Some aspects of the reproductive biology of Tilapia zilli from a Small Lake in Imo State, Nigeria

Some aspects of the reproductive biology of Tilapia zilli from Umuoseriche man-made Lake, in Oguta, Imo State, Nigeria were studied. The overall male/female ratio was 1:1.28. The numbers of male fishes in the smallest size range (135 – 145 mm) and the largest size range (215 – 225 mm) were greater than the corresponding number of females in the same size ranges. In the medium size range (165 – 185 mm), the females however outnumbered the males. Mean gonadosomatic index (GSI) was 1.57 ± 0.79 and mean ovarian weight 1.93 ± 1.12 g. Fecundity was 6754 ± 1576 and varied considerably amongst any particular size range. Fecundity varied by a factor of 1.607 of the total length and 1.52 of the standard length. Fecundity was equally positively related to length and body weight. Spawning was seasonal and was more in the wet season months through to September and seemed to be triggered off by either rainfall or low temperature. Keywords: reproductive biology, Tilapia zilli, Gonadosomatic index, fecundity, ovarian weight, man made lake Animal Production Research Advances Vol. 1(2) 2005: 70-75