Compensatory growth response of juvenile Arctic charr (Salvelinus alpinus L. Nauyuk) under various cyclical food restriction and refeeding periods.

Abstract

Overwinter feed restriction followed by spring refeeding is proposed as a strategy to improve productivity and sustainability of Arctic charr production. A 257-day experiment was conducted with different feeding regimes to evaluate compensatory growth response in growth and physiological state of juvenile fish (150-200 g) reared under seasonal temperature and photoperiod. Five experimental groups in replicates were created based on frequency (C = continuous and P = periodic) and feed restriction level (0, 50 and 100%): C100%, P50%, C50%, P0% and C0%. After a period of acclimation of one month, two distinct phases of the growth trial were conceived: a restriction period (102 days) followed by a refeeding period (126 days). The growth (SGR's, organ indexes (HSI, CSI, ISI and VSI), FCE and FI) and pyloric caeca digestive (TRYP, CHY) and metabolic (LDH and CS) enzyme activity, stress levels (cortisol, HSP70 and hematocrit), morphometric traits (body mass, length and K) and muscle proximate composition were evaluated at different intervals. Our results indicate that 1) a limited period of food restriction (P0%) or a prolonged starving (C0%) enabled the observation of a complete growth compensation after 86 and 126 days post-refeeding respectively with improved feed conversion efficiency (FCE of 1.20 for P0% and C0% compared to 1.06 for the control); 2) Arctic charr under a fair level of food reduction applied either periodically (P50%) or continuously (C50%) can achieve similar growth than un-restricted fish; 3) during the refeeding period, lower variability in growth was successfully induced (C100% > P50% > C50% > P0% > C0%); 4) rapid size or mass adjustment of key digestive organs such as pyloric caeca and intestine is associated with feed restriction and refeeding (reduction and increase in relative size respectively); 5) enzymatic activities of TRY, LDH and CS measured at the last sampling of the restriction phase indicate some level of adjustments that quickly receded to levels similar to the control group (9 days post-refeeding); 6) lipid content value was significantly higher in fish from the C100% group in comparison to C50%, P0% and C0% groups at the end of the restriction phase, indicating that lipid depletion is a prerequisite to compensatory growth induction and 7) in comparison to the control un-restricted fish, the stress levels, as estimated by stress markers (cortisol, HSP70 or hematocrit) were not affected by the level of feed restriction. Feed restriction has been successfully used to promote compensatory and catch-up growth. Here we suggest that studies are however required to further explore to which extent feed-restriction could induce vulnerability of Arctic charr, during sub-optimal growth conditions. Finally, defining the best sequence of feed restriction and refeeding should ensure implementation of production and benefit while maintaining optimal health conditions.