DOES THE AEROBIC CAPACITY OF FISH MUSCLE CHANGE WITH GROWTH-RATES

To ascertain whether growth rate modifies the oxidative capacity of fi sh white muscle, we examined the effects of individual growth rate on the activities of four mitochondrial enzymes in white muscle of the fa st growing Atlantic cod, Gadus morhua. Growth rates were individually monitored in cod held at three acclimation temperatures during experim ents repeated in four seasons. The size dependence of citrate synthase (CS), cytochrome C oxidase (CCO) and beta-hydroxyacyl CoA dehydrogena se (HOAD) activities was established using wild cod ranging from 115 t o 17,350 g. Given their negative allometry, CS and CCO activities in t he experimental cod were corrected to those expected for a 1.2 kg anim al. HOAD activities did not change with size. The specific activities of CCO and CS were positively correlated with growth rate. However, fo r both enzymes, season explained more of the variability than growth r ate or temperature. Season was the only factor to significantly affect the activity of HOAD, while temperature and season interacted to dete rmine glutamate dehydrogenase activity. CS activity was positively cor related with the initial condition of the cod, which differed among th e seasons. The other enzymes did not show this relationship. The indep endent changes of these enzymes suggest that mitochondria undergo qual itative modifications with changes in growth rate, season and size. Al though growth rate and the activities of CCO and CS are positively cor related, the activity of the mitochondrial enzymes is more affected by size, physical condition and season.