Effects of substituting fishmeal with barley worms (Zophobas morio) in diets on growth performance, serum parameters, Immunocompetence, and intestinal health of juvenile leopard coral grouper (Plectropomus leopardus)

This study investigated the effects of replacing fishmeal with barley worm meal (ZMM) on the growth performance, serum indices, immunocompetence, and intestinal health of juvenile leopard coral groupers ( Plectropomus leopardus ). Experimental diets included a fishmeal-based control (FM) and five diets where barley worms replaced 5 %–40 % of fishmeal (labeled ZMM5 to ZMM40). Replacing up to 20 % of fishmeal with ZMM did not significantly affect the growth performance, muscle composition, or activities of key antioxidant and immune enzymes in juvenile leopard coral groupers. Notably, low levels of ZMM supplementation enhanced the intestinal mucosal fold width (VW) and muscular thickness (MT). High substitution (40 %) significantly increased the relative abundance of Sphingomonadaceae in the gut microbiota. The findings indicate that dietary ZMM can effectively replace up to 20 % of fishmeal in juvenile leopard coral grouper diets while maintaining growth, muscle quality, and antioxidant capacity. The optimal inclusion range is 5 %–10 %, which may further improve intestinal morphology. These results provide a scientific basis for developing sustainable, low-fishmeal feeds using barley worms for this species, though long-term effects and economic feasibility require further investigation. • First study on the effects of replacing fishmeal with barely worm protein in juvenile Striped Bass, filling a research gap. • 5 % replacement significantly increased juvenile fish’s intestinal mucosal fold width and muscle layer thickness. • Determining the optimal substitution ratio < 20 % provides a basis for low-fishmeal grouper feed formulations.