Seasonal variations in the gonad size and the protein and water content of cod, Gadus morhua (L.), muscle from Northern Norway

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Abstract
Water and protein contents of muscle and gonad index of sexually mature and immature cod of the same size were studied throughout a one‐year cycle. In mature cod, the gonad was found to increase isometrically with fish weight suggesting that the relative energy demand for gonadal growth is independent of fish size. Spawning took place in late March or early April. Similar seasonal variations of water and protein contents of the muscle occurred in both mature and immature cod. In December to February, the protein content reached a maximum and water content a minimum, and in March to April, protein content was low, whereas the water content of the muscle was at a maximum. Since mature and immature cod showed the same variations in body composition, it is suggested that little of the seasonal variations of mature cod can be explained by reproductive processes.