The influence of dietary lipid inclusion and daily ration on growth and smoltification in 1+ Atlantic salmon (Salmo salar) parr

Abstract

The effects of diet regime on growth and smoltification in 1+ Atlantic salmon parr were studied. Two groups of approximately 400 salmon parr, in triplicate, were fed diets containing either 25% or 12.5% lipid from first-feeding. Two further treatments were fed either the 25% or 12.5% lipid diet for 98 days, after which they were fed the alternate diet. In a second experiment three groups of 550 parr, in duplicate, were fed at full, two-thirds or one-third of the manufacturers’ recommended ration, from first-feeding. All groups were maintained on their respective diet regimes until smoltification approximately one year after first-feeding. In experiment 1, lipid level had a significant effect on whole body lipid content. However growth and the incidence of smoltification was not affected by dietary lipid inclusion, with upper modal group fish from each treatment achieving a similar smolt status (in terms of condition factor and Na+, K+-ATPase) at seawater transfer. In experiment 2, growth and the incidence of smolt transformation increased with ration. Full and two-thirds ration fish maintained similar body lipid contents throughout the experiment, with that of the one-third ration fish lower only during early development, indicating that growth was controlled by the maintenance of a distinct lipid level. It is concluded that ration, and not dietary lipid inclusion, has a significant effect on growth and the decision to undergo smoltification in salmon parr.