Temperature influence on the development and loss of seawater tolerance in two fast-growing strains of Atlantic salmon

Development of hypo-osmoregulatory ability, gill Na,K-ATPase activity, condition factor and growth in Atlantic salmon during parr–smolt transformation was studied in a 2 3 factorial design with three temperatures (12.0, 8.9 jC and ambient, 2.4–11.9 jC, mean: 6.0 jC) and two farmed strains of smolts (Mowi and AquaGen). The development of hypo-osmoregulatory ability and gill Na,K-ATPase activity were significantly influenced by freshwater temperature. In smolts raised at 12.0 jC, maximum gill Na,K-ATPase activity was reached in late April, compared with late May and mid-June in the 8.9 jC and ambient groups, respectively. In all groups, peak gill Na,K-ATPase activity was seen 350 degree days (d jC) after the onset of the smolt-related increase in enzyme activity (30 March) The period of high enzyme activity (>90% of maximum) lasted approximately 250 d jC. No distinct peak level in gill Na,KATPase activity was seen in the AquaGen strain at ambient temperature. Elevated temperatures also accelerated the loss of hypo-osmoregulatory capacity. In all groups, gill Na,K-ATPase activity reached pre-smolt levels approximately 500 d jC after the calculated peak level. Growth rate in freshwater was influenced by strain, temperature and their interaction, with the Mowi strain showing a higher growth rate than the AquaGen strain at 8.9 jC and ambient temperatures. Following transfer to seawater, a higher growth rate was recorded in smolts from the Mowi strain than the AquaGen strain from the ambient temperature regime. Temperature 0044-8486/$ see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2003.08.028 * Corresponding author. Tel.: +47-55-58-45-45; fax: +47-55-58