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Home , Haplochromis, Nile perch

The biology and distribution of spp in the Nyanza Gulf prior to the total invasion of the Gulf of perch, niloticus (L)

Item Type Proceedings Paper

Authors Mwalo, O.M.

Citation Okemwa, E; Wakwabi, E.O.; Getabu, A (Ed.) Proceedings of the Second EEC Regional Seminar on Recent Trends of Research on Fisheries, NAIROBI : ICIPE SCIENCE, p. 73-83

Publisher ICIPE SCIENCE

Download date 24/09/2021 11:43:30

Link to Item http://hdl.handle.net/1834/1158 The Biology and Distribution of Haplochromis spp in the Nyanza Gulf Prior to the Total Invasion of the Gulf by , Lates niloticus (L)

0.Mainga Mwalo National Council for Science and Technology P. 0. Box 30623, NAIROBI

Abstract

The work reported was conducted during the watershed period of 1976 when Nile perch (Lates niloticus) started to replace Haplochromis spp. in dominance in the Nyanza Gulf. Seventy four "groups" of Haplochromis flock obtained from a stock assessment survey of that year were used in the study. The length of examined varied between 57 and 237mm total length, and between 1 and 1829 wet weight, with means of 101.05mm and 18.539 respectively. Frequency distribution curves for both sexes were unimodal with a maximum between 70 and 130mm. The t- test showed that the two sexes came from the same population. Clutch size per fish ,(mean weight 25.39. and mean total length 106.7mm) was 78 eggs. The minimum size at maturity was 89mm for males and 93mm forfemales. Living condition coefficient was highest at developing stages. Sex ratio calculations per "group" were found illogical as most "groups" were exclusively monosexual. Most of the "groups"fedon phytoplankton (41%), others on Molluscs (12"/0), fish material (12%), larvae (9%), adult (8%), macrophytic detritus including sand grains (7%) and (4%). Feedingcompetition waslowest among thegrazersonthe abundant phytoplankton and highest among the adult aquatic insect eaters. Nematode parasitic infestation was common among female fish. The Mann-Whitney non-parametrictest showed no significant difference on the conditions of the infested with parasites and those not infested. Haplochromis spp. were collected in all the hauls and usually in greatest concentrations from a depth of 4m through to 49m. Over 80% of the 74 "groups" were represented in the 4-9m depth interval, 59% in the 10-1 9m depth interval, 68% in the 20-29m depth interval, 30% in the 30-49m depth interval and only about 10% of the groups were represented in the deepest 50-69m depth interval Introduction work, therefore, can hardly be underestimated. From 1976 onwards Nile perch (L. Before the collapse of the East African niloticus) production in Nyanza Gulf Community, the introduction of a trawler increased dramatically. Over the same fishery based on the abundant period Haplochromis spp. catches have Haplochromis stock was envisaged. But fallen drastically. The comparative figures before the introduction, it was felt necessary for the two fishes have been: Nile perch to conduct a survey of the fishery with a (percentage total catch contribution) has view to answering certain pertinent risen from a mere 0.5% in 1976 to 67.7% questions such as: in 1983 and to49% in 1988; Haplochromis spp. contribution on the other hand has 1. What feeding groups of fallen from 34% in 1976 to 0% between Haplochromis spp would contribute 1984and 1986and toamere 1.1%in1988 to the commercial catch? (Achieng, 1990). Considering that in the 2. What would be the depth distribution 1970s Haplochromis spp. were estimated patterns of the exploitable to constitute almost 80% of all demersal Haplochromine groups? fish biomass in Lake Victoria, this drastic 3. What is the general ecology and replacement by Nile perch from such a biology of the Haplochromis spp. in dominant position is indeed an ecological the lake? destabilization of the highest magnitude. Achieng (op.cit) has commented that Nile The present work was mounted by Perch has "transformed the industry EAFFRO to investigate these questions. and the species composition of the fish fauna in the lake more than any other Materials and Methods phenomenon this century." Apart from earlier studies conducted