Synergistic influence of hydrolyzed squid processing by-products and Bacillus probiotics as dietary supplements on growth performance, immunological responses, and gut health of juvenile black tiger shrimp fed fishmeal-free diets

Abstract

Protein hydrolysates as a feed supplement have been reported to enhance the growth of beneficial gut bacteria and improve the host’s animal intestinal balance. Thus, this study evaluates the prebiotic effects of hydrolyzed squid by-products in black tiger shrimp, Penaeus monodon, diet. A 50-day feeding trial was conducted following a 4 × 2 factorial experiment in a completely randomized design. The juvenile P. monodon were fed plant-based diet (without fishmeal) supplemented with graded levels of 0, 0.5, 1.0, and 2.0% hydrolyzed squid by-products, either with or without Bacillus subtilis BF12. A control group fed a fish meal-based diet was also included. The shrimp growth, survival, nutrient retention, digestive enzyme activities, immune-related and gut pro-inflammatory gene expression, and intestine histomorphology were the evaluated biological responses. Feeding shrimp with plant-based diet containing 0.5% hydrolyzed squid by-products and B. subtilis BF12 supplement improved growth, enhanced feed conversion, improved nutrient retentions, upregulated the immune-related genes, and downregulated the gut pro-inflammatory genes. Enhanced digestive enzyme activities were observed in treatment groups with higher hydrolyzed squid by-product supplementation. Moreover, hydrolysate supplementation and probiotic application increased the shrimp’s intestinal villi height and promoted the growth B. subtilis BF12 probiotics in the gut. Collectively, the present work suggests that hydrolyzed squid by-product protein supplementation at 0.5% and B. subtilis BF12 probiotics can promote growth, enhance the immunological responses, and improve the gut health of juvenile P. monodon fed a plant-based diet.