Studies On Some Aspects Of The Biology Of The Catfish Bagrus Docmac Forsk (pisces Bagridae) In Lake Chamo Ethiopia

Some aspects of the feeding, reproduction, condition and lengthrnweight relationship of the catfish, Bagrus docmac were studiedrnfrom February 1995 - February 1996 in Lake Chamo, Ethiopia. Arntotal of 534 fish samples ranging in size from 33.1-99.1 cmrnfork length (FL) and 500-17400 g in weight were investigated.rnThe length-weight relationship for B. docmac was expressed by:rnTW = O. 0054FL3 . 24 • The Clark's condition factor was calculatedrnfor both sexes separately. The mean monthly condition valuesrnof the males ranged from 0.436 ± 0.011 to 0.489 ± 0.014 whilernthat of the females ranged from 0.449 ± 0.011 to 0.489 + 0.012.rnThe diet of B. docmac was composed of insects, aquatic snailsrnand different fish species. Insects were identified as larvae,rnnymphs and adults. The identified prey fish species werernSynodontis schall, Labeo horii, Oreochromis niloticus, Barbusrnsp. and Hydrocynus forskhalii. Some unidentified fish remainsrnwere found due to partial digestion. Small B. docmac « 40 cmrnfork length) ingested more insects than fish. The large fishrnwas found to be piscivorous, and fish constituted more than 98%rnof the diet by weight. S. schall was the most important preyrnfish, and occurred more than 81% of all food items of B.rndocmac. The S. schall (prey) and the B. docmac (predator)rnlength ratio ranged betvleen 1: 2 and 1: 6 .rnSex ratio (male to female) of B.docmac was 1:1.07 in the totalrnsample, and not significantly different from 1:1 (X 2 = 10.9;rnp > 0.05). Among various length classes sex ratio wasrnsignificant only in fish ~ 80 cm fork ler.gth (X 2 = 5.18; P >rn0.05). Males mature at a smaller size than females. The sizernat 50% maturity of the males was found to be 68.0 cm forkrnlength while that of the females was 68.6 cm fork length.rnAn extended breeding period from February-August with spawningrnpeak in May was observed for both males and females. Pulses inrnbreeding activity occurred in the rainy seasons of the lakernregion.rnThe estimated number of eggs in the ovary was ranged fromrn94442-615674. The ripe ovaries contained from 989-2100 eggsrnper gram of wet weight vlith the mean number of 1474 eggs/g ofrnovary. Fecundity was positively related with fork length (r2rn= 0.64, P < 0.05), body weight (r2 = 0.72, P < 0.05) and gonadrnweight (r 2 = 0.90, P < 0.05).

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