Feed Intake, Growth Performance, and Feed Utilization of the Brown-Marbled Grouper (Epinephelus fuscoguttatus) Juveniles Fed a Soybean-Based Diet Supplemented with an Amino Acid Mixture as a Feeding Stimulant

Groupers are highly valued species in the mariculture industry across Asian countries. As carnivorous fish, they require a high-protein diet to support optimal growth. Soybean meal (SBM) is commonly used as an alternative protein source to fishmeal (FM) in grouper feeds; however, its inclusion often reduces diet palatability. This study evaluated the effects of dietary supplementation with a 1% amino acid mixture (AAM)—predominantly composed of non-essential amino acids—as a feeding stimulant on the feed intake, growth performance, feed utilization, and survival of brown-marbled grouper (Epinephelus fuscoguttatus) juveniles fed an SBM-based diet. Three diets were formulated: a FM-based control diet, an SBM-based diet replacing 40% of FM protein (SBM40), and the same SBM diet supplemented with 1% AAM (AAM10). After an 8-week feeding trial, fish fed the AAM10 diet showed significantly higher feed intake (35.5 g/fish) and specific growth rate (1.5%/day) than those fed the SBM40 diet (25.9 g/fish; 1.2%/day), though this performance remained lower than in the control group. Feed conversion ratio, net protein utilization, and protein efficiency ratio did not differ significantly among treatments, suggesting that the AAM supplementation level was not excessive. The highest survival rate (86.1%) was recorded in the AAM10 group, likely due to reduced cannibalism associated with improved feed intake. These results indicate that AAM supplementation can improve the palatability and performance of SBM-based diets for groupers. However, further research is needed to determine the optimal inclusion level required to achieve growth performance comparable to FM-based diets.