Studies on Some Aspects of , the Biology of the Catfish Bagrus Docmac Forsk (Pisces: Bagridae) in Lake Chamo, Ethiopia
No Thumbnail Available
Date
1996-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
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).
Description
Keywords
Biology