Impact of Dietary Carbohydrate Levels on Growth Performance, Feed Efficiency, and Immune Response in Litopenaeus vannamei Cultured in Biofloc Systems.

Background/Objective: Over an eight-week period, this study assessed the influence of dietary carbohydrate levels on growth, metabolism, and immunity in Pacific white shrimp (Litopenaeus vannamei) raised within a biofloc technology (BFT) system. Methods: Five isonitrogenous and isolipidic diets, spanning carbohydrate levels from 11% to 47%, were evaluated. Results: The results showed that dietary carbohydrate significantly impacted both growth performance and feed utilization. The diet containing 38% carbohydrate yielded the best outcomes, resulting in the highest weight gain, specific growth rate, and an optimal feed conversion ratio in the shrimp. Hepatopancreatic metabolic analysis revealed that the shrimp adapted to diets high in carbohydrates through the upregulation of glycolytic enzymes (PK, PFK) and downregulation of gluconeogenic enzymes (PEPCK, G6Pase). By optimizing the water quality and supplementing microbial nutrition, L. vannamei in the BFT system exhibited enhanced dietary carbohydrate utilization and strengthened innate immunity. Specifically, SOD and CAT activities remained largely unaffected by varying carbohydrate levels. However, excessive carbohydrate intake still induced oxidative stress. The high-sugar group (47%) exhibited a significant increase in hemolymph MDA content (p < 0.05), with corresponding metabolic alterations observed in glucose, triglyceride, and total protein levels. On the basis of the results of this study, the BFT system may mitigate the adverse effects of a high-carbohydrate diet by enhancing lysosomal enzyme activity (e.g., ACP) and increasing total protein levels. Conclusions: These findings suggest that the BFT system enhances shrimp immunity and mitigates the potential adverse effects of imbalanced dietary components. Piecewise regression analysis determined the optimal dietary carbohydrate level for shrimp within the BFT system to be 31.44-31.77%.