The Effects of Species Interaction and Pond Stocking Density on Tilapia Aquaculture:

Abstract

This paper describes the effects of predatory catfishes Clarias gariepinus (Burchell) and Heterobranchus bidorsalis (Geoffrey Saint-Hilaire) and pond stocking density on the culture of tilapia species which display different parental care strategies. In the presence of catfishes, the maternal mouth-brooder O. niloticus (Linnaeus), and the bi-parental mouth-brooder S. galiliaeus (Steindachner) reproduced easily. However, the substrate-brooder T. guineensis (Bleeker) bred with difficulty as the persistent, aggressive, bottom feeding habit of the catfishes inhibited reproduction to some extent by destroying spawning nests and killing developing eggs, or by frightening the breeders to abandon ventilation and parental care of developing eggs inside the nests. Therefore the control of tilapia overpopulation with predatory catfishes to enhance tilapia growth is more likely to be successful in substrate-brooders than in mouth-brooders. T. guineensis was also more susceptible to direct catfish predation than either O. niloticus or S. galilaeus probably because of its more attractive body colouration. When the three tilapia species were reared together, T. guineensis built spawning nests almost exclusively in the shallow littoral zone, whereas O. niloticus and S. galilaeus concentrated their nests in the deeper part of the pond. Site-dependent segregation of the tilapia species at the time of breeding could be a strategy to avert inter-specific territorial competition. Offspring population of O. niloticus showed an inverse relationship with pond stocking density. As stocking density was increased, agonistic encounters between territorial males intensified and inhibited successful fertilization and recruitment. Growth rate of O. niloticus decreased with pond stocking density up to 3 fish/m2, but the differences were not significant. Journal of the Ghana Science Association Vol. 10 (2) 2008: pp. 12-19