Cannibalism is a common phenomenon in grouper larviculture. Cannibalism is also found among hybrids of male giant and female brown-marble groupers. However, cannibalization-associated suffocation is usually observed in larviculture of this type of hybrid grouper. To explain cannibalization-associated suffocation in the hybrid, this study measured the hybrid’s mouth width (MW), body depth (BD), and total length (TL) and derived an equation for the cannibal–prey total length (TL) relationship based on a combination of the 2 linear equations of MW-TL and BD-TL for the hybrid. The reliability of this equation was checked using a quadratic equation fitted from observations in which the cannibal’s MW was equal to the maximum BD of its possible prey. Also, morphometric differences between the hybrid grouper and its parents were compared in this study. These comparisons indicated that the morphometric characteristics of the hybrid grouper appear to be more similar to those of its maternal parent in terms of having a relatively small MW which in turn results in a higher incidence of failed cannibalism causing both fish die. We surmise, moreover, that routinely grading the hybrid grouper would not produce as good of an effect as is seen among other groupers due to the cannibalization-associated suffocation seen in the hybrid grouper. Thus, in addition to grading, other manipulations such as weaning of the fry from live organisms to artificial pellets, increasing feeding frequency, and optimal stocking densities should be applied to reduce cannibalism among the hybrid.