Improving flesh quality of grass carp ( Ctenopharyngodon idellus ) by completely replacing dietary soybean meal with yellow mealworm ( Tenebrio molitor ).

In order to find viable alternative protein sources for aquaculture, we evaluated the effect of partial or complete replacement of dietary soybean meal with yellow mealworm (TM) on the flesh quality of grass carp. In this study, 180 grass carp (511.85 ± 0.25 g) were fed 3 experimental diets in which 0% (CN), 30% (YM30) and 100% (YM100) dietary soybean meal was replaced by TM for 90 d. The results showed that growth performance, biological parameters and serum antioxidant capacity of grass carp were not affected by dietary TM ( P  > 0.05). Both muscle and whole body crude protein were obviously promoted with the increase of dietary TM ( P  < 0.05), and the concentration of heavy metal in muscle was not influenced ( P  > 0.05), indicating that food safety was not influenced by TM. Dietary TM improved muscle textural characteristics by elevating adhesiveness, springiness and chewiness in YM100 ( P  < 0.05). In addition, the muscle tenderness was significantly increased by declining the shear force ( P  < 0.05). The muscle fiber density in YM30 &YM100 and length of dark bands and sarcomeres in YM100 were obviously increased ( P  < 0.05). The expression of myf5 , myog and myhc exhibited a significant upward trend with the increase of dietary TM ( P  < 0.05), which promoted fiber density, length of sarcomere and texture of grass carp muscle. According to the results of metabolomics, the arachidonate (ARA) and eicosapentaenoic acid (EPA) were notably elevated in YM30 and YM100, which indicated that the improvement of flesh quality of grass carp may contribute to the dietary TM influence on muscle lipid metabolism, especially the polyunsaturated fatty acids. In conclusion, TM can completely replace dietary soybean meal and improve the nutritional value of grass carp.