Stock assessment trawling was by the defunct EAFFRO on the natural conducted in the fourth quarter of 1976. history of Haplochromis species, there is Sixty three one-half hour trawls were very little work reported on their biology accomplished utilizing the EAFFRO and distribution in the Nyanza Gulf. The research vessel "MV Cormorant". The present study is probably the only major vessel, which was fully rigged for stem work conducted in Nyanza Gulf, with trawling, had a 125HP Caterpillar engine specific reference to the distribution and with a maximum speed of 8 knots. It had biology of Haplochromis spp at the crucial modem navigational and echo sounding period, when the species still dominated equipment and a 2-ton mechanical winch. the catches and Nile perch proliferation Though trawling was concentrated mainly was just beginning. Since then, and with in the Nyanza Gulf, the operation also having been replaced in covered the open deeper Kenya waters abundance by the Nile perch. tHe near the borders withTanzania and Uganda opportunity to get a similar study material (Fig. 1). All trawlable depths in these areas of Haplochrominesin such abundance and were covered. Trawling speed was large diversity might never occur again. maintained at 2.5 knots. The historical importance of the present The various fish species (or genera) Fig. 1. Lake Victoria (Kenya) showing the areas trawled in 1976 caught at the various depths were sorted closer biological study, much of it in out and thcir numbers (whcre possible) preserved condition. and wet weights taken. Samples of The fishes were sexed and their general Haplochromis spp. were taken from all morphometric data (length and weight) dcpths for depth distribution analysis. By taken. For maturity stages, De Silver's the end of the trawling operation a total (1973) scale was adopted with the following samplc of about 7,000 Haplochromis fishes modifications: stage 1 to stage IIA was weighing 85kg. had been collected and called "Immature", IIB to I11 was called "identified" into 74 "groups", which were "Developing". IV to V was called tentatively called "species" due to the "Mature", and VI to VI-I1 was called known taxonomic difficulties involved "Spent". Ovaries in the "Mature" stages (Benda and Mainga, 1977). The were preserved in Gilson's fluid. Later the "identification" was based on broad hardened eggs were separated, dried in an morphological characters such as body oven and removed for counting to shape and size, colour and prominent determine fecundity. Fecundity was markings such as bands, spots orbars. Out defined as the number of maturing eggs of this large sample, a sub-sample of about per unit weight or length of fish found in 605 fish from all the groups were taken for the ovary just prior to spawning (Banegal, 1967). For living condition, the method of The pressure of competition for a Nikolsky (1963) was adopted with slight common food item was studied using modification: the whole alimentary tract Harlley's (1948) formula: from just below the pharynx to the vent Intensity of was removed. The assessory structures Competition = Other food items x 100 such as the liver, gal1 bladder and pancreas Major food preference + were discarded to avoid obstruction when other food items analysingthe proportion of fat cover on the gut. The fat coier was estimated on an The presence or absence of internal increasing scale from 0 to5 units to indicate parasites were noted, and their effects on the "living condition coefficient". the well being of the fish were investigated Stomach contents were studied under a by comparing the living conditions of field microscope and the food items were parasitized fish with those not parasitized. grouped into seven categories based on an earlierpreliminary trial: (1) Phytoplankton Results (2) Zooplankton (3) Adult insects (4) Insect 3 .I Morphometrics larvae (5) Molluscs (6) Macrophytes and/ or Detritus including sand grains (7) Fish The lengths of605 Haplochromisvaried material. between 57mm and 237mm total length while weight ranged from lg to 182g. The length-frequency distributions (Fig. 2) for

Males -N = 281 X = 101.05 mm Range 58-202 mm

L 4 ~d- Females 1

III Range = 57-237 mm I

Total length sizes (mm)

