The use of continuous light to suppress pre-harvest sexual maturation in sea-reared Atlantic salmon (Salmo salar L.) can be reduced to a four month window

Abstract

In Atlantic salmon Salmo salar L. sexual maturation is concomitant with a redistribution of the somatic resources and the development of nuptial colouration responsible for the low commercial value of mature fish (Michie, 2001). Maturing fish also exhibit an altered feeding activity (Kadri et al., 1996; Kadri et al., 1997a and b) and increased pathogen susceptibility (Bruno, 1989; St-Hilaire et al., 1998; Currie and Woo, 2007) likely to compromise growth, health and welfare of the cohabiting immature cohort. The suppression of pre-harvest sexual maturation is therefore a priority in the salmon on-growing industry and is achieved by photoperiodic manipulation of the stock in the form of continuous artificial-light (LL) applied between the winter and summer solstice during the second year at sea. This 6-month period LL-regime is recognized as the most efficient by providing a key environmental signal that phase-advances the so-called “spring decision window” such that a reduced proportion of the stock meets the developmental/energetic thresholds required to proceed through maturation (Taranger et al., 1998; Endal et al., 2000; Oppedal et al., 2006). Current knowledge on the photoperiodic entrainment of reproduction in Atlantic salmon suggests that terminating LL-exposure before the summer solstice could be equally efficient at suppressing sexual maturation. This study tested this hypothesis on a commercial scale with the objective of reducing energy usage and potential welfare impacts associated with the long-term use of powerful lighting systems in sea-pens (Migaud et al., 2007a).