Long photoperiod in winter is more effective than food deprivation in stopping unwanted sexual maturation in Arctic charr

Yearling Salvelinus alpinus (ca. 30 g body weight) at constant 10 °C were subjected to one of four food deprivation regimes: Fall (7 weeks no food: Oct. 10 to Nov. 30), Winter (8 weeks: Dec. 1 to Jan. 31), Fall + Winter (15 weeks, Oct. 10 to Jan. 31) or fed to satiation daily (control). Each feeding regime was sub-divided between three photoperiod treatments (n = 70 fish/trt.) each lasting 15 weeks (Oct. 10 to Feb. 1): either 24 h light (LL), 18 h light:6 h dark (LD 18:6) or simulated natural daylength (LDN). On Feb. 1, all fish were returned to daily feeding and LDN for a further 8 months. The incidence of maturation in October age 2 was reduced seven-fold to <6%, (sexes pooled) by both LL and LD 18:6 overwinter compared to 43% in the control (LDN and daily feeding), independent of the feeding regime. Fall + Winter food deprivation under LDN reduced female maturity six-fold to 11%, but male maturity was unaffected (♂:27%). Food deprivation under LDN in fall had no significant effect on maturation (♀:52%; ♂:42%) but in winter was more effective, significantly reducing maturity in both sexes (♀:32%; ♂:15%). The changes in mean body weight and condition factor between incipient maturing and immature charr within treatments through fall and winter were similar. From March onwards, however, mean condition factor decreased significantly following the decrease in photoperiod from LL or LD 18:6 to LDN associated with a low incidence of maturation age 2. Neither food deprivation nor LL raised welfare concerns based on survival, behavior and growth, and the reduction in the maturity was a health benefit.