RESERVOlR FlSHERIES 1N SOUTH EAST ASIA : PAST, PK13SEN'14 AN11 FUTURE

C. H. Fernando Ilcpmtment of Biolog.~, Uniuersifg. of Wntwloo Waterloo, Onturio, Canuda

Abstract

Reservoirs are being constructd at :in accelerating pace in S*)uthEast Asia adding vastly to ancient and more recently built reservoir systems. At present ihc reservoir area for the region is 5.0 million hmn and the figure will itlcreasc to I 5 million hm2 before the turn of the ccntury. Natural lakes in South East Ash are few and some of theare atypical (flood lakes).

Fisheries it1 South East Asian reservoirs arc of very recent origin ;ind poorly developed. Fish yields :ire low in most areas. Indigenous fish species in South East Asia are mostly riverine. Introduced African cichlid fish (mainly T, mossambicaj have increased spectaculai~lgfish, yields in some areas. This can bc attributed to their more efficeint exploitation ofthe lacustrine h.shitat. It is suggested that introduction of lacustrine species is necessary if fish yields from reservoirs in South '\ktAsia :Ire to he increased to levels comparable to those founc! in tropical Africn.

Some adverse effects due directly or indirectly to the introduction of T. rnossambicn have been re.ported. Thesc include interference with culture in fishponcls and the spread of parasites.

The effect of introduced fish on fish yields in deep and up-country reservoirs has so far been small. It is suggested that deep water African cichlids be introduced into deep reservoirs and cold water tolerant species into reservoirs at high a1tit~1d.e~.It is suggested tlut iutroduc-d foreign lacustrjne fish may not take easily in areas like the Mekong where thc indigenous fish fallria is rich in species.

Cooperation between the different countries in South East Asia is desirable in developing reservoir fisheries. The shartng of expertise nntl hcilities will enable a more realistic and vlakle approach to research on and management of reservoir::. The potentla1 5 r ~ncreasedfish yields from South East Asian reservoirs is high. A rough estimate of rhc total reservoir yield hy the end of this century is 1.25 million tons. This fish yteld wrll also be avail:hle at: relat~velylou-=?st, on a sustainalde basis and in rc@ons where protein shortage is greatest.

CONTENTS

r. INTRODUCTIOK 2. RESERVOIRS : AREAS AND DIS'rRlBUTI( IN 3. THE FTSI-1 FAUNA 3.1 Tnd~gcnousfis'i fauna 3.2 Inti c ductlon OF foreign iisb speclcs Into reservoirs 3.3 'The irnpnct of tntlocluced fish species 4. PRESENT 1X5II PRODUCTION IN KESERVOlRS 5. FUTUKE 1WH INTR0DUCTIC)KS 6. BIOLOGICAI, STUDIES ON KESERVOIRS 7. hlANAGLMEN?' OF RESORVOIR FlSIIIXlES 8. ACKNC>WLEDGHMENNIS 9, RFTER13NCIiS I. INTRODUCTION

If the age of reservoirs is of any significance, South East Asia has the oldest. Reservoir building is suppwed to have c mrn~nc-dab?ut 4 ooo years apand they are being built at an accelerating pace in many parts of the world. This is true of S mth Elst Asia where the present reservoir area of about j million hm2 will increase to about 15 million hm3 by the turn of this century.

S nth Iht Asia is conspicuously poor in natural lakes compared to any other region except arid areas and S )uth Americ?. H~wever,both South America and Smth East Asia are rich in running waters; hence they possess a high potential f.)r reservoir construction.

Fisheries in reservoirs of any magnitude date back only a vcry short time 111 Sw~thEast Asia and the potential for fish production has been rcali .ed only to a very limited cxtent. The failure of indigenous fish species to give high yields In reservoirs is due to the lack of a lacustrine component among Snuth East Asian fishes. The plucky of natural lakes jn the region is certainly a major cause for this lack. Hqwever, in the last 20 years or so, reservoir fi jheries have assumed considerable importance in limited areas ltke , and this tend-ncy is spre-ding thrmghout the region. Marked increases in fish yields from reservoirs havc been noted in areas where Tilnpia spp. (mainly T. mssambica) have been introduced.

In the prcsent paper I shall discuss thc extent of reservoirs in South Jhst Asia in relation to other standing waters and the fish production from tkse reservoirs in the past, present and future. The composition of the indigenous fi;h fauna a~dthe role of intr?ducecl fish species on fish prod~ictionin reservoirs in S~thEast Asia will be evaluated. Rased on past experience, and the present situation, an attempt will be made to assess future fish yields.

