Effect of temporary reductions in feeding on protein synthesis and energy storage of juvenile Atlantic salmon

Abstract

Biochemical and tissue‐composition indices were used to determine the impacts of temporary feeding reductions on juvenile Atlantic salmon (4.2g initial weight). Three levels of food reduction (fasting, 20% of control, 50% of control) lasting for 2, 4 or 8 days were compared to a control group (constant feeding at 2.75% of body weight day−1). Ornithine decarboxylase (ODC) activity and RNA concentrations were used to measure changes in protein synthesis; condition factor (K), liver‐somatic index (LSI), visceral‐somatic index (VSI), and gut index (GI)were used to provide information on stored energy levels. Results showed that physiological adjustments to decreases or increases in feeding occur very quickly. The most rapid responses were changes in ODC activity (within 2 days) and LSI (2–4 days). Changes in RNA concentrations and K required 4–8 days. There was no apparent effect of the treatments on VSI or GI. Temporary reductions of feeding lasting 2 days or less would not be detected by any index except ODC activity. Changes in the indices are discussed with respect to short‐term changes in rates of protein synthesis and energy storage.