Influences of Partial Substitution of Fish Meal with Defatted Black Soldier Fly (Hermetia illucens) Larvae Meal in Diets on Growth Performance, Biochemical Parameters, and Body Composition of Juvenile Chinese Soft-Shelled Turtles (Pelodiscus sinensis)

The black soldier fly (Hermetia illucens) larvae meal (BSFM) has been widely applied in aquaculture production due to its rich nutritional value, easy availability, and renewability. However, to our knowledge, it has not been used in the diets for turtles. Here, we evaluated the acceptability of partial substitution of fish meal (FM) with defatted BSFM in the diets of juvenile Chinese soft-shelled turtles (Pelodiscus sinensis). A total of 225 juvenile turtles were randomly divided into D1, D2, D3, D4, and D5 groups, which were fed with BSFM replacing 0, 5%, 10%, 15%, and 20% FM, respectively, for 70 days. The results showed that growth performances of groups D2 and D3 were not significantly different (P>0.05) from that of group D1, whereas the growth performance compromised (P<0.05) in groups D4 and D5. The activity of serum alkaline phosphatase was higher (P<0.05) in group D3 relative to other groups, while alanine aminotransferase and aspartate aminotransferase activities were higher (P<0.05) in group D4 when compared with groups D1, D2, and D3. Liver lysozyme activity and malonaldehyde level were significantly higher (P<0.05) in group D1 relative to other groups, whereas total antioxidant capacity activity showed the opposite trend (P<0.05). The activities of hepatic total superoxide dismutase and glutathione peroxidase displayed a linear elevation (P=0.011 and P<0.001, respectively) from groups D1 to D3. Intestinal amylase and protease activities linearly increased (P<0.001) with increasing BSFM levels, while intestinal lipase activity showed a quadratic increase and then a decrease with increasing BSFM levels (P=0.011). Muscle crude protein and fat contents increased (P<0.05) in group D3 when compared with groups D1 and D2. Muscle phenylalanine, glutamic, tryptophan, and arginine levels increased in group D1 in comparison with the other groups (P<0.05), whereas the opposite was true for isoleucine and proline levels. The broken-line analysis based on specific growth rate estimated that the optimal level for replacing dietary FM with BSFM is 5.0%, which could elicit benefits on both the growth performance and physiological health condition of the juvenile Chinese soft-shelled turtles.