The data I have used are drawn mainly from Sri Lanka, but I have included the available published and unpublished dxta from other parts of Smth East Asia. The reservoir fisheries of India have been ~~~~~~~~~d by J1lingran (1975). Fernando (1965, 1971, 1973) and Fernand,) and Indrasena (1969) ]lave deaIt in dctail with the reservoir fisheries of Srl Lanka. Achmad (1970) gives some data on an lnd~nesianreservoir. Yap (1974) gives fish prodwtion data for a Malaysian res-rvoir and Oopatham Pawaputonon (1976) gives dlta on fish production in Thai reservoirs. The earlier dm on reservoir fisheries in South East Asia have been summariz~dby Hickling (1961). Fernando and Furtado (1976) havc summarizzd the more recent data.

2. RESERVOIRS : AREAS AND DISTRIBUTION

In 195 t the reservoir area of S ~thEast Asia was estimated at less than I million hma (IPFC report quoted hy Dassart, 1974). The total area of standing watcr in the region was estimated in the same report as 3.2 million hm2. Th~sincluded rice fi-lds, estuaries, natural lakes, brackishwaters and fishponds. The present extent of reservoirs in the region is abmt 3.0 million hm2 (Table I). At the turn of the century this fi~ureis expected to Increase to 15 million hm"Tab1e I).

The total area of natural l-tk-s in the reg-ion amounts to only 1.8 million hm2. Hwwux, this fi ;ure in- clude~the f1oc.d 1, k~ of Camb :dia and I

Reservoirs are by no means evenly d;stributecl in Swth E%st Asia (Table I, Fig. I). The highest con- centration of ancient reservoirs is found. in Sri Lark? (Fig. 2). Recently constructed (mainly llrge) reservoirs are cmccntrated in Tnclia ard the Mekong region (FI~.I). Active reservoir construction at an accelerated pace is going on in Indonesia, S.:i Laaka, l.t~diaancl the Mckong region. Details of reservoir areas in the region are available for somc countries only. Jhingran (1975) has given a list of rnaj~~rlndlan reservoirs and their areas. Fernando (1973) has ;:iven a clerailec! list of all reservnirs over 300 hm in S -i Lwka. Data from 'I'hailand and Indmesia are given in Tables 2 and j. Fcrnandf) and Purt~do(1976) have m2.d.: estimates wherc p-)ssible of reservoir areas in th.e region ('Table I), but there is a gap in our knowledge of reservoir areas in Burma, Bangladesh, Victnam, Laos adCambodia. 3. THE FISH FAUNA 3.1 Indigenous fish fauna The tropics f-rm three widely separated, faunally distinct arcas, as far as freshwater fiih are c~nc-,rned. Lqwe McCmnell (196~)has reviewed this subject in detail and has discussed the re;ls-ms for this diIference and its implications. Of the three areas, only Africa has a lacustrine component in its fi;h fauna. The number of indigenou~freshwater fishes in each country of Smth East Asia is shown in Fig. 3. They vary from the very rich fauna of Thailand to the very poor fauna in Sri Lanka. Lowe McConnell(1969) gives fi:ur$s fxAfrican lakes, the Am2 :on Central America, Argentina and Smth Africa. S2me African lakes have over zoo species and the majw Africm rivers are rich in species too. The Amazon has over I ooo species. Althouph riverine fish are numerous, b9th S mth (and Central) America and Swth East Asia have few l~custrinefreshwater fi;hes, although Myers (1960) found a species flock of Cyprinidae in Lake Lanao, The Philippines.

Tropical Asian and Ssuth American freshwater fish faunas ate dominated. by Cyprinoidea and Characoidea respectively. Fishes of these families often breed only during high water following fl~ods.Lqwe McCmnell (1969) points out that the lacustrine cichlids of Africa breed throughout the year giving mqre stabl.: p3pu- lations of all siz-s. S-asonal fluctuations in food occur to a lesser extent in lacustrine than in riverine c3n- ditions. Plarktonivorous species can be expected in lacustrine conditions but hardly in riverine cmd'tions. The net result of these adqptations is that when reservoirs are built in Sonth East Asia the fish recruits available are orly poorly adapted for lakes.

