Dietary Inclusion of Common Housefly Musca domestica Maggot Affects Nutritional Composition and Health Status in Chinese Mitten Crab Eriocheir sinensis

This study evaluated the effects of partially or completely substituting fishmeal and fish oil with dried housefly (Musca domestica) maggots on the growth, nutritional composition, antioxidant capacity, and immunity of Chinese mitten crab (Eriocheir sinensis). An 8-week feeding trial was conducted using three isonitrogenous and isolipidic diets: T1, a control formulated feed containing 350 g/kg fishmeal and 40 g/kg fish oil; T2, a formulated feed containing 200 g/kg fishmeal and 29 g/kg fish oil, supplemented with 161 g/kg dried housefly maggots; and T3, a formulated feed containing no fishmeal and 15 g/kg fish oil, supplemented with 375 g/kg dried housefly maggots. The results showed that T2 maintained survival and growth comparable to the control while enhancing the HSI, EAA profiles, and n-3/n-6 ratio, along with elevated antioxidant capacities (CAT and GSH-Px) and lysozyme activity. In contrast, T3 increased the EAA, TAA, and EAA-related ratios, while elevating the BAA, atherogenic index and thrombogenic index, but reducing the beneficial PUFA and suppressing immune parameters. Notably, T3 did not induce excessive hepatopancreatic lipid accumulation. A mineral analysis revealed tissue-specific deposition patterns, with muscle accumulating K, Ca, Zn, Cr, and Cu, while the hepatopancreas retained a higher Ca, Fe, and Se. Despite the increased Cr and Cu accumulation with maggot inclusion, all levels remained within safety limits, posing no health risk to crabs. These findings demonstrate that dried housefly maggots represent a viable alternative protein and lipid source for crabs, with 161 g/kg being the preferable inclusion level among the two tested levels. Inclusion at 161 g/kg provides nutritional complementarity with the formulated feed and enhances the immune function, while inclusion at 375 g/kg disrupts the nutritional balance and immunological homeostasis. This study provides a scientific foundation for optimizing maggot-based feeding strategies in sustainable crustacean aquaculture.