Seasonal changes in food consumption and growth of Arctic charr exposed to either simulated natural or a 12:12 LD photoperiod at constant water temperature

Immature male and female and maturing male Arctic charr Salvelinus alpinus were held at constant temperature (4° C) under either simulated natural photoperiod (nLD) or constant photoperiod (12:12 LD) conditions, and feed intake and growth were monitored at monthly intervals over 13 months. Food was supplied in excess during a 5-h period each day, and daily consumption was determined using X-radiography. Food consumption and growth of both immature and maturing fish showed distinct seasonal cycles irrespective of photoperiod treatment. Feed intake and growth rates were highest in mid-summer and lowest in autumn. The fact that seasonal cycles persisted under constant photoperiod (12:12 LD) and temperature conditions suggests that circannual rhythms of food consumption and growth exist in the absence of seasonal changes in these environmental cues. The data support the view that seasonal changes in food consumption and growth in the Arctic charr are driven by endogenous rhythms. Reductions in feeding and growth in autumn occurred about 1 month earlier in the maturing males than in the immature fish. Males that matured under the 12:12 LD regime displayed a growth cycle that was delayed in comparison with that shown by the maturing males held under nLD.