Growth Responses and Liver Changes in Juvenile Sunshine Bass (Morone chrysops × M. saxatilis) Associated with Dietary Protein and Lipid Level

Abstract

Four isocaloric semi-purified diets containing 33 or 43% protein with either 13 or 16% lipid were fed to juvenile sunshine bass, Morone chrysops × M. saxatilis, (4.5 g initial weight) for 12 weeks. Fish fed 43% protein and 13% lipid gained significantly more weight than fish fed other diets. Both increased dietary protein or increased dietary lipid resulted in significant increases in total body fat but no change in body protein. Increasing the dietary protein level to 43% also resulted in significantly higher liver lipid content. Histological examination revealed a high degree of fatty infiltration in these livers, which was exacerbated at 16% dietary lipid. Protein efficiency ratios and apparent protein retention were greater in the 33% protein diets. Liver alanine aminotransferase (AAT) activities increased significantly when dietary protein increased. Replacing dextrin with lipid further increased AAT activity. Lipid weight gain and liver composition as well as enzyme activities are responsive to macronutrient changes in the diet.