Dietary α-ketoglutarate improves the feed efficiency and growth performance of Chinese mitten crab (Eriocheir sinensis) fed low-protein diets by modulating protein metabolism and intestinal health

Developing low-protein feeds is essential for reducing aquaculture costs and environmental impact. This study examined the effects of α-Ketoglutarate (AKG) on growth performance, protein metabolism, intestinal microbiota, and transcriptomic responses in Chinese mitten crab (Eriocheir sinensis) under varying dietary protein levels. A 3 × 3 factorial design was employed in a 56-day feeding trial, with three protein levels (28 %, 33 %, and 38 %) and three AKG supplementation levels (0 %, 0.5 %, and 1 %). Juvenile crabs (1400 ind., 0.58 ± 0.02 g) were randomly allocated to nine treatments with four replicates each. Results showed that low-protein diets (28 % and 33 %) impaired growth and protein deposition. However, AKG supplementation (0.5 % and 1 %) markedly enhanced weight gain (WG), specific growth rate (SGR), and feed utilization across all protein levels. Notably, crabs fed a 33 % protein diet with 1 % AKG achieved similar WG to those fed the 38 % protein diet. AKG supplementation reduced hemolymph ammonia levels, increased hepatic glutamate content, and enhanced glutamate dehydrogenase activity, optimizing nitrogen metabolism. Additionally, AKG improved digestive enzyme activities, upregulated amino acid transporter genes, and activated the mTOR pathway to promote protein synthesis. AKG also enhanced intestinal morphology and microbial composition, thereby improving intestinal health. Transcriptomic analysis further indicated that AKG might mitigate disruptions in extracellular matrix (ECM) receptor interactions and activate the PI3K-Akt pathway, facilitating protein synthesis. This study suggests that low-protein diets inhibit the growth of juvenile E. sinensis, whereas 1 % AKG supplementation enhances nutrient assimilation, nitrogen metabolism, and cellular signaling, ultimately improving feed efficiency and growth performance.