Long‐term rearing of Arctic charr Salvelinus alpinus under different salinity regimes at constant temperature

Abstract

Arctic charr Salvelinus alpinus of the Hólar strain (mean ± s.e. body mass = 152·1 ± 3·1 g) were reared at four different salinity regimes at a constant temperature of 7·4° C. Two groups were given a three-month acclimation in salinity 18 before the salinity was increased to either 25 or 29 (groups called A25 and A29), and two groups were reared in salinities 25 or 29 over the full experimental period of 409 days (groups called F25 and F29). In the first 3 months, the A25 and A29 groups had the highest growth rates. By October 2011, there were no significant differences (two-way nested ANOVA, P > 0·05) in the mean body masses among A25, F25 and F29 (c. 1450 g), whereas A29 had a lower mean mass (1282 g). The growth in the last period from October 2011 to January 2012 was reduced by sexual maturation in the highest salinity regimes (A29 and F29), whereas fish in groups A25 and F25 showed high growth throughout the study. Males in all salinity groups had higher growth rates than females for the most part of the study, but the divergence between the sexes was most pronounced in the highest salinity regimes. All salinity groups showed distinct changes in Na(+) , K(+) -ATPase activity, with high activity in spring and summer, and lower activity in the autumn. Plasma sodium (Na(+) ) levels were stable indicating that none of the experimental groups had problems in maintaining hydromineral balance during the study. While plasma leptin levels were not affected by salinity regimes, it was noted that these levels were 13-30% higher in fish with empty guts compared with those having food in their gut at the time of sampling. This suggests a link between leptin levels and food intake, indicating that this hormone may play a role in food intake and energy allocation in fishes.

Effects of short‐day treatment on long‐term growth performance and maturation of farmed Arctic charr Salvelinus alpinus reared in brackish water

“…Also, it is known that short‐term (hours, days) changes in leptin levels occur in fishes (Fuentes et al , ). No correlation between plasma leptin levels and condition factor was found in this study, in line with results from Árnason et al () working with S . alpinus .…”

“…In this study, the females kept at lower salinities had higher growth rate from October onwards while I G levels for the same group were lower in May and August. Árnason et al () reported similar effect from rearing salinity on gonadal growth of S . alpinus .…”

“…The observed trend towards lower growth at higher rearing salinity is in agreement with results from previous studies on growth rates of S . alpinus at elevated salinities (Mortensen & Lund, ; Duston et al , ; Árnason et al , ). Higher growth at lower salinities found in this study may be linked to higher consumption of feed compared to fish reared at 27 salinity.…”

“…There are no previous reports on the photoperiod effect on development of osmoregulatory ability in the Holar strain used in this study (farmed strain that has been selectively bred for several seasons). Working with the Hólar strain, however, Árnason et al () reported that for S . alpinus reared at constant light but 3·7 salinity from start feeding until attaining an average size of c .…”

Impact of environmental factors on the growth and maturation of farmed Arctic charr

“…In another study, Gunnarsson et al (2014) found that Arctic charr maintain high NKA activity and relatively stable levels of plasma Na + at 27 ppt, although growth rate was lower at 27 ppt than at 17 ppt. Similarly, Arnason et al (2014) reported lower long-term growth at 29 ppt than at 25 ppt. Due to the limited and seasonal seawater tolerance (Finstad et al 1989;Arnesen et al 1993a, b), most of the production of Arctic charr (on-growing) takes place either in freshwater or in brackish water.…”