Effects of Glutamine Dipeptide-Supplemented Formulated Diet Substituting Chilled Trash Fish in Chinese Mitten Crab (Eriocheir sinensis)

Feeding Chinese mitten crabs with fresh-frozen fish causes nutritional imbalance and increases disease risk. Compound feed offers better nutrient balance but still requires improvements in palatability and growth performance. This study evaluated the effects of replacing fresh-frozen fish with glutamine dipeptide-supplemented formulated diet on growth, hepatopancreas health, and edible quality, aiming to inform feed formulation strategies. A five-month feeding trial (June-October) was conducted with two treatments: the experimental group received only glutamine dipeptide compound feed, while the control group was fed a mix of fresh-frozen fish and compound feed. Crabs in the experimental group showed significantly higher body weight, length, and width. No significant differences were found in the hepatopancreatic index, gonadosomatic index, meat yield, or total edible yield. In October, the experimental group showed lower malondialdehyde (MDA) levels in the hepatopancreas and higher alkaline phosphatase (AKP) and acid phosphatase (ACP) activities in males. In females, hemolymph AKP and ACP were higher in the control, while glutamic pyruvic transaminase (GPT) was higher in the experimental group. Whether this is related to a potential risk of liver damage or a reaction at a special stage remains to be further verified. Digestive enzyme activities (protease, lipase, amylase) were generally higher in the experimental group, particularly in August (<i>p</i> < 0.05). In October, protease activity in females and lipase activity in males were significantly higher than in controls (<i>p</i> < 0.05). Nitrogen and phosphorus retention in muscle was also significantly higher, indicating better nutrient utilization (<i>p</i> < 0.05). Overall, these findings indicate that a glutamine dipeptide-supplemented diet provides a more effective and sustainable alternative to fresh-frozen fish over a five-month rearing period, improving digestive physiology, feed efficiency, growth performance, and edible quality and flavor.