EFFECTS OF DIETARY-COMPOSITION AND ENERGY CONTENT ON THE NUTRITIONAL ENERGETICS OF COD, GADUS-MORHUA

Rates of weight gain did not differ significantly between groups of cod fed either low-energy wet feeds or moist diets of differing composition, but feed intakes and utilization efficiencies did differ between the groups of fish fed the different diets. Both feed utilization efficiency (g gain per MJ feed) and protein efficiency ratio (g gain per g dietary protein) were better for fish fed wet feeds than for those fed the moist diets. Best growth and feed efficiencies were, however, achieved by cod fed on a mixture of coarsely chopped herring, Clupea harengus, and wet feed. Patterns of energy deposition differed between groups of cod fed the different diets. Lipid accumulation in the liver was enhanced by lipid-rich and high-energy diets, whilst low-energy and high-protein diets promoted greater nutrient deposition in the form of muscle tissue (fillet). Large (1.5 kg and over) cod can achieve good rates of weight gain when fed on diets with protein energy:total energy ratios (PE:TE) of 0.40-0.45, without overexcessive deposition of liver lipid, provided that the diets are supplied as coarsely ground, low-energy feeds.