Reproductive Biology of Mouth-Brooding Tilapiines in the Kafue Flood plains

Abstract

Invasive alien species have become a serious threat to the biodiversity of ecosystems of the world. Globally, the threat to biodiversity due to invasive species is considered second only to habitat loss. Invasive species are thus a serious impediment to conservation and sustainable use of global, regional and local biodiversity. This study concentrated on the reproductive biology of the Oreochromis species in the Kafue Floodplains, which is part of the Kafue River stretching from Itezhi-tezhi to the Kafue Gorge. Specific objectives for this study were to compare reproductive strategies i.e. egg size and Gonadosomatic Indices of the introduced Oreochromis niloticus and the local breams, Oreochromis andersonii and Oreochromis macrochir. Oreochromis niloticus is an invasive species that has been reported to cause a reduction in abundance of fish which are closely related to it due to its highly competitive nature. In this study, the egg sizes were noted as longest in Oreochromis niloticus measuring 1.825 ± 0.1892mm followed by Oreochromis andersonii with 1.696 ± 0.3117mm and Oreochromis macrochir had the smallest, which measured 1.4483 ± 0.777mm. The Gonadosomatic Index was highest in Oreochromis niloticus at 1.034 ± 0.0816 followed by Oreochromis macrochir with 0.918 ± 0.1332 and Oreochromis andersonii with 0.783 ± 0.0107. In all three species, the females had a higher Gonadosomatic Index than the males and the fish in the ripe gonad maturity stage also showed a higher Gonadosomatic Index value than the other stages. Though only six months of data were collected for Gonadosomatic Indices, distinct spawning peaks for all three species were noted as November and January for Oreochromis andersonii, October and December for Oreochromis macrochir and November through December and March for Oreochromis niloticus. From the results, it can therefore be concluded that larger egg sizes and high Gonadosomatic Index of Oreochromis niloticus compared to the other mouth-brooding tilapiines, Oreochromis andersonii and Oreochromis macrochir contribute significantly in giving it a competitive advantage. It is therefore recommended that the introduction of Oreochromis niloticus into the Zambian river systems be revised based on the findings from this study.