The effects of starvation and sexual maturation on Na+ transbranchial fluxes following direct transfer from fresh water to sea-water in rainbow trout (Salmo gairdneri).

1. The perfused isolated head technique has been used to measure sodium arterial fluxes following direct transfer from fresh water to sea-water. 2. A starvation-related decrease in net sodium flux is reported. 3. Sexual maturation slackens the decrement of this net flux. 4. In starved fish, the cytological modifications of chloride cells following such a transfer are delayed. 5. This effect of starvation is discussed in terms of lamella sodium imperviousness.