Fig. 2. Size frequency distribuhon of all Haplochromis spp both sexes indicated a greater number of 3.3 Size of Maturity fish occurred between 70mm and 130mm. The average minimum length at which 3.2 Fecundity maturation occurs was calculated using Burd's (1962) method for North Sea Data on egg production were obtained herring. The resultant graph (Fig. 5) for from a random sample of 15 out of 54 both sexes showed the minimum size at mature female fish; theirmean weight was maturity to be 89mm formales and 93mm 25.3g and mean length was 106.17mm. for females. Table 1 shows the sex The mean egg count was 84 eggs per fish. distribution of the Haplochromk groups Fig.3 gives the relationship of fecundity to studied. body wcight of the fish examined. The relationship was linear as represented by 3.4 Living Condition the following equation: F = 20.8 + 2.25 W, r = 0.794 Results of fat deposition in the The total Length-body wcight relationship mesenteries surrounding the gut showed of fecund fish (Fig. 4) was curvilinear as that most of the groups had low fat content follows: at the time of capture (Fig. 6). The highest a = 1.280 x fat content was recorded for fish in the b = 3.542 "de.~eloping"stages, followed by those in c = 0.90

Body weight (gm)

Fig. 3. Relationship between fecundity and body weight in Haplochromis sp. Total length (mrn)

Fig. 4. Relationship between body weight and total length in Haplochromis the "mature" stages. Fish in "spent" and material and detritus and 4% fed on "immature" stages had the lowest fat zooplankton (Table 2). content. The Hartley 's feeding competition ratio showed that competition was least among 3.5 Feeding Habits the phytoplankton feeders and highest among the insect eaters. It was also high The Haplochromis groups studied fed for the detrital and macrophytic feeders on 7 broad groups of food items: and moderate for zooplankton and insect phytoplankton (principally the filamentous larval feeders. Fish eaters had little and the gelatinous colonial types of algae), competition for food. zooplankton (mainly ), molluscs (mainly gastropods), adult insects 3.6 Parasitic Infestation (terrestrial and aquatic types), insect larvae. macrophytic plant material and detritus Adults and larval nematode cysts, (including sand grains) and fish (larval and tentatively identified as those belonging to adult stages). On the basis of occurrence, Eustrongylidae spp. (Papema. 1973). were phytoplankton made up the greatest found in 23 female and 17 male fish. The percentage of their diets (4 1% of the fish). white cystsofthe larvae and adult parasites About 12% fed on molluscs, another 12% were found in the tissues surrounding the on fish material (especially small viscera and the gonads. It was observed fishes); 9% fed on insect larvae; 8% on that gonadal infestation occasionally adult insects, 7% on macrophytic plant resulted in degeneration of the organs. especially the ovaries.

Table 1: Sex distribution of Haplochromis groups

Monosex group Group of Single specimen Total mixed sexes groups groups

Male Female Male & Female Male Female

Immature Developing 80- Females 46% Females 68% Males 54% Males 32% 60 -

40 - -f.- 20- 0 I 9t 0. z5 So- Spent Mature Females 37% Females 33% 60 - Males 63% Males 67% 40 -

20 -

Living condition (Fat Units)

Fig. 6. Fat content frequency distribution based on maturity stages

Table 2: Percentage occurrence and 'Competition Ration" of the food consumed by Haplochromis spp

~h~to~lanktonZoo- Adult Insect Molluscs Detritus Fish Insufficient plankton Insects Larvae andlor data or Material empty Macrophy tes stomach