The indigenous fi;hes that colonized reservoirs in Sri Lanlia include practically the whole spectrum of available species except torrent dwellers and some small stream fi;hes. A similar situation probably exists in other parts of South East Asia. The d~minantfish in the catch were the larger carps and large predltors. However, in no reservoir in the whole of S mth East Asia was the fi;h yield of indigenous species c3mparable to the high yields recorded in African reservoirs stocked with African cichlids (Hickling, 1961). Ulfortunately, we do not have much data from reservoirs where only irdigenous fi;hes were present in South East Asia. One of the reasons for this gap in data is certainly the very low yields which mad? fi;%ingunprofitable and not worth reporting. Where data are available, low valucs have been repxted f >r catches of indigenous species (Oopatham Pawaputonon, 1974; Jhingran, 1975; Fernando and Furtado, 1976). It is interesting to note in this cqnnexion that Holcilr (1970) found th.at the standing crop of fish in Cuban lakes was d3minated by two intrcduced North American lacustrine fi;hes. The "abviginal" fijh species which, were prcsent formed only a small percentage of the total fish catch, and in a backwater where only "aboriginal" species were present the stancling crop was much lower. Lin (19j3) noted that 80 percent of the catch in Haiti consisted of intro- duced T. m~ssamb;ca.

3.2 Introduction of foreign fish species into reservoirs Introduction of warm water focd fishes into South East Asian freshwaters was begun relatively recently, although carp and trout had earlier been intrcduced mainly into hilly regions. Schuster (1951) grave a list of fish sprcies introducd into tFe Indo Pacific region. Sreenivasan (1967) gave an exc-llcnt review of the status of Tilapia mossam5ica introductions in lndia and also mentioned the status of this fish introduced into other parts of the trcpics. Fcrnando (1965, 1971) gave a detailed list of species and the dates of their intro- duction into Sri Lanka. In all, I 5 specles had becn intrcduccd betwccn 1882 and 1969 into Sri Lanka freeh- waters. Four of these were African cichlids, two were from Incl.\ncsia, three from Europe (into upland reser- voirs) one from Thailand, one from Malaysia and two from mainland China.

Apart from trout and cqmmon carp, vcry little fistl introduction has been clone in South East Asia prior to 1940. Durinq the second world war an unknown fish (later ~hownto be Tilapia mossambica Peters) was Cound and distributed widely throuphout the Malaysian repion as a culture species. Thus T. mossombica made its entrance into South East Asia in an area almost devoid of rescrvoirs. It was later introduced into other parts of Smth East Asia with varying succcss. Chimits (19j j, 1957) has provided an excellent summary of Tilapia s~ccies,their c1llturc, bi~l3gy and intrr duction into countries b-th within aad, outside Africa. On the basis of the succ~ssof Tilapia mwambica in small low-cquntry reservoirs Fernard? (1965) suggested the addition of cornplemcntary spccics of Tilapia. This was d?ne latcr (Fcrnando, 1971). The example of Sri Lanka reser- voirs is particularly instructive. There are no natural lakes in Sii Lanka. I-Iowcver, of over ro ooo rescrvoirs some arc 3s old as I JOO years. Any stabilizltion of fishstxks could have occurred in this period to give the highcst yield possible. However, Ixforc the introduction of Tilapin mossambicr7 the fish yields from reservoirs wcre very low (Fernando, 1971).

From an cu.~minationof tlw a\ ailable data on indigenous freshwater fishfauna in South East Asia it is evident that "lacustrine" species are rare. Some riverine species may live in lacustrine conditions appxently s~~ccessfully.But fis'z yields under these conditions are low where only indigenous species arc involved. D~ta from Thai reservoirs show low standing crops (Table 1). Whether these figures will be any higher with stabili- nltion remains to be secn. Under the semi-lacustrine conditions of the flood lakes of Cambodia and Kali- mantan high fish yields of lndiganous species are recorded but ~t is not known whether any of the species from tflcsc regions can bc successfully acclimatizd to reservoirs.

3.3 The impact of introduced fish species A phenomenal incrcnse of fish yields in reservoirs following the introduction of fore~gnspecies has been noted in Srt Lmka. Fernando (I965, 1971, I 973), Fernando and Indrasena (I 969) and Fernando and Furtado (1976) have documented this very thoroughly. Spectacular increases in reservoir fish yields following the introc~uctionof Tilnpia 7nossatnbica have also been noted in Indonesia (Hickling, 1961; Fernand,) and Furtad,,, 1976). In lnclia wherc the introduction of this species has been restricted to certain areas only (Chauduri, I 964), large sized tilapiss have been noted in reservoirs by Sreenivasan (1967).

