Dietary protein, lipid and insect meal on growth, plasma biochemistry and hepatic immune expression of lake whitefish (Coregonus clupeaformis)

Studies are lacking that investigate the dietary nutrient requirements of lake whitefish (Coregonus clupeaformis), a newly farmed fish species in Ontario, Canada. Dietary levels of protein and lipid must be optimized to ensure high growth performance for the commercial success of this species. Additionally, the inclusion of insect meal in the diet may improve growth and immune response. The objective of this study was to evaluate the effects of dietary protein:lipid ratios and insect meal as a feed additive on the growth performance and hepatic immune function of juvenile lake whitefish (301 ± 10 g). A 16-week (112 day) trial was performed with five diets including a commercial control diet (BCC), and four experimental diets with high or low levels of protein (54 and 48%, respectively) and lipid (18 and 12%, respectively). The high protein dietary groups contained 5% of full-fat black soldier fly larvae (Hermetia illucens). Fish weights, viscera, liver, and blood were collected for further analysis. Specific growth rate, thermal growth coefficient and weight gain were significantly higher in fish fed with the BCC and high protein high lipid (HPHL) diets. However, viscerosomatic index was found to be significantly higher in fish fed the BCC diet, thus HPHL is more optimal for non-visceral weight gain. Higher levels of plasma phosphorus, aspartate aminotransferase and potassium indicated poor growth and stress in fish fed low lipid diets. Relative expression of HSP70, involved in cellular repair, was significantly downregulated in fish fed high lipid diets, and no effects were found on the expression of innate immune and oxidative stress genes. Also, IL8 (CXCL8) and catalase were upregulated (non-significant) in fish fed the HPHL diet with the largest weight gain. No effects of insects were found on growth, plasma biochemistry or gene expression, which suggests 5% dietary inclusion was too low. Overall, we recommend a HPHL diet for the cultivation of lake whitefish based on improved growth performance, low viscera weight, improved plasma biochemistry and downregulation of cellular repair genes.