Carbon stable isotope evidence for the contribution of supplemental diets to the growth of brown-marbled grouper (Epinephelus fuscoguttatus Forsskål 1775)

The objective of this study was to evaluate the relative contribution of two supplemental diets (soybean meal [SM] and beer yeast [BY]) to the growth of juvenile brown-marbled grouper (Epinephelus fuscoguttatus Forsskal 1775). The juvenile groupers were fed fish meal (FM) as the main protein source, and 10% SM, 20% SM or 10% BY as supplemental diet with contrast carbon stable isotope (δ13C) ratios. The final δ13C ratios of the fish muscle tissue fell between those of FM and supplemental diet, suggesting that the supplemental diet was assimilated by fish. Estimates using a two-source isotope mixing model showed that the juvenile groupers used approximately equal amount of SM relative to the supplied amount at 10% level, but used less than the supplied amount when fed 20% SM. The fish also showed unbiased assimilation of BY relative to the supplied amount (10%).