Preventing sexual maturation in Arctic charr by 24h light overwinter and suppressing somatic growth

To address the problem of high maturity at 2years of age among Salvelinus alpinus (Labrador strain), PIT-tagged yearlings (ca. 110g) were reared for 18weeks overwinter (Nov. 16 to Apr. 1) under six treatments (90 fish per treatment) that combined three factors: photoperiod (natural day length, LDN or 24h light, LL), temperature (10 or 5°C), and food (fed daily or no food). On April 1 all fish were returned to LDN, 10°C and fed daily for a further six months. In November, the maturity rate was very high among fish reared the previous winter under LDN and fed daily at both 10°C (♀ 94%, ♂ 43%) and 5°C (♀ 87%, ♂ 45%). Replacing LDN with LL overwinter, at 10°C halved the maturity rate (♀ 49%, ♂ 19%), and at 5°C eliminated maturity among females, and male maturity was 6%. Food deprivation for 18weeks posed no health problems, and combined with LL also was highly effective at preventing maturation, both at 10°C (♀ 0%, ♂ 2%) and 5°C (♀ 0%, ♂ 7%). Compensatory growth following the suppression of growth overwinter indicates this approach to reducing maturity can be a commercially viable means to produce 1kg immature product around 2years old. A new two-step gating mechanism is proposed to explain the photoperiod prevention of maturation, one independent of somatic growth, the other dependent. This study shows that the combination of LL, reduced temperature and food deprivation can significantly reduce the incidence of maturation and improve the productivity among diploid Arctic charr. This combination approach can potentially be applied to other farmed salmonids and non-salmonids to improve the efficacy of controlling sexual maturation. •The ability to reduce the problem of early maturity using 24h light was maximized when combined with reduced temperature and food restriction.•Combined food deprivation with 24h light overwinter can be a cost-effective method for farming Arctic charr and potentially other species.•A two-step gating mechanism was proposed to explain the photoperiod controlled sexual maturation, one independent of growth, the other dependent.