THE INFLUENCE OF DIETARY-LIPID CLASSES ON THE FATTY-ACID COMPOSITION OF SMALL COD GADUS-MORHUA L JUVENILES REARED IN AN ENCLOSURE IN NORTHERN NORWAY

Cod larvae were reared from the yolk sac stage in an enclosure system in northern Norway. After metamorphosis, the juveniles were offered a commercial diet in addition to the natural zooplankton available. From 3 wk after metamorphosis, there was a gradual increase of the commercial diet in gut contents, and by Day 55 most of the diet consisted of this food. Specific growth rate (SGR) was 19.5%.day-1 during the first 3 wk after metamorphosis, but decreased to 6.5%.day-1 during the subsequent 5 wk. Analysis of fish, zooplankton and the commercial diet indicated that the fatty acid composition of cod neutral lipids in particular, was significantly influenced by the polar lipid classes of the zooplankton during the first 3 wk after metamorphosis. Thereafter there was an increase in the fish triacylglycerols of 18:1 (n-9), 20:1 (n-9) and 22:1 (n-11) fatty acids which were typical for the neutral lipid classes of both the live food and the artificial diet. It is suggested that cod larvae and small juveniles may have low digestibility of neutral lipid classes due to a lack of suitable lipases, bile acids or both. During larval and early juvenile periods cod may have an absolute need for polar lipids both for the supply of energy and for essential fatty acids.