Effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters of juvenile Atlantic cod (Gadus morhua)

The effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters were investigated in two experiments. In the first experiment small, medium and large juvenile Atlantic cod Gadus morhua (initial average weights of 1.9, 8 and 83 g, respectively) were reared at four constant salinities (6 to 32 parts per thousand) for a short period (19-57 days, depending on size), then returned to seawater (32 parts per thousand) without acclimation and reared for another period (20-391 days). The highest growth rates were found at 10 parts per thousand in all size-classes. After the fish were returned to seawater the growth rates were inversely related to the salinity change in all size-classes and long-term rearing of the medium-sized fish revealed that abrupt salinity increase from 6 and 10 parts per thousand to seawater may permanently reduce the growth capacity of juvenile cod. In another long-term experiment, there was no significant difference in the growth rate of cod (initial average weight 3.4 g) reared at either 13.5 or 32 parts per thousand for 187 days. Rearing at 13.5 parts per thousand neither enhanced growth rate at 6.3 degrees C nor at 10 degrees C in larger juveniles (>245 g) compared with rearing in seawater. The study shows that rearing salinity and abrupt salinity changes have limited or no effects on stress and immune-related parameters, and there are no indications of ion regulatory disturbances at salinities as low as 6 parts per thousand. This shows that the Atlantic cod is an extremely euryhaline marine teleost species, and indicates that commercial Atlantic cod aquaculture can just as well be carried out in locations with low as with high environmental salinity. (C) 2012 Published by Elsevier B.V.