'rherc is consider~bkconfusion regarding the suitability or otherwise of foreign fish introductions in South East Asia. This applies especially to African cichliclae which are somehow considered more foreign. Incicleiltally, there are three species of cichlidae indigenous to South East Asia and one of them, Etroplus s~ratensis,(Bloch) is of some importance in reservoir fisheries. Anon. (195 j) advised apinst introducing T. mossambicu lxcausc of its aggressive nature. Chaucluri (1964) mentions that in India its ~ntroductionwas restricted to somc arcas only. Samehow th.c idea remains that South East Asia must bc self-sufficient in fish species for its own reservoirs.

When a nc\q reservoir is constructed the colonizing fish species are drawn from the rivers and stieams that dra~ninto it. In areas where natural lakes exist with an established lacustrine fish fauna, these species gradually establish themselves in the reservoir (Naidenow, 1972). Sometimes less valuable species (for food and spwt) attain numerical superiority and the addition of pred~torsdoes not seem to help much. Sin e theoret~calprinciples for hydrolriological forecasting are not yet elaborated, analogous deduction with the help of present knowlei1.ge of reservoir biology must be used (Naidenow, lot. cif.).

Whcn reservoirs are built in regions without a true indigenous lacustrine fid~fauna, their exploitation by the :~vailablttriverine species is only partially successful. One of the misleading factors in this situation is that some of the rivcrine species make good culture species in ponds, e.g., Catla catla (Hamilton), Cirrhina mripla (I-Iamiltm), Labeo rohita (Hamilton), Ptlntius javanicus (Bleeker), and various carps throughout the region. But in reservoirs these species do not give high fish yiclcis.

Tilapia mossambica has becn introclucecl most 11 ~delyin South Ilast Asia. It is founcl, to "runt" in ponds. Srecnivasan (1967) found tkis to be sr, 111 lnclia. However, in reservoirs it does not runt (lk-nando 1965,1971) 1973). The coeff~cicntof condition K and the mean size of T. ~ossa~bicnin Srl Lanka are given in Table 4, which shows that in reservoirs it is not stunted and has a high K compared to fis'ip mds and a szline lagoon. Crowding ;ml hod nvailability seem to be the factors determining K, sincc Canagaratnarn (1966) found that Tilapia mxrsambica grows faster in salinc than in fresh waters.

In Sri Lznka of the I;? warm water foreiyn species ititrtduced only Tilapir2 m9ssambica has had a major impact 1:n fish yields in reservoir:;. Table j gives the fish yielils from resrrvoirs in some South East Asian countries. Sri Lnnka has thc highest yield... Fish, catches from different types of reservoirs in Sri Lanka (Table 6) show a wictc rangc. 'I'hc species composition shcws a preponderance of T. mo.rsam5ica in the catches.. Tdi- genous species include Efroplus sumtensis, an indigenoue estuarine cichlid introduced into reservoirs; Lgbeo dusszderi (Val.); Pwtius spp.; and predators likc WulIago athi (B1,)ch and Schneider). The goramy, Osphro- nems goramy (l~ccped?),a riverine Indonesian specics appears in the catches but hardly any common carp were caught despite the relcase of millions of fry into reservoirs (Table 7). It is intcrestirx; to note that within a small country like Sri Lanka considerable differences exist in the species composition of fish catches in reser- voirs, e.g., no Wallago or Labeo are caught in southern reservoirs (Table 7). It is noteworthy, though, that indi- qenous fish species have not been eliminated by T. mossambica. The exploitation of indigenous fish species in kservoirs has become feasible only because of the large standing crop of Tilapia. Incidentally, Alfred (1961) states that of the 70 species of indigenous freshwater fishes recorded in Singapore, only 32 are now found. This is dde to the effect of high human densities. Mani (1974) and Fernando (1975) have pointcd out that the Indian freshwater fauna has been reduced by human interference. Apart from African cichlids (mainly T. mossambica) other fish species have been intruduced in S~~uthEast Asian reservoirs. These belong to three categories: (i) riverine species, e.g., Labeo spp., Catla wtla, Puntius Jauanicw and. Ospbronemus goramy; (ii) marsh and local estuarine species, e.g., Tricbogaste~pectoralis (Regan) and Etropltls swatensis and (iji) domesticated and semi-domesticated species used in fish culture, c.g., Cjprinus carpio L. and Chinese carps. The so-called Indian carps have increased fish yields in Southern Indian rcservoirs. Etropbs swatensis and Osphronamus goramy are caught in some quantity in Sri Lanka. Although some indi- genous marsh. dwellers seem to thrive in the shallow littoral of reservoirs, their overall cmtribution to the fish catch is generally low. Hardly any impact has been made on reservoir fi;heries by domesticated or semi- domesticated fish.

