Modulation of physiological performance and intestinal bacterial communities by reduced dietary protein in juvenile redclaw crayfish Cherax quadricarinatus.

Abstract

Previous studies on the optimal protein requirements of freshwater crayfish Cherax quadricarinatus juveniles have mainly focused on growth performance, with limited attention to nutritional physiology and changes in the intestinal microbiome. This study evaluated the effects of reduced dietary protein levels (25%, 30%, 35%, and 37%) on digestive enzymes, energy reserves, hemolymph metabolites, intestinal microbiome, and hepatopancreas histology of juveniles fed for 150 days. The experimental diets were formulated using fish and shrimp meals as animal protein sources, and wheat, rice meals, and corn starch as plant ingredients. While growth and survival were unaffected by dietary protein, juveniles fed the 25% showed reduced lipase activity, increased hepatopancreatic lipid content, lower glycogen reserves, and higher hemolymph glucose concentration. These changes in nutritional physiology were likely influenced not only by dietary protein level but also by interactions among the ratios and sources of dietary protein, lipids, and carbohydrates. The intestinal microbiome of juveniles fed the 25% diet exhibited shifts in bacterial communities and an overall reduction in 20 metabolic pathways. Our results support the use of diet with 25% crude protein in C. quadricarinatus culture during these early stages, at least temporarily, offering potential economic benefits by reducing feed costs without compromising productive efficiency. This study expands our understanding of the deployed physiological strategy and contributing to the development of balanced diets for juveniles, but also provides new insights into changes in the intestinal microbiome of the species when fed different protein diets.