PATTERNS OF GROWTH AND LIPID DEPOSITION IN COD (GADUS-MORHUA L) FED NATURAL PREY AND FISH-BASED FEEDS

Groups of cod were fed two natural prey types, Prawn and herring, and two herring-based wet diets, one with low and the other with high energy density. Cod fed upon whole herring and enriched-herring paste showed the highest growth rates but tended to store increasing amounts of lipid in the liver. Cod fed upon the leanest diet, prawn, showed, however, better efficiencies of energy and nutrient conversion. The effect of decreasing food particle size, by mincing the herring, was to slightly impair growth and to substantially lower the efficiency of food conversion. The fatty acid compositions of the body lipids tended to reflect dietary input. The major lipid class in the muscle was the phospholipid whereas the main lipid storage depot consisted of triacylglycerols in the liver. There were some indications that either 20:5n-3 was chain elongated to 22:6n-3, or was selective utilized. Dietary 22:1 appeared to have been used as an energy source by the cod, a predator that naturally feeds on prey such as herring which are rich in these fatty acids.