Studies on Some Aspects of , the Biology of the Catfish Bagrus Docmac Forsk (Pisces: Bagridae) in Lake Chamo, Ethiopia

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Addis Ababa University


Some aspects of the feeding, reproduction, condition and length weight relationship of the catfish, Bagrus docmac were studied from February 1995 - February 1996 in Lake Chamo, Ethiopia. A total of 534 fish samples ranging in size from 33.1-99.1 cm fork length (FL) and 500-17400 g in weight were investigated. The length-weight relationship for B. docmac was expressed by: TW = O. 0054FL3 . 24 • The Clark's condition factor was calculated for both sexes separately. The mean monthly condition values of the males ranged from 0.436 ± 0.011 to 0.489 ± 0.014 while that of the females ranged from 0.449 ± 0.011 to 0.489 + 0.012. The diet of B. docmac was composed of insects, aquatic snails and different fish species. Insects were identified as larvae, nymphs and adults. The identified prey fish species were Synodontis schall, Labeo horii, Oreochromis niloticus, Barbus sp. and Hydrocynus forskhalii. Some unidentified fish remains were found due to partial digestion. Small B. docmac « 40 cm fork length) ingested more insects than fish. The large fish was found to be piscivorous, and fish constituted more than 98% of the diet by weight. S. schall was the most important prey fish, and occurred more than 81% of all food items of B. docmac. The S. schall (prey) and the B. docmac (predator) length ratio ranged betvleen 1: 2 and 1: 6 . Sex ratio (male to female) of B.docmac was 1:1.07 in the total sample, and not significantly different from 1:1 (X 2 = 10.9; p > 0.05). Among various length classes sex ratio was significant only in fish ~ 80 cm fork ler.gth (X 2 = 5.18; P > 0.05). Males mature at a smaller size than females. The size at 50% maturity of the males was found to be 68.0 cm fork length while that of the females was 68.6 cm fork length. An extended breeding period from February-August with spawning peak in May was observed for both males and females. Pulses in breeding activity occurred in the rainy seasons of the lake region. The estimated number of eggs in the ovary was ranged from 94442-615674. The ripe ovaries contained from 989-2100 eggs per gram of wet weight vlith the mean number of 1474 eggs/g of ovary. Fecundity was positively related with fork length (r2 = 0.64, P < 0.05), body weight (r2 = 0.72, P < 0.05) and gonad weight (r 2 = 0.90, P < 0.05).