REPLACING DIFFERENT PROPORTIONS OF FISHMEAL WITH HERMITIA ILLUCENS MEAL ON THE GROWTH, HEALTH AND MUSCLE QUALITY OF MICROPTERUS SALMOIDES

Four diets with isonitrogenous and isolipidic (45% protein and 15% lipid) were prepared. The control group contained 30% fish meal (FM30), while the other three groups replaced 16.67% (FM25), 33.33% (FM20) and 50% (FM15) fish meal with black soldier fly (Hermitia illucens) larvae meal respectively. The juvenile largemouth bass (Micropterus salmoides) was fed four diets in the indoor circulating water system for 8 weeks respectively. This study aimed to examine the impacts of replacing fish meal with H. illucens larvae meal on the growth performance, health and muscle quality of M. salmoides. The results showed that there was no significant difference in final body mass, weight gain rate (WGR), specific growth rate (SGR), and survival rate among the four groups (P>0.05). However, the FM20 group exhibited a high WGR and SGR and a lowest feed conversion ratio (FCR), which was significantly lower than that of FM15 and FM25 (P<0.05). Partial replacement of fish meal with H. illucens larvae meal reduced the lipid content of the whole fish and liver, as well as the serum triglyceride content. Furthermore, it resulted in decreased levels of C14﹕0, C16﹕0, C18﹕1n-9 and C18﹕3n-3 in liver and DHA in muscle. Conversely, there was an elevation in C18﹕0, DHA, EPA and C22﹕5n-3 in the liver. These modifications had a marginal effect on amino acid composition in both muscle and liver. Compared with the control group, the contents of malondialdehyde in foregut and liver of the fish in FM20 group increased significantly (P<0.05), while the activities of alkaline phosphatase in foregut and serum decreased significantly (P<0.05). The intestinal epithelium of the foregut was damaged with impaired intestinal villi and intestinal fold adhesion, the activities of lipase in foregut and the contents of crude lipid in muscle and crude protein in whole fish were the highest, accompanied with the highest DHA in liver of FM20 group. The above results revealed that the largemouth bass M. salmoides had an ability of endogenous highly unsaturated fatty acid (HUFA) biosynthesis. It is suggested that a 50% replacement of fish meal with H. illucens larvae meal (FM15) can be undertaken, with a minimum addition of 15% fish meal in diets of M. salmoides, which has no negative effects on the growth performance. However, the most suitable level is 33.33% replacement of fish meal. This study provides data for the development of nutritionally scientific and reasonable composition and low cost feed for M. salmoides.