Differences in growth and chemical composition between male and female farmed cod (Gadus morhua) throughout a maturation cycle

The growth of farmed cod fed to satiation under natural conditions in the sea in North Norway (67 degrees N) was followed over 1 year. At the start of the experiment in September 2003, the average weight was 1300 g. After 1 year, in September 2004, the average weight was 2800 g. From the end of November to June, the fish matured and spawned and there was little or no weight gain in the fish during this time. The male cod developed gonads earlier than the females. In February, the male gonad index was 19% and decreased to 7% by the end of April, whereas the female gonad index increased from 14% in February to 25% in April. The male liver index decreased by 2% in February and by another 3% in April, when it only decreased by 1% in the female cod. The muscle protein in the female cod was reduced by more than 20 g kg(-1) in April, and the difference between the muscle protein in the male and the female cod was still significant in September. No differences were found in the post-rigour muscle pH due to the sex of the fish.