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

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 1 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 were not affected by dietary lipid inclusion, with the upper modal group (UMG) fish from each treatment achieving a similar smolt status (in terms of condition factor [CF] 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 the 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. © 2004 Elsevier B.V. All rights reserved.