Effects of photoperiod and temperature on growth and parr-smolt transformation in Atlantic salmon ( Salmo salar L.) and subsequent performance in seawater

Abstract

Potential Atlantic salmon ( Salmo salar L.) 1 + smolts were reared during late winter and spring in a factorial design combining elevated, 12–13°C ( e), or ambient ( a) temperature with four photoperiod regimes: simulated natural photoperiod, 60°N (LN60, control); simulated natural photoperiod, 70°N (LN70); simulated natural photoperiod, 1 month phase delayed (LD60); and continuous light (LL). Growth rate in fresh water was enhanced by elevated water temperature and continuous light. No consistent differences were seen among the LN70 and LN60 groups at the two temperature regimes, whereas the LD60 e group had a lower growth rate than LN60 e. Condition factor decreased between February and April on LL under both thermal regimes. For the other groups on elevated temperature, condition factor decreased from March onwards, while no clear reduction was seen among the LN60 a, LN70 a or LD60 a groups. Based on morphological changes, increase in hypo-osmoregulatory ability and gill Na +,K +-ATPase activity, the LN60 e, LN70 e and LD60 e groups developed smolt characters in April or early May, while corresponding groups on ambient temperature did not complete smoltification until late May or early June. Fish were transferred to seawater in mid-June and measured again in mid-November. Groups reared on ambient temperature had higher growth rates in seawater than corresponding groups from elevated temperature. Smolts from LD60 had lower growth rate than did those from LN60 and LN70, indicating that the delay in photoperiod influenced the completion and/or timing of smolting. The LL e group had the lowest growth rate in seawater, suggesting that the continued exposure to LL and elevated temperature interfered with the normal course of parr-smolt transformation.