The effect of orally administered 3,5,3′-triiodo-L-thyronine on growth and salinity tolerance of Atlantic salmon ( Salmo salar L.)

Abstract

Atlantic salmon ( Salmo salar) juveniles were fed diets containing 0, 10, 20 and 100 ppm 3,5,3′-triiodo-L-thyronine (T 3) to test the effect of this hormone on growth, salinity tolerance and smoltification. Two 6-month feeding experiments, beginning in summer (experiment A) and winter (experiment B), were conducted under simulated natural photoperiods and temperatures. In each experiment, T 3-supplemented diets significantly elevated plasma T 3 levels and growth rates in a dose-dependent manner. T 3 administration increased relative opercular and fin growth, resulting in severe morphological abnormalities at the highest dose. The proportion of precociously mature males in experiment A was decreased by T 3 treatment. T 3 treatment significantly increased salinity tolerance in mature males but not in immature fish. In fish acclimated to sea water in spring (experiment B), T 3 treatment increased seawater survival for the first 2 months, but had no effect thereafter. T 3 did not change lipid content, moisture content or gill Na +K +-ATPase activity in fresh water. We conclude that, while T 3 supplemented diets are effective in promoting growth, there was no demonstrable direct effect on smoltification.