Some adverse effects have been reported as a result of fish introductions to reservoirs. Fernando and Furtado (1963) and Fernando and I-Ienek (1973) found that helminth and copepod parasites had been intro- duced into Sri Lanka with introduced fish species and these parasites now infested indigenous fish species. Sr:enivasan (1967) reported that the introduction of Tilapia ~;:ossaml?icahad had adversr: effects on the pond culture of the milkfish Cbanos chanos and the common carp Cyprintls carpio. Zaret (1974) reported that the introduction of a new predator caused a serious depression in the fish population in a Central American lake.

4. PRESENT FISH PRODUCTION IN RESERVOIRS Taken as a whole, reservoirs in outh East Asia have a low fish yield. Only about 60 ooo metric tons are harvested from over 3.0 million hm' (Fernando and Furtado, 1976). This gives an average of 20 kg hm-' year-l. The range of fish yields is 0-600 kg hm-a year-l (excluding some very eutrophic, shallow lakes). Table g gives the fish yields in some South East Asian countries.

Fernando and Furtado (1976) have given the fish yields from a wide range of reservoirs throughout South East Asia. In the present paper, I have added data from Thailand (Table 3) and southern reservoirs in Sri Lanka (Table 6). All the reservoirs having high yields are (a) shallow and (b) stocked with African lacustrine cichlidae (mainly T. ~ossambica).India and Thailand, which between them have about 75 percent of the total reservoir area in South East Asia, have low fish yields at present. Sri Lanka has high yields and Malaysia and Indonesia have few reservoirs. Fish yield in some Indonesian reservoirs is, however, quite high. Deep reser- voirs and upland reservoirs have low to negligible fish yields in general. Perhaps this can be r-medied to some extent with deep water cichlidae from the African great lakes and low temperature-tolerant Tilapia species like T. sparmanni (Castelnau) and T. galilaea (Ardeti).

5. FUTURE FISH INTRODUCTIONS The questions that must be raised are: (i) whether any more fistl introductions should be made into reser- voirs in South East Asia and (ii) if introductions are to be made, what selection of fish is mpst suitable. From the experience of the past 3 g years it is evident that indigenous fis'? do not give high yields in reservoirs under any circumstances in South East Asia. It is necessary, therefore, to introduce lacustrine fijh if exploitation of reservoirs for fisheries is to be intensified.

Tilapia mossambica has been introduced widely into Sxth East Asian reservoirs. This fish has raised fish yields (often spectacularly) in shallow reservoirs. However, it has not had such a marked impact on the fish yields in deep reservoirs. Caulton and Hill (1973) have shown that T. mossam5ica is unable to adzpt to d2pths of over 13 m. Fernando (196~)proposed the introduction of deep water Tilapias into deep, South East Asian reservoirs and complementary species of Tilapia into shallow reservoirs. Based on the recqmmen- dations of Fernando (loc. cit.) three complementary species were introduced into Sri Lanka r-servoirs (Fer- nand?, 1971). Eccles (1975) has proposed the introduction of cichlids from the African great lak-s into large (presumably deep) tropical reservoirs. Fernando (1971) also proposed the introduction of T. galilaea, a deep water Tilapia ard T. sparmanni, a cold water-tolerant species for deep up-country reservoirs. An exc-llent accwnt ef the cichlidae of the African great lakes is given by Fryer and Iles (1972). Lacustrine cichlidae of Africa offer a wide range of siz:, food preference and breeding behaviour.

W'iile the introduction of Tilapia spp. has taken place in some areas of Smth East Asia, they have not b-en successful in others, e.g., Ling (135 3) states that they were eliminated from open waters in Thailxn?. It will not be surprising if there is great difficulty in establishing foreign species in reservoirs in thq Mekmg region due to the vcry l~rgenumber of indigenous species and the semi-lacustrine cnnditions in the Grand LIC. This area ~rnbablyhas fis'7. species adapted to lacustrine conditions found in reservoirs. Predxtqr pr-ssure has eliminated T.mmambica in other parts of the world, e.g., in Guyana sugarcane fields (Lowe McCxmell, 1969). It is important that a careful study be made of th.e impact of the present introduction before future intro. ductions are undertaka on a large scale. However, the air must be cleared of suspicions as regards intro- duction of foreixn species. If introductions are decided against, in any particular area, this should be based on careful scientlic study and evaluation.

