Parr-smolt transformation in nonanadromous Atlantic salmon Salmo salar and effects of sexual maturation on the parr-smolt transformation in male anadromous Atlantic salmon

The parr-smolt transformation was compared in male and female anadromous (SRxSR), nonanadromous (LLxLL) and hybrid (SRxLL) Atlantic salmon, Salmo salar. Seasonal patterns in total lipid content, moisture content, condition factor, silvering, and branchial Na+-K+ ATPase activity indicate that smoltification occurred in immature SRxSR females while previously mature SRxSR males did not smoltify. It was also apparent that, in general, smoltification was not completed in either sex of the SRxLL or LLxLL salmon. Histological examination of gill tissue revealed that chloride cells appeared to decline in number over the summer in fish retained in freshwater, whereas seawater acclimated fish, at this time, had numerous well developed chloride cells. -- Wild anadromous smolts of the Exploits River stock had high branchial Na+-K+ ATPase activity and adapted to seawater without marked elevation of plasma sodium or chloride1 ion concentration. Mortality was high in LLxLL salmon during the course of exposure to seawater and the group exhibited elevated plasma ion concentrations. Induction of branchial Na+-K+ ATPase activity did not appear to lower plasma ion concentrations in LLxLL salmon exposed to seawater. It appears that genetic differences in smolting patterns occur in mature male salmon from anadromous populations. As well, differences appear to exist in adaptability to seawater among stocks of nonanadromous Atlantic salmon. Differences in smoltification patterns in anadromous and nod anadromous salmon are discussed in terms of the evolution of the different life history patterns observed in the two forms.