Abstract
The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.
Highlights
As the freshwater species with the northernmost distribution in the world, the Arctic charr (Salvelinus alpinus) experiences large variations in day length throughout the year
Siikavuopio, Sæther, Skybakmoen, Uhlig, and Haugland (2009) confirmed those findings when Arctic charr, reared under continuous light conditions, were exposed to a period of short day length during winter and responded with a growth increase resulting in a 25% higher weight gain compared with that of fish reared at continuous light for the whole period
In a long-term study, Siikavuopio et al (2009) reported a 25%–30% higher growth rate of wild Arctic charr held under culture condition and exposed to intervals of short day length in between periods of continuous light compared with a group reared at continuous light
Summary
As the freshwater species with the northernmost distribution in the world, the Arctic charr (Salvelinus alpinus) experiences large variations in day length throughout the year. Siikavuopio, Sæther, Skybakmoen, Uhlig, and Haugland (2009) confirmed those findings when Arctic charr, reared under continuous light conditions, were exposed to a period of short day length during winter and responded with a growth increase resulting in a 25% higher weight gain compared with that of fish reared at continuous light for the whole period. The potential effect these photoperiod regimes had on subsequent maturation of the fish was, not investigated. The experiment lasted from 21 April 2009 to 20 October 2010 (18 months)
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