6. BIOLOGICAL STUDIES ON RESERVOIRS The extent of biological studies on reservoirs at a global level can be assessed by the research in this fi~ld over the last 30 years or so. Although a field of recent scient;fic endeavour, three international symp3sia have already been held on reservoirs. (Lowe McConnell, 1966; Obeng, 1963 and Aclrermann et al., 1973). In the U.S.A. two symposia have be-n devoted to reservoirs (American F~sheriesSociety, 1967; Hall, 1971). The Soviet Union has led the world in reservoir construction and research. The earlier work has bzen reviewed by Z'xadin and Gerd (1961). Frey (1967) gave a summary of reservoir research in the Soviet Union, andBaranov ef al. (1973) show the possibilities for enhancement of yields by fertilization and the intrxiuction of inverte- bratps. The Irldian Cwncil for Agricultural research orgarized a symposium on reservoirs in 1969 (Anon., 1969) at which over 10 Papers were presented. Reservoir fisheries in Sri Lanka have been repxted on by Fernand? (1965, 1971, 1973), Fernando and Indrasena (1969) and South East Asian reservoir fijheries have b-en summariz-d by Fcrnando and Furtado (1376). Wmg and Ku (1970) refer to three papers on reservoir biol3gy in mairland China. This list is probably incomplete. Although S~thEast Asia has 2 sizabls reser- voir area, very little is known about their biology and despite some excellent work in India (see Jhingran, 1975 for summary), we still know practically nothing of their znoplankton and benthos. Outside the South Exst Asia region there is a monograph on an African reservoir Lake Kariba, by Balm and Coche (1974) besides a cmsiderable amount of work on the biology and fisheries of African reservoirs.

7. MANAGEMENT OF RESERVOIR FISHERIES It is imnmant to the development and management of reservoir fisheries in South East Asia that a co- operative cffxt be made to pool the information avaihble for the whole region. We need more reliable and c .mplete statistics of reservoir areas, fish yields, species composition and seasonality of fijh catches and the effects of introduced species. This will enable better planning and management of reservoir fis5eries.

An attempt should be made to standardize data from this region. For example, fi;h yields have b-en calculated on the basis of half the total (full supply) area of a reservoir by Srzenivasan (1969). F-rnando (1971, 1973) h.~,however, used full supply levels for areas in calculating fijh yields. Reservoir levels do fluctuate considerably as shown for two Sri Lanka reservoirs by Fernando (1967, 1971).

Although the problems of reservoir fisheries in S?uth East Asia are unique in some respects, the extensive results frnm research and management in other parts of the world can help in formulating research and mmage- mznt pr9grammes for S~thEast Asian reservoirs. This literature, which has been reviewed earlicr in this p-tper, mmbined with other work already done or being done in South East Asia, can form a solid base for planning and further studies.

8. ACKNOWLEDGEMENTS I wish to thank Mr. S. Achmad, Director, Lake Fish Station, Jstiluhur, Indonesia; Mr. S. Varilrul, Fisheries D-partm-nt, Bangkok, Thailand and Mr. M. T. T. Fernando, Deoartment of Fisherks, Ud~walaweStatim, S:i Lanka, for data on fish catches and reservoir areas. Dr. Juraj Holcik, Bratislava, Czechoslovalria; Dr. Jose Purtado, University of Malaya, Kuala Lumpur, Malaysia, and Dr. V. G. Jhingrar, am1 the scientific staff at the Central Inland Fisheries institute, Barraclipore, India, offered their critical comments on my views on reservoir fisheries. Part of the v~ ork embodied in hrs paper was carried out during the tenure of a research Associateship awarded by the Tnternational Development Research Centre, Ottawa, Canada. 9, REFERENCES Achmad, S., Some notes on fisheries of lake Djunad:~Djatiluh-ur. 1970 Rep. Inhnd Fish. .Kes. Sfn. l?jotJdvtr, (2) : 12 13. -!ckermann, W. (:. ef nl. (I'ids.), Man-made lakes: their problenis and environmental effects. 1973 Gtopbys. hfoiatlqqr., (I 7) : 847 17. .\lfred, E. R., The Singapore freshwater fishes. .Ala/qy. Not. J., J J : I - 13 1961 .American Fislzcries Socicty, Southern Division, Reservoir Committee, Proceedings of the reservoir fishery. 1967 resources symposium. .Athens, Georgia, Southern Division, American Fisheries Society, 569 p.

