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Effects of fishmeal substitution with Hermetia illucens L on the growth, metabolism and disease resistance of Micropterus salmoides

Identifying suitable substitutes for fishmeal has been one of the important issues for the aquaculture industry for decades. Recently, the black soldier fly, Hermetia illucens L (HI) has become one of the most promising alternative protein substitutes for fishmeal in aqua-diets. This study investigated the effects of fishmeal substitution with fresh HI larvae on growth, serum and liver parameters, intestinal enzyme activity, histomorphology and innate resistance to Aeromonas schubertii in Largemouth bass. Three hundred and seventy-five Largemouth bass were randomly allocated into five groups and fed different diet proportions of HI instead of fishmeal as 0, 5, 10, 15 and 20% HI for 49 days. Results showed that the growth performance of fish, including feed conversion ratio and feed intake were not affected by dietary treatments of 5 and 10% HI. However, the levels of them are significantly increased in 20% HI. Serum alanine aminotransferase content in Largemouth bass fed 20% HI were significantly increased. The liver total protein levels of fish fed 15 and 20% HI were significantly increased, while glutathione peroxidase activity was significantly decreased. In fish fed 5% HI, GSH-PX activity was significantly increased. Intestinal amylase activity of fish fed 15 and 20% HI was decreased. The hepatic and intestinal histomorphology of all fish was unaffected, the intestinal epithelial cells were intact and the intestinal villi were clearly visible. After 49 days, it was found that fish fed 5% HI significantly reduced the amount of A. schubertii colonisation in the spleen at 48 h and 72 h after A. schubertii challenge. It was concluded that the replacement of dietary fishmeal with 5% HI did not alter growth performance, and hepatic and intestinal histomorphology and it improved the antioxidant level and disease resistance of Largemouth bass.