Photoperiod and Growth Manipulation Reduces the Problem of Unwanted Sexual Maturation in Arctic Charr, Salvelinus alpinus

• Main Author: Liu, Qi
• Other Authors: Department of Biology, Doctor of Philosophy, Dr. Tillmann Benfey, Dr. Sophia Stone, Dr. Tony Manning, Dr. Christophe Herbinger, Dr. Leslie MacLaren, Dr. James Duston, Received, Yes, No
• Language: English
• Published: 2019
• Subjects: Age at Maturity; Salmonid; Arctic; Canada; Arctic charr; Salvelinus alpinus
• Online Access: http://hdl.handle.net/10222/76636

Farming 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.