Effects of plant-based diets on glucose and amino acid metabolism, leptin, ghrelin and GH-IGF system regulation in Atlantic salmon (Salmo salar L.)

To investigate effects on glucose and amino acid (AA) metabolism and neuroendocrine regulation of energy homoeostasis and GH-IGF system growth regulation, Atlantic salmon were fed high levels of plant protein (PP) and vegetable oil (VO) for 1year and compared to fish fed intermediate levels or a control diet based on fish meal and fish oil. All plant-fed groups had reduced liver glucokinase mRNA and increased muscle glycogen compared to the control group. As digestible starch was highest in the control diet, the increased muscle glycogen might be related to other factors such as lower levels of lysine or higher levels of glucogenic AAs. There were minor effects on transcription of genes related to leptin, ghrelin and GH-IGF system. However, muscle growth hormone receptor was elevated in fish fed high PP, probably related to lipolytic action in these fish. Fish fed high levels of both PP and VO simultaneously had elevated plasma alanine aminotransferase and glucose and of pentose phosphate pathway enzymes. Furthermore, this group had elevated concentrations of some free AAs, especially proline. These results support interaction effects when both high levels of PP and VO are used together, which needs to be considered in the formulation of aquafeeds.