Metabolic effects on growth and muscle of soya-bean protein feeding in cod (Gadus morhua)

Abstract

The aim of the present study was to investigate the effect of soya-bean protein on growth and muscle metabolism in fish. Cod,Gadus morhua, were fed on a fish-feed formula with the high-quality fish-meal protein being replaced by 100, 200 or 300 g soya-bean protein/kg fish-meal protein. The feeding experiment lasted for 43 d at a water temperature of 7–8º and a sea water salinity of 3.5%. At the 200 g/kg level of soya-bean protein, food intake and growth rate were similar to those of the controls. At the 300 g/kg level of soya-bean protein, food intake was diminished by 6 % and growth by 67 % relative to control levels. In muscle, sarcoplasmic protein (/g wet weight) was significantly decreased by 14%. Myofibrillar protein (/g wet weight) was unchanged. Levels of RNA in the myofibrillar fraction decreased at all three levels of soya-bean protein, and that of the sarcoplasmic fraction decreased at the highest level of legume-protein. With increased levels of soya-bean protein, RNA: DNA declined by 18% from 1.88 to 1.54. The contractile protein myosin heavy chain (/mg protein and /g wet weight) and myosin heavy chain-specific mRNA (/mg RNA) were not significantly affected by dietary conditions. Expressed per g wet weight, the decline by 21 % of the specific mRNA depended on the total RNA content which decreased with the increase in soya-bean protein. Acid proteinase activity was lowest at the 200 g/kg level, showing a decrease of 23%. Glycogen content fell by 46% at both the 200 and 300 g/kg level of dietary soya-bean protein. The results show that muscle metabolic functions responded to the dietary plant protein before there were any measurable changes in growth rate. From the results it is concluded that 200 g/kg or less of the high-quality fish-meal protein may be replaced by soya-bean protein in a fish-feed formula.