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 brownmarbled grouper (E. fuscoguttatus). The cannibal cannot engulf the entire prey and the two ¢sh ultimately end up dying together. Herein, we attempted to compare morphometric di¡erences among orange-spotted, giant and brown-marbled grouper. We established a cannibal^prey total length (TL) relationship for brown-marbled grouper: TL prey 5 0.71 TL cannibal À1.75. According to the equation, a di¡erence 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 di¡erence 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 e¡ect in brownmarbled 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 brownmarbled grouper.
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