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TABLE 1 AREAS ( hmz x 106) OF SOME TYPES OF INLAND WATERS PRODUCING FISH IN SOUTH EAST ASIA (MODIFIED FROM FERNANDO AND FURTADO, 1976)

- -- Reservoirs Natural lake.~ Country T~~~~ - Present Future Ricefields ------. .- - -. . - - -.- . Bangladesh ...... N.A._.I N.A. 10.000 N.A.9 Burma ...... 0.010 0-150 5.000 0.050 FP India ...... 1.3 5.000 40.00 0.2y Indonesia ...... 0.050 0.500 8.000 1.00 NL 0.100 FP Cambodia ...... 0.080 2.000 2.000 0.400 DP Laos ...... 0.050 5.000 0.700 N.A. Malaysia: Malaya ...... 0.020 0.150 0.50 0.008 FS Sabah ...... N.A.21 N.A. 0.050 N.A. Sarawak ...... N.A.:/ N.A. 0.120 0.010 FP 3.187 FS 0.006 FL The Philippines ... N.A.r/ N.A.J 'N. 4.51 0.100 FP & NL Singapore ...... 0.0002 0.0003 Ni 1 Nil Sri Lanka ...... 0.125 0.250 0.600 0.020 FP Thailand ...... 1.2 2.0 6.700 N.A...... - -- Total ...... 3 .O 15.0 70.0 NL: FP: 1.850 (Approx)...... FS: 3.2 N.A = No data available :/ = Negligible = Considerable FP = Flood plain NL = Natural lakes FS = Freshwater swamps 5,' = High olevation lakes in [ndia and Pakistan TABLE 2 DATA ON AREA AND MAXIMUM DEPTH OF SOME INDONESIAN LAKES AND RESERVOIRS (FIGURES SUPPLBD BY S . ACHMAD. DIRECTOR. FISHERIES STATION. JATIL~UR.INDONESIA)

Lak~/Reservoir Area (hm9 Depth (m) ...... - ...... SUMATRA Toba ...... Kanau ...... Singkarak ... Maniniau ... Diatas ...... JAVA ?/ Jatiluhur ... a! Cigombong ... .I Ciburuy ... Darma ...... :I Rawa Pening ... .ai Rawa Jombor ... Telaga Ngebel ... Ranu Klakah ... Ranu Pakis ... Ranu Klindungan Ranu Bedali ... / Rawa Jahung-Mlangi Telaga Pasir ...... a/ Karangkates ... .,! Selorejo ...... Waduk Bumder ... Wadtrk Bureng ... Waduk Prijetan Waduk Kalen ... Waduk Paeal ... SULAWESI Tempe ...... Towuti ...... Matana ... Manalona ... Lindu ...... Poso ...... ! Rawa Aopa ... . Limboto ... KA'LIMANTAN Luar ...... Sekentu t ... Sum bu ... Arawan ...... Termabas ... Siawan ... Panggang ... LESSER SUNDA ISLANDS Rawa Taliwang ...... Bratan ...... Batur ...... 1 590 88 I! Reservoir No. Region Vnme Water Swface Standing Crop:/ Annual Crop.$/ Area kg hm-2 kg hm-2 ( 103 hme) year-' Northeast 1 Lam Praperng 2 'Lam Takong 3 Lam Poa 4 Oon 5 Sirinthorn 6 Ubolratana 7 Nong Han 8 .Kaeng Lurn Chan Nwtb 9 :Bhumipol 10 Sirikit 11 Kwan Phayao 12 Chew Lom Central 13 Kaeng Kachan 14 Bung Borapet - fTotaT) 1 133.7 (Average) 21 (Average) 11 i6

-a/ From Rotenone Sampling From fish landing statistics

TABLE 4 THE STATUS OF 'MLAPIA MOSSAMBICA IN SOME HABITATS IN SRI LANKA (FROM FERNANDO, 1971)