Major fwd Preference (a) 14 4 8 9 12 7 12 7

Major fwd item (b) 8 4 20 9 7 14 5 35 bx100 a+b 9+b 16.4 50.0 71.4 50.0 36.8 66.7 29.4 The condition coefficicnls (Tat units) scason than females. Thc tcndcncy is calculated separately for non-parasitized seemingly shared with another Cichlid, fish against parasitized fish were 1.33 and heTilapia (Otte, 1986). 0.97 rcspectivcly. The Mann- Wlutncy non- The study on sex ratio is interesting paramelric test (Zar, 1974) showed no because, of the 74 groups, the majority of sibmilicantdiffc.rence(Z= 1.2888)belween the groups were either exclusivcly femalcs the Lwo caregorics of fish. (46%) or males (30%). This led us to conclude that sexual rather than taxonomic morphological characteristics was the major underlying factor in our original groupings. In [his regard thcreforc, female A [oral of 8.7 tons of fish were landed. Hr7plocllrornis tended to show stronger comprising various species (or genera) bul sexual dimorphism than males, especially predominant1 y Hrll11ochronli.s spp. Bagrus as the!, approach maturity. This probably t1oc:trinc. Clrzrias rt~ossamhicr~s. ensured successTul pairing during brecding Proroprencs c~crhiopiclrsand varied Tram season Anolher possible conclusion to be as high as 344 kgir ol'fkisengere Channel drawn I'rom rhe sex ratio study is that if we to as low as 34kg./tlr in lhe Nyanza Gulf. assume that the exclusive female groups The calches were dominated by ([he majority) rcpresenled distincl Haploc,llrotnis spp. which on average individual species (which would pair with accounled li~r67.20/0 of toral weight. the exclusive male groups) then wc Hnploctlrottlis spp. were collected in all probably had aboul 34 Huplochrorni.s hauls and usually ill greatest concenlralions speciesinoursarnples. Althoughone would Lroni a deplli oS4m through ro 49m. Over argue that this is a far-felched cry from thc SOYO col'the 74 Hnl)lochrotrlis groups werc over 1OOspccies ofHaplochron~isreported, represenred in the 4-9m dep~liin~erval. nonerheless it does prove that quile a 59% between 1&19in, 6870 between 20- numberofH~ll)loclrrornisspecies did exist 29m, about 30% in the 3049m depth in the lake. interval and only aboul 10% of [he groups In Ha~~lochrornis,as in olhcr fishes wcre represented in he deepest parrs of (e.g. Okera, 1974,Gupla, 1975)deposition 5(?-69m (Fig. 7). of fa1 as the I'isli maturcs seems to be an investment for Lhe stressful period of' Discussion brceding. Encrgy scored in Tat is utilized duringhiscritical period, and at theend of Thc majorily of Hczplochrotnis spp. the period thc spenl fish has little Tat lelt in caught in the areas trawled were berwcen thc body. small lo medium in size. However, lishes Hal11ochronri.s Teeds on a broad range caught in the deeper waters tendcd lo be of food items. This Cdclor, more than any bigger in size. In facl the biggesl lishes other, may have conlributed to the wcre caught in the deepest parls of the successful proliferation of he lish in the lake. lakes where i~ is round, as it ensures The observalion made th;~tthc minimum maximum utilizatioii ofhe food resources size at maturity formales (89mm) is bigger (Fryer, 1969; Dunn, 1975). In lhe Nyanza than lhose of females (93nim) seems to Gull', competition Tor rood did not seem lo indicate hat males mature earlier in the he a major problem, especialiy among Lhe Depth intervals (M)

Fig 7. Distribution and percentage contribution of all Haplochromis groups present at each depth ~nterval phytoplankton fceders (41 O/c of thc fishcs) bctwccn Lhc fish and its parasitc sccms to as phyloplankton seems to be plentiful. havc been struck. The fact that adult insects arc partly On a gcncral notc, Hap1ochromi.s was cxogcnous makcs them a rarc food itcm in abundan~aL all dcpths bclwcen 4m and thc lakc, hcncc Lhc high compctition SOm, but catches diminished below this. rccordcd among thc inscctivores. Thcrc Ancarliermon: extensive survey conducted was no loss of condi~ionin fishes having in Lakc Vic~oria(Kudhongania and parasites, even among thosc heavily Cordone, 1974) produccd a similar rcsul~. inlesled. This was also confirmed by Lhc Not much discrepancy existcd belwecn Miinn-Whitncy non-parametric test that earlier survey and the present one with (Z=I .2888) which showcd no significant rcgard to the percentage catch contribution dillcrencc between parasitizcd and no- of Haplochromis. This obcrvation was also parasi~izcdfishes. A happy cocxistcncc confirmed by Bcnda ( 1977), who workcd on the changing densities of Haplochromis Benda. R.S. .md 0. .M. .Mainga. 1977. Distribution and population dynamics of seventy four Haplochranis over the years. But with the total invasion groups in the Kenyan waters of Lake Victoria. of the Gulf by the Nile perch from 1976 EAFFRO Rep. onwards, this distribution pattern of Burd. A.C. 1962. Growth and recruiunent in the herring of the sounhem Nonh Fishery Invest. Lond. Ser. 2.23. Haplochromis no longer exists. De Silver. S.S. 1973. Aspects of hereproductive biology of the sprat, Sprals sprals (L) in inshore waters of Acknowledgements Ihe West Coast of Scotland. J. Fish. Biol. 5.689- 705. Dunn, I.G. 1975. Ecological notes on the Haplmhromis I thank the staffof thedefunctEAFFR0 (Pisces: Cichlidae) species-flock of Lake George. who assisted in the important task of data Uganda (East Africa). J. FiFh. Biol. 7,651-666. Fryer. G. 1969. The troph~cinterrelationships and ecology collection, both in the lake and in the of some littoral communities of Lake Nyasa wilh laboratory. In particular J. Olonde, D. special reference to the fishes. and discussim of the Magero. Odtiiambo. A. Mwangi, G. evaluationofa groupof rock frequenting Cichlidae. F. Proc. Zool. Soc. Lond. 132. 153-18 1. Isyagi, W. Odongo, 0. Arende, J. Kuya, Gupta, S. 1975. Smc observations on rhe biology of and several others without whose effort Cirrhinus reh (Cuvier). J. Firh. Biol. 7. 71-76. Iladcy, P.H.T. 1948. Food and feeding relationships in a this work could not have been done. I am community of freshwater fishcs. J.Anh. Ecol. 17, deeply indebted to Drs. R. Benda and R. 1-13. Muller, formerly of U.S.A.I.D., Kisumu, Kudhongania, A.W. and A. J. Cordonc. 1974. Bathospaual distribution pattern and biomass estunales ofmajor who collaborated with me in most stages demcrsal fishes in Lake Victoria. rtjr J. Trop. of the research. tlydrobiol. Fish. 3,15-3 1. Nlkolsky, G.V. 1963. Ihe Ecology of Fishes. Lundon: Academic press. References Okera, W. 1974. Morphornetrics, condition md gonad dcvclopmcnt of theEast African Sardinelldgibbma Achicng, A.P. 1990. 'Iheimpactolthc lnvodueuonolNilc (Breaker) and Sardinelid albelld (L'alencicnn) J. pcrch, Lores niloricw (L.) on lhc fisheries of lakc Fish. Biol. 6, 801-812. Victoria, J. Fish. Biol. 37 (Supp.A) 17-23. Out, G. 1986. Tilapia producuon in floating net cages. Bancgal. T.B. 1967. A shon rcvicw of lish fecundity. In Ame boff Kg. Pollution Cataloguc. lnstcm. Wcst S.D. Gcrking (Ed.) "Thc Biological Basis of Gcnnany. 1:reshwatcr Fish l'roduction" pp. 89-1 1 I. Oxford, Papema, 1. 1973. Ilosts, distrihu~ionar~d pathology of Blackwell Scientific Publications. infections w~thlarvsc of Eusrrongylides Benda. K.S.1977. Standing s~ockdensity csuma~es(Kg/ (Dioctophymidac, Scmatda) in fishcs irorn liast ha) lor fish from 1969 lhrough 1970 USDPI1:AO African Lakcs. J. I.'L\-~.Biol. 6. 67-76. 1975 EAIJr;KO and 1977 F1.N trawl survcys m hr,J.11. 1974. Uiostadsuwl Analysis. Prenucc llall lnc. Nyanw Gulf. EAl:lXO Rep Kisurnu. Englcwwd Cliifs, Sew Jcrsey.