Reproductive strategies of the Cichlids in a small reservoir in Ilorin, Nigeria

Abstract

The reproductive strategies of Cichlids: Hemichromis fasciatus, Oreochromis niloticus, Sarotherodon galilaeus and Tilapia zillii was studied from June, 2007 to December, 2008. The variability in egg–size (i.e. diameter) were measured using the micrometer eye-piece in a binocular microscope. Fecundity was estimated by direct enumeration and related to the fish species population. The sex ratio was calculated. The mean egg diameter of H. fasciatus, S. galilaeus, T. zillii and O. niloticus were: 1140 ± 54.74, 1725 ± 95, 1250 ± 129 and 1775 ± 125 mm respectively. There was variability in the egg size with fish species. The mean fecundity were 1100±100 eggs in H. fasciatus , 700 ± 70.71 eggs in S. galilaeus, 1509 ± 34.74 eggs in T. zillii and 366 ± 39.74 eggs in O. niloticus. T. zillii laid the highest number of eggs. In O. niloticus and S. galilaeus eggs were moderate in number but the eggs were fairly large in size. T. zillii employed the strategy of the force of number and parental care to ensure survival of the off-springs. S. galilaeus and O. niloticus employed the strategy of parental mouth- brooding. The reproductive strategy of T. zillii was efficient but the reproductive strategy of O. niloticus was inefficient. The efficient reproductive strategy of T. zillii may have resulted in the abundance of this species. S. galilaeus are biparental mouth brooders and the reproductive strategy was fairly successful as the population of the fish in the reservoir were moderate. Maternal mouth brooding reproductive strategy allows very few eggs to be brooded and this may be responsible for the low population of O. niloticus in the reservoir.

Keywords: Egg diameter, fecundity, Cichlids