Habitat Fish ------Max. Area Description Mean Mean Coe#?cient Fish catch Namc of Habitat Depth (hmz) Length Weight of condition (kg hm-- (4 F.S. L. (4 (d (k *) year-1) - 6.1 60.75 Brackish highly fertilized 15.9 93 2.25 2 244 18.3 11 950 Brackish 20.4 144 1.70 (28-56) Fish ponds 1.22 0.10 Freshwater 17.6 90 1.79 1 795 Karapola villu 9.15 810 Freshwater marsh, 26.8 443 2.10 84 connected to river Tabbowa Tank 9.15 461.7 Freahwater lake (shallow) 24.8 338 1.95 (56-84) 12.2 2 264 Freshwater lake 28.4 443 1.88 180 (34.2 in 1957) Minncriya Tank 18.3 2 552 Freshwater lake (deep) 29.4 598 2.00 118 Kandalama Tank 21.35 984.2 Freshwater lake (deep) 31.4 651 2.02 (5684) Senanayake Samudra 45.75 77 939 Freahwater lake (very deep) - - 400 -- 9 All samples taken in 1964-65 *K = W x 103 W - weight in grammes Fish production values for 1963 L5 L - length in millimetres 'P@ures within brackets are rough estimates TABLE 5 MSH PRODUCTZON (YIELD) FROM RE(SERVOIRS IN SOME 59, ASIAN courvrms. FIGURES ARE.-. BASED ON FULL SUPPLY LEVEL AS TOTAL AREA. ACTUAL YIELDS SHOULD THEREFO* BE SOMEWHAT HIGHER Count~v Reservoir Area Runne CYieidl Mean (Yield) Source (106 hm2) , (kg h&-fyecrr-1) (kg hm-2 ~.earll) ...... - ...... -> --., -. . ,.... - ...... , ...... -. - -- . !!,indid ...... I .3 0 - 250 6--.6 J hingran , 1975 Sri Lanka ...... 0.125 0 - 610 100 %mando, 1973 Indonesia ...... 0.040 0 -. 600 About 50 Achmad pers. comrn. b! Thailand ...... 1.2 32 -- 9w 20 Oopathan~ .I4 Kescrvoira Pawaputonon, 1974 C! W. Malaysia ... 0.020 0 - 90 20 Fernando and Furtado, 1976 South East Asia ... 3 .0 0 -- 600 20 Fernando and Furtado, 1976 African cichlids very restricted b/ African cichlids not established c/ Standing crops

TABLE 6 PISH CATCHES IN DIFFERENT TYPES OF LAKES CN SRI LANKA IMODIHED FROM F~RNANDO.1~31 Standitig Crops~/Dry Wt. .... R~wrv(rir Area War. Dep//r Total Catch Catch Years (s) Plank ton Benthos (hmz) C~R) (kg hm-2 (kg hm-2) (kg hm-9 yew-1) .... - -...... Large shallow lowcountry reservom : Parakrama Samudra ... Minneriya Tank ... Kantalai Tank ... Giants Tank ...... Large deep low-country : reservoirs Senanayake Samudra ... 497 060 :20 1961--64 Nalanda Reservoir ... nil nil 1960 ----70 Upcountry reservoirs : . Castlereagh reservolr.. . nil nil 1960----70 Small low-country reservoirs : Dalukanawewa ... Beira Lake:/ ,. . Moragaswewa ... Thimbrirgaswewa ... Stnail up-country reservoirs : Gregory's Lake ... cpch fishing is negligible 1900- 70 Kande Ela Tank ... no fishing 1960--70 Southern reservoirs : Muruthuwelawewa ... Wdukiriwelawcwa ... Udawalawe Reservoir ... Kidlyagamawewa ... Badagiriyawewa ... Chandri kawcwa ... \I Dat:i from Mendis (1964, 1965) bl Highly eutrophic :I Probably highly eutrophic North Central Province Parakrama Samudra ...... Minaeriya Tank ...... Karapala Villu ...... Pastern Province Scnanayake Samudra ...... Southern Province .Muruthawela Tank ...... Ridiyagama Tank ... ,.. Badagiriya Tank Udirkirwewa ...... JavS Province Chandrikawewa ...... Javd-Sabaragamuwaprovinces Udawalawe lkservoir ...... O- O- miles

Figure 2: Reservoirs in Sri Lanka.showing high density mainly of ancient reservoirs (after Fernando, 197f). - .- - Figure 3: Indigenous fish species in South East Asia. Data from Alfred (1961), Dussart, (1974); Fernando (1971), Inger and Chin (1962), Jhingran (1975) and Smith (1945). Numters within braekets are only very rough estimates. Singapore has lost 38 indigenous freshwater species durmg thls century according to Alfred (1961).