What causes cannibalization-associated suffocation in cultured brown-marbled grouper,Epinephelus fuscoguttatus(Forsskål, 1775)?

Abstract

During culture of grouper, cannibalism is a frequent phenomenon that usually causes economic loss. Grouper culture often requires grading to prevent size-dependent cannibalism. In comparison with orange-spotted (Epinephelus coioides) and giant grouper (E. lanceolatus), failure to swallow prey during cannibalism is frequently observed in brown-marbled grouper (E. fuscoguttatus). The cannibal cannot engulf the entire prey and the two fish ultimately end up dying together. Herein, we attempted to compare morphometric differences among orange-spotted, giant and brown-marbled grouper. We established a cannibal–prey total length (TL) relationship for brown-marbled grouper: TLprey=0.71 TLcannibal−1.75. According to the equation, a difference of approximately 50% in TL is a threshold to use for grading the grouper. This value is much larger than that used (30%) in orange-spotted and giant grouper, and this size difference results in a higher incidence of failed cannibalism attempts in brown-marbled grouper. It is our belief that the standard grading method will fail to produce as good an effect in brown-marbled grouper as is seen in orange-spotted and giant grouper. Therefore, in addition to grading, other manipulations such as satiation feeding, nutritional supplementation and optimal stocking densities should be applied to reduce cannibalism of brown-marbled grouper.