Evaluation of common housefly Musca domestica maggot meal as partial substitution of fish meal and fish oil in Chinese mitten crab Eriocheir sinensis diets

The declining availability of fish meal (FM) and fish oil (FO) poses a challenge to the sustainable development of aquaculture, necessitating the exploration of nutritious and eco-friendly alternatives. This study evaluated the effects of partially replacing FM and FO with housefly Musca domestica maggot meal (HM) on the growth performance, nutritional composition, antioxidant capacity, and non-specific immune response of Chinese mitten crab Eriocheir sinensis. An 8-week feeding trial was conducted using six isonitrogenous (crude protein ≈ 42.0 %) and isolipidic (crude lipid ≈ 8.1 %) diets, with HM inclusion levels of 0, 54, 107, 161, 214, and 268 g/kg, corresponding to FM replacement levels of 0, 50, 100, 150, 200, and 250 g/kg, and FO replacement levels of 0, 4, 7, 11, 14, and 18 g/kg. A total of 240 crabs (120 males: 21.16 ± 4.09 g; 120 females: 21.04 ± 3.75 g) were randomly distributed into 30 tanks (4 crabs/tank; ♂:♀=1:1). Results showed that replacing FM and FO with up to 268 g/kg HM (71.4 % FM and 45 % FO) had no significant impact on growth performance or somatic index. Hepatic lipid, protein, essential amino acid, bitter amino acid and total amino acid increased with HM inclusion levels, while antioxidant capacity and lysozyme activity showed a quadratic relationship, peaking at specific HM inclusion levels before declining. Diets containing 214 g/kg and 268 g/kg HM promoted protein and lipid deposition in the hepatopancreas. Furthermore, HM inclusion levels of 161–268 g/kg significantly improved amino acid profiles in muscle and hepatopancreas, as well as fatty acid profiles in the hepatopancreas. HM supplementation also enhanced hepatic antioxidant capacity and lysozyme activity, with optimal effects observed at 132.22–228.77 g/kg. These findings demonstrate the potential of HM as a sustainable alternative to FM and FO in E. sinensis diets, with an optimal inclusion range of 132.22–228.77 g/kg.