RELATION BETWEEN GROWTH-RATE AND METABOLIC ORGANIZATION OF WHITE MUSCLE, LIVER AND DIGESTIVE-TRACT IN COD, GADUS-MORHUA

To determine whether the aerobic capacity of tissues required for grow th specifically reflects growth rates, we monitored the activities of key enzymes of oxidative, glycolytic and amino acid metabolism in musc le, liver and intestine of Atlantic cod (Gadus morhua) growing at diff erent rates. Fish were maintained individually in small tanks at 10 de grees C and fed on rations that allowed growth rates ranging from -0.6 to 1.6% per day. The correlation between growth rate and muscle enzym e activity was pronounced for the glycolytic enzymes (LDH, PFK and PK) . The activities of glycolytic enzymes were more than four times highe r for fish having higher growth rates compared to those that did not g row. Mitochondrial enzyme (cytochrome c oxidase, citrate synthase and beta-hydroxyacyl-CoA dehydrogenase) activities remained unchanged in f ish with positive growth. The liver seems to respond to requirements o f growth by an increase in size. In the liver, the activities of the e nzymes of amino acid metabolism expressed as units mu g DNA(-1) specif ically increases with growth rate. In contrast to the two other tissue s, the specific activities of mitochondrial enzymes in the intestine i ncreased with growth rate while the relative mass of the intestine rem ained constant. Intestinal cytochrome c oxidase activity increased fro m a minimum of about 2 to more than 8 units g intestine(-1) Cytochrome c oxidase activity increased in parallel with the food conversion eff iciency. This suggests that the aerobic capacity of the intestine may initially limit the rates of digestion and growth in this species.