Sexual maturation and smoltification in domesticated Atlantic salmon (Salmo salar L.) – is there a developmental conflict?

We present data from two experiments that examined how the developmental processes of smoltification and sexual maturation proceed in parallel in domesticated Atlantic salmon. Onset of maturation and smoltification was stimulated using temperature and photoperiod. Our observations on gonadosomatic index (GSI), spermatogenic activity, gill Na+, K+‐ATPase enzyme (NKA) activity, and plasma 11‐ketotestosterone (11‐KT), Na, Cl, and Ca show that smoltification and maturation were both triggered and developed in parallel in male Atlantic salmon, but that the progressing maturation impaired hypoosmoregulation. Female maturation started after completion of smoltification. Furthermore, we present data showing that domesticated salmon can physiologically smoltify–desmoltify–resmoltify within a short period of time, and that development of a secondary sexual characteristic, such as a kype, depends on size in male postsmolts. The study shows that smoltification and maturation can develop in parallel and without conflicting in male Atlantic salmon. However, with time, maturation impaired hypoosmoregulation. Moreover, physiological smoltification–desmoltification–resmoltification were observed within a short time period, showing the plasticity and robustness of the osmoregulatory system in domesticated salmon.