Metabolic insights in Arctic charr (Salvelinus alpinus) fed with zygomycetes and fish meal diets as assessed in liver using nuclear magnetic resonance (NMR) spectroscopy

Fish meal is the major source of animal protein in feed for cultured salmonid fish, but its availability is limited and it must eventually be replaced by alternative protein-rich feed ingredients. Zygomycetes (Rhizopus oryzae) is a fungus with protein-rich biomass that could replace fish meal protein in fish feed. Using an 1H NMR spectroscopy approach, we studied the metabolic pattern in liver tissues of Arctic charr (Salvelinus alpinus) fed a commercial diet with unknown composition (ST), a diet with all protein from fish meal (FM) and a diet with most of the protein from zygomycetes biomass (FZ). No significant difference (p >0.05) was found in spectral data between FM and FZ using the OPLS-DA fitted model. However, other models showed that diet ST clearly differed (p<0.05) from diets FM and FZ. Signals for acetate, b-alanine, choline, creatine, formate, glucose, inosine, lysine, SN-glycero-3-phosphocholine and two unknown metabolites were higher in fish fed diets FM and FZ than in fish fed diet ST. These results show that the metabolic profile in liver of Arctic charr will remain unchanged if fish meal protein is replaced with zygomycete protein, suggesting similar physiological responses to both feed ingredients. In contrast, feeding a commercial diet altered the metabolic fingerprint compared with diets FZ and FM, suggesting important differences in ingredient composition and the physiological response to this diet.