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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. [ABSTRACT FROM AUTHOR]

Enzymes synthesized by the gut microbiome are recognized as vital for assisting host metabolism. This study was conducted to screen and identify bacterial isolates with enzyme‐producing abilities from the intestine of milkfish Chanos chanos. Overall, 114 isolates were collected, of which 58% showed clear zones indicating various enzyme activities via plate‐based assays. Specifically, 65 isolates were amylolytic, 1 isolate was cellulolytic, and 18 isolates exhibited both activities. The two most promising isolates—CC8 and CC27—were further subjected to spectrophotometric enzyme assays to determine their amylase, cellulase and protease activities. Results showed that amylase, cellulase and protease activities (6.00 ± 0.01, 0.52 ± 0.02 and 18.62 ± 0.16 U mg−1 protein, respectively) were higher in CC8 than in CC27. Using 16S rRNA gene sequencing, the isolates were putatively identified as Vibrio sp. and Bacillus cereus respectively. At a suspension (mL) to feed (g) ratio of 3:25, dietary supplementation of putative probiotics was carried out to evaluate the growth performance, survival and enzymatic activities of juvenile Nile tilapia Oreochromis niloticus. Results revealed that probiotic‐supplemented fish exhibited better growth performance—final average body weight, weight gain, specific growth rate and feed conversion ratio—along with increased intestinal enzymatic activities compared with the control (p < 0.05). Survival rates ranged from 80% to 90% and were statistically similar in all treatments (p > 0.05). This study concludes that the application of Vibrio sp. CC8 and Bacillus cereus CC27, supplemented either in monostrain or multistrain preparation, can promote growth and enzymatic activities in juvenile Nile tilapia. [ABSTRACT FROM AUTHOR]