Prediction of cannibalism in juvenile Oreochromis niloticus based on predator to prey weight ratio, and effects of age and stocking density

Factors influencing size-dependent cannibalism in Nile tilapia, Oreochromis niloticus, were investigated in controlled conditions. First, individual-based trials were conducted to develop a linear regression model to predict the occurrence of cannibalism based on body measurements. Oral gape (G, mm), body depth (D, mm) and weight (W, g) of 140 fish were measured and we estimated maximum prey weight (Wprey) for a given predator weight (Wpredator): Log10Wprey = 1.03Log10Wpredator − 1.13. This model was verified by conducting 76 single pair trials. The revised model based on observed cannibalism is: Log10Wprey = Log10Wpredator − 1.17. Several experiments involving a group of prey and predators were conducted to elucidate the relative importance of factors that influence cannibalism. Cannibalism was significantly affected by stocking density, age of fish and predator/prey weight ratio. Logit models of mortality data of both the individual-based and observations based on a group of predators and prey estimated R50 (the predator/prey weight ratio at which an encounter of a predator and prey resulted in a predation success of 50%) to be 14.6 and 14.8, respectively. The results of these experiments can be used to reduce fry losses due to cannibalism.