Effects of seasonal temperature and photoperiod on Atlantic cod (Gadus morhua). I. Morphometric parameters and metabolites

Age-1+ to age-3+ Atlantic cod (Gadus morhua) were held at either constant (∼9°C) or ambient ocean temperatures (Newfoundland) from December 2000 to June 2002 under natural photoperiod and ad libitum feeding. Body mass and length, liver total lipids, triacylglycerols and free fatty acids, glycogen and protein from liver and muscle, plasma glucose, and lactate were assessed over this period. Both groups increased body mass, length, and liver mass, with a significantly greater increase for the constant group at all sampling dates. Both groups demonstrated a growth phase from August to October 2001, while the ambient group showed a compensatory growth phase from May to July 2001. Gonad mass significantly increased in males and females from both groups in June 2002. Most tissue metabolites demonstrated seasonal patterns consistent with photoperiod. The effect of temperature was primarily quantitative, implicating temperature changes food conversion efficiencies, as both groups of cod had the same access to food. Under the conditions of this study, Atlantic cod growth is controlled primarily by photoperiod, with temperature affecting the amounts of tissue metabolites.