EFFECTS OF INTERMEDIATE AND LOW-SALINITY CONDITIONS ON GROWTH-RATE AND FOOD CONVERSION OF ATLANTIC COD (GADUS-MORHUA)

Growth rates of Atlantic cod (Gadus morhua) were measured under different salinity conditions to test the hypothesis that growth would be best in an isosmotic environment. The results of two experiments (spring and autumn 1991) conducted at three different salinities (7, 14, and 28 parts per thousand) and two feeding regimes indicate a significant effect of salinity and ration on growth rate. Within each experiment, growth rates were highest for cod maintained in intermediate salinity conditions (14 parts per thousand). Growth rates in low salinity conditions (7 parts per thousand) were higher than in seawater (28 parts per thousand) during the spring, but during the autumn, growth rates of cod held under low salinity conditions and in seawater were similar. Higher growth rates at lower salinities resulted from an increase in food conversion efficiency. They were not associated with an increase in food intake, changes in composition (proteins, lipids, or water), or relative allocation of energy to the tissues (muscle, liver, and gonads) of cod. The results indicate that rearing cod at intermediate salinities, such as would occur in estuaries or coastal regions, could confer an advantage for cod aquaculture.