BREEDING SEASON, MATURATION AND FECUNDITY OF OREOCHROMIS NILOTICUS L. (PISCES: CICHLIDAE) IN LAKE CHAMO, ETHIOPIA.

Abstract

The reproductive biology of Oreochromis niloticus in' Lake Chamo, Ethiopia was studied from samples collected every month for a period of thirteen months between March 1996 and March 1997. A total of
1349 fish ranging in size from 125 to 610 nun total length (TL) were caught using gill nets (120, 140, 200 and 240 m:m, stretched mesh). The mean monthly gonadosomatic index (GSI) of the males ranged from 0.21 to 0.61 whereas that of females ranged from 0.75 to 1.61. Higher GSI values were observed between March and June for females and between March and May for males. The pattern of gonad development for both sexes was more or less similar. Ripe males occurred at high frequency (ranged: 39- 60%) between March and May whereas high frequency of ripe females (ranged: 47-53%) occurred between March and June. Thus, it was concluded that O. niloticus in Lake Chamo spawns throughout .the year with peak breeding activity between March and June. The smallest sexually mature female was 385 nun TLI whereas the male was 395 rom Tt. However, the 50% maturity length was about 420 mm TL for both sexes. 0 niloticus were all mature above 500 rom TL. Mean fecundity of O. niloticus was 2493 ± 300, N = 209 (ranged: 390-540 mm TL and 1300-2650 g total weight). TIle smallest count was 1047 (fish length = 420 rom TL) whereas the'largest was 4590 (fish length = 510 rom TL). In general, fecundity of O. niloticus in Lake Chamo was linearly related to total length (F = 201.85TL - 6801), total weight (F "" 1.91rw -1197.8) and gonad weight (F = 55.59Gw + 467.2).