Effects of seasonal temperature and photoperiod on Atlantic cod (Gadus morhua). II. Enzymes of intermediary metabolism

Atlantic cod (Gadus morhua) were held at either constant (∼9°C) or ambient ocean temperatures from December 2000 to June 2002 under natural photoperiod. The activities of gluconeogenic, glycolytic, lipid, and amino-acid-related enzymes were measured in liver and white muscle at eight time points over the experimental period. Principal component analysis reduced the 13 liver enzymes to two factors and the nine muscle enzymes to three factors. Factor scores were used to investigate the effects of season, temperature, and photoperiod on cod physiology. Liver factor I (FI) and muscle factor III (FIII) were significantly correlated with mass and length of the fish. Only liver FI was significantly correlated with tissue metabolites parameters. Significant differences between thermal groups were only observed for muscle FIII in June 2002. This study demonstrates that temperature is not a major factor determining the activity of the selected enzymes in ages-1+ to -3+ cod. Photoperiod and internal physiological cycles are more important in determining liver and muscle enzyme activities. Most liver enzymes measured are better indicators of fish growth than muscle enzyme, and liver protein is the parameter that best correlates with body mass, length, and liver mass.