The effect of salinity on desmoltification in Atlantic salmon

Abstract

In order to determine which salinity is needed to prevent desmoltification in Atlantic salmon, Salmo salar, changes in the hypoosmoregulatory capacity of postsmolts reared at different salinities were monitored. Smolting occurred under natural light and temperature conditions, and was completed by mid-June. Thereafter the smolts were divided into six groups reared at different salinities (0, 10, 15, 21, 26 and 31‰). The hypoosmoregulatory capacity was measured by 24 h seawater challenge tests. A decrease in hypoosmoregulatory capacity was evident in the groups kept at 0 and 10‰, and 3 weeks after smolting there was a significant difference between the 0‰ group and the groups kept on 15‰ or higher. Two weeks later both the 0‰ and the 10‰ groups had regained a high hypoosmoregulatory capacity, indicating that desmoltification did not result in a lasting state of low hypoosmoregulatory capacity, but rather appeared as a transient process lasting no more than 5–6 weeks.