The Condition Factor Feeding And Reproductive Biology Of Oreochromis Niloticus L. (pisces Cichlidae) In Lake Beseka (metehara) Ethiopia.

The condition factor , feeding and reproductive biology of O. niloticus from L.rnBeseka , Ethiopia , were studied from samples taken during November 2003 tornNovember 2004. The length - weight relationship of 1028 fish ranging in sizernfrom 4 cm to 24 cm TL and from 6 g to 140 g TW was computed . Thern2 g relationship was curvilinear, and described by TW = 0.0546 X TL ! thernregression equation for females was TW = 0.1005 X TL2'3 and that of males wasrnTW = 0.0742 X TL2'7. Fulton’s condition factor (FCF) was calculated for the totalrnsample as well as for both sexes separately . The mean monthly FCF was highlyrnsignificantly different between sampling months and sexes and the sex by monthrninteraction was insignificant . The mean . i SE ranged from 1.2 ± 0.06 to 2.0 ±rn0.04 for females whereas from 1.3 ± 0.01 to 2.6 ± 0.04 for males. The stomachrncontents of 690 fish ( 200 males and 490 females ) were examined . The stomachrncontents were found to be composed of diverse items. A total of 22 algal generarnbelonging to three families! Cyanophyceae ( blue greens), Chlorophyceae (greenrnalgae ), Bacillariophyceae (diatoms) , were identified . Among the diatomsrnNavicula, Cyclotella, Cymbella and Thallasiossira, from the blue greensrnMicrocysts, Osciiiatoria and Anabena and from the green algae Cosmarium,rnBotryococcus and Scendsmus were the most frequently encountered algal generarnin the stomach of the fish. In addition , foods of animal origin , zooplankton,rnmacrophytes, sand grains and detritus were found in the stomach of the fish.rnGenerally, diatoms and blue greens as a group contributed the bulk of the diet.rnConsidering the average importance of algal genera, Microcysts and Navicula arernthe most important in the diet of the fish in L. Beseka. The smallest sexuallyrnmature female was 6 cm TL whereas the male was 10 cm TL. However, the 50%rnmaturity length (Lso) was 12cm TL for females and 14cm TL for males, and allrnfish above 20cm TL were sexually mature. The average ± SE fecundity of O,rnniloticus ranging in length from 10 to 23cm TL and in weight from 14 to 81g TWrnwas 154 ± 2.8. The smallest count was 110 eggs and the largest was 235 eggs.rnIn general, fecundity of O. niloticus in L. Beseka was linearly related to totalrnlength, total weight and gonad weight. The mean monthly gonadosomatic indexrn(GSI) of females ranged from 0.7 to 3.5 and that of males from 0.6 to 2.1. Therernwas biannual cycle in which GSI increased from February peaking in April andrnfrom August peaking in September. Ripe females and males also occurred at highrnfrequencies in April and September. Hence, it was found that the fish in L.rnBeseka spawned throughout the year, with a peak of activity between March andrnApril and also between August and September.rnKey words/ phrases: Breeding season, fecundity, Fulton’s condition factor,rnL. Beseka, Oreochromis niloticus, stomach contents.

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