Reduced photoperiod (18 h light vs 24 h light) during first-year rearing associated with increased early male maturation in Atlantic salmon Salmo salar cultured in a freshwater recirculation aquaculture system

Authors: GOOD, CHRISTOPHER - Freshwater Institute; Weber, Gregory - Greg; MAY, TRAVIS - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2015
Publication Date: 3/18/2015
Publication URL: https://handle.nal.usda.gov/10113/61090
Citation: Good, C., Weber, G.M., May, T., Davidson, J., Summerfelt, S. 2015. Reduced photoperiod (18 h light vs 24 h light) during first-year rearing associated with increased early male maturation in Atlantic salmon Salmo salar cultured in a freshwater recirculation aquaculture system. Aquaculture Research. DOI: 10.1111/are.12741.

Interpretive Summary: Many environmental factors influence the onset of sexual maturation in Atlantic salmon, including photoperiod (or change thereof). Because maturation is undesirable in salmon production, due to reduced feed efficiency, fillet yield, and product quality, we sought to examine two photoperiod regimes (24h light, vs. 18h light / 6h dark) applied during first-year rearing in order to assess maturation rates during second-year growout under 24h photoperiod. Based on plasma 11-ketotestosterone (the major fish androgen) concentrations, and morphologic assessments (i.e. gonadosomatic indices), we determined that the reduced photoperiod was associated with significantly higher levels of male maturation during growout to market size, and therefore there appears to be no advantage to reduced photoperiod in this regard. However, male maturation was still prevalent in the full photoperiod group, and therefore further research is required to identify and control key environmental variables associated with precocious maturation.

Technical Abstract: Early male sexual maturation in Atlantic salmon Salmo salar is undesirable for a number of reasons related to production efficiency, and it appears that precocious maturation is a particular problem when raising this species to market size in water recirculation aquaculture systems (RAS). We investigated whether a reduced (18h light : 16h dark) photoperiod, versus a full (24h light) photoperiod, provided during first year rearing, was associated with reduced early maturation during second year growout in a semi-commercial scale freshwater RAS. We assessed maturation in male salmon during four sampling events over the second year of growout by quantifying plasma 11-ketotestosterone (11-KT), gonadosomatic indices (GSI), and estimated grilse prevalence based on GSI and physical characteristics. Overall, we found that a reduced first year photoperiod was actually associated with a significantly increased level of maturation during growout, based on the majority of assessments carried out. Plasma 11-KT concentrations in the 18h:6h group were significantly higher at 19- and 24-months post-hatch in this group; likewise, mean GSI values were significantly higher in the 18h:6h treatment group at 19- and 24-months post-hatch. Although grilse were observed in both treatment groups during the 16-, 19-, and 24-month sampling events, the odds of grilse being from the 18h:6h treatment group were significantly higher at 16- and 24-months post-hatch. Our results demonstrate that, under the conditions of this study, reducing photoperiod during the first year was associated with increased male maturation during the second year of growout.