Liu, Qi2019-11-202019-11-202019-11-20http://hdl.handle.net/10222/76636Farming diploid Arctic charr (Salvelinus alpinus; Labrador strain) in Atlantic Canada is greatly impeded by unwanted sexual maturation and associated loss of growth and meat quality. Up to 70% of fish in both sexes mature at age 2, due to accelerated growth from both a high energy diet and rearing in ‘warm’ 10°C well water. The goal to reduce maturity to <20% was achieved by manipulating photoperiod, rearing temperature and feeding in a series of five lab-based trials each lasting 12-18 months ending age 2. To explore the relationship between somatic growth and the physiological decision to mature, all fish were identified with a PIT-tag and measured monthly. Continuous light (LL) overwinter effectively reduced maturation. Histological analysis of germ cells revealed the change between natural daylength (LDN) and LL induced a dichotomous response, stimulating some fish and inhibiting others, dependent on the direction and timing of photoperiod change. Food deprivation and/or 5°C overwinter alone were less effective than LL at reducing maturation, but combining all three factors reduced maturity to <5%. Paradoxically, body weight, condition factor and lipid content were poor indicators of whether an individual would mature or not. Plasma melatonin monitoring indicated 50 lux at night was a sufficient intensity for effective LL treatment. Charr failed to exhibit a circannual rhythm of sexual maturation under LL and LD 8:16 suggesting the conventional thinking on the mechanism by which photoperiod controls sexual maturation among salmonids requires further investigation.enAge at MaturitySalmonidPhotoperiod and Growth Manipulation Reduces the Problem of Unwanted Sexual Maturation in Arctic Charr, Salvelinus alpinus