phosphorus content in the Grass Area may reflect high productivity. 2.2 Better feeding area The mean density of benthic organísms was higher in the Grass Area (l.zs n,/core) than in, the r,/eed Area (o.ag n/core). The water level fluctuation (F¡ll¡on, 196l) and the presence of rooted littoral vegetation (HcLachlan, 1969) such as Leersia hexandra, Hymenachne pseud.oiteru[ and cynodon dactylon may be responsible. Hynes (1961) found that 0ligochaeta increased on the exposed shore after a water level fluctuation in Lake Bala, England. clafl in (lgeg) reported that manipula- tion of water level has some effect on benthos in the Norwagian impoundments. The densi ties of invertebrates associated wi th Leersia hexandra (23.98 n/handful), rhe dominant plant species of the Grass Area (74.72y. or cover) r h/eFê higher than in Eichornia crassipes (Zl.OO n/hancl- ful), the dominant f loating plant of the l./eed Area (ZB.IOZ of cover). L. hexandrars life expectancy was much shorter than that of E. crassipes, though both appeared fairly sensitive to heat during the summer months. Therefore the benefit of L. hexandra as a habitat for fish foods is probably limited to only short life cycle and high reproductive rate organsisms. The organic detritus and planktonic feeders such as 0steochi lus hasseltii, Marulius chrysgphelgdion, Trichogaster pectoralis and T. trichopterus were found to feed more on organic detritus in the Grass Area than in the l'Jeed Area. I nsects were found ¡ n g reater numbers in the stomachs of i nsect i- vorous fish (Notopterus notopteru_s and Hystus vittatus) in the Grass Area than in the hleed Area. In the Grass Area small fish were found in large ,"1 L62 stomach quantities in contents of ,Ophicephalu.s- lucius, 0. s.triatus and .0. microPeìtes than !n the Weed Area. These phenomena indicate the high productivîty and avai labi I ity of fish foods in the Grass Area. Plant material such as grass leaves contributed Iarger quanti ties to the stomach contents of some herbivorous fish such as Puntius gonionotus, 'iiabiobarbus khulii and Osphronemus goraml in the Grass Area compared =--=:-:-=:---- to the l'/eed Area. This suggests the usefulness of establ ished grasses as fish food. :' :':: These differences in percent contribution of certain types of food to stomêch contents ,,'..,.:',,:,, the of the same f ish species caught f rom different areas , :.- . :. indicates the lack of special ization in feeding habits among freshwater fish (Hartluy, 1948 and Larglois 1954). Many invesrigators (R¡cker , 1937; Lachner, 1950 and Hrbacek, 1969) suggest that móst species of fish feed opportunistical ly but that such general izations must be made with reservat¡ons because selection of preferred foods has been described for atleastsomefishspecies.!arkin(l956)suggestedthattheabilityoffishes to change their diet by taking abundant foods, and to compensate for absence of their usual diet by taking some other food, may be an important ,,,,,,,,:,,'.,...¡,,, factor in regulating the abundance of various fish species. .,,,,"',,,' 2.3 Provide spawning g-round '"'.', , ' The effects of water level fluctuations on the reproduction of fish and the effectiveness of spawning in reservoirs is reviewed by several invest¡gators (sh¡eld, l95B; Runnstrom, 1960; Allen , l97o and Kuznetsov, ,,:¡,::.,..,r-..: l97l). Yakovleva (1969) stated thar rhe flucruations of water level ar a specific period could improve conditions and increase the breeding efficiency of the fish. Regier, Applegate and Ryder (1969) have pointed out that freshwater species generally spawn in areas which are at the early :.:.-::- ì. :, -:.1 successional stage. : ' :::.i' L63 InformatÌon concerning the effects of grass habitat on the reproduction of fish was obtained in this study. Such an investîgation is recommended and could provide useful information, particularly on the Anabantidae which buiìd nests aìong the emergent and floating vegetation as welI as on other fish which produce adhesive eggs. 2.\ Suitable biotope for short food chain fi sh species The total bîomass caught per giìì net set in Area B (ì09.69 g) was ,,. signif icantly greater (p( 0.0ì) than in Area C (33.94 or in Area D (26.63 s) 9). :, ¡... This indÎcates that the Grass Area is the most favourable biotope for fish fauna.r' The herù¡uorou, fish and insectivorours fish such as Puntius orphoides, Horulius chrysophekadion, Labiobarbus kuhì i i, Trichogaster pectoral is, Pristoìepis fasciatus and Anabas testudineus were more abundant in the Grass Area than in the Weed Area. Carnivorous fish such as 0phicephalus micropeìtes 0phicephalus striatus, Oxyleotris mamoratus, Ompox bimacuìatus and Waì la- gonia attu were more abundant in the l,Jeed Area than the Grass Area v¡hich may partly explain why prey species tend to congregate more heavily in the Grass Area. lt suggests selection of habitat by prey to protect or conceal ,,,,..,.. '.:J' themseìves from predators. : , 2.5 Source of nutrients ' As a consequence of flooding due to the monsoon rains many I E. crassipes stands drifted out of the reservoir. Therefore the fole of E. crassÎpes Ìn recyclîng nutrient élements was not comparabìe to t. hexandra which was covered by water, and then decomposed. Durîng the summer months the littoral grasses such as L. hexandra, Hymenachne pseudoiterum and Cynodol dacfylon had dried out, decomposed and mineraì ìzed. Floating vegetation such as E. crassipes, Salvïnia cucul lata and . L64 ::.: ,: : lsacnne globosa had drifted down to the open areas. \./hen the water rose again in the rainy season thè nutrients were reìeased back into the reservoir from the decomposed grasses. El I is (1942) recognized benefit to be derived from flooded marginal vegetation in Lake Murray, South Carol ina. Snieszko (lglll) described cultivated fish ponds in Poland in which the pìants were left as green manure contributing enormus amounts of fish food. 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