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 differ ent salinity conditions to test the hypothesis that growth would be be st 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 condi tions (7 parts per thousand) were higher than in seawater (28 parts pe r thousand) during the spring, but during the autumn, growth rates of cod held under low salinity conditions and in seawater were similar. H igher growth rates at lower salinities resulted from an increase in fo od 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 gonad s) of cod. The results indicate that rearing cod at intermediate salin ities, such as would occur in estuaries or coastal regions, could conf er an advantage for cod aquaculture.