Comparing black soldier fly (Hermetia illucens) larvae versus prepupae in the diets of largemouth bass, Micropterus salmoides: Effects on their growth, biochemical composition, histopathology, and gene expression

Abstract

An 8-week feeding trial was performed to compare the supplementation of full-fat black soldier fly, Hermetia illucens, larvae (BSFL) versus pre-pupae (BSFP) in the diets of largemouth bass, Micropterus salmoides, juveniles. Both BSFL and BSFP were produced in the laboratory from the same batch and ingredients although BSFP tended to have higher protein and amino acid content. Four isonitrogenous and isolipidic diets were formulated including a fishmeal-based control diet (D1), soybean meal-based diet (D2) and soybean meal-based diets with either BSFL (D3) or BSFP (D4) at 4.2% contributing protein (or 11.90 and 9.83%, respectively). Survival, growth, feed intake, muscle/liver fatty acid composition/mineral composition, hepatic/intestinal expression of growth (insulin-like growth factor ‘IGF-I’, growth hormone ‘GH’), lipid metabolism (cholesterol 7 alpha-hydroxylase ‘CYP7A1’, fatty acid synthase ‘FASN’), antioxidant sentinals (superoxide dismutase ‘SOD’), inflammatory cytokines (tumor necrosis factor-α ‘TNF-α’, transforming growth factor- β1 ‘TGF-β1’) representative genes as well as liver/intestinal histopathology were determined. Although survival was similar among treatments, fish growth pattern was D1 > D2 > D3 > D4, with each treatment significantly different than the others. Feed intake was significantly lower in the D4 treatment. Liver and intestinal histopathology were similar between D1 and D2, but intestinal villi were less tightly packed in fish fed D3 or D4 compared to those in the D1 and D2 treatments. In the D4 treatment, liver histology revealed inflammation and necrosis in a third of the fish sampled, while the intestinal villi were significantly shorter and wider, respectively. Nevertheless, for most of the hepatic genes tested, the expression in fish fed D3 or D4 generally mirrored those of the control diet. Although the nutritional value of BSFL and BSFP depends on their diet, this study clearly demonstrates that BSFL is better for M. salmoides compared to BSFP, which may be related to the high chitin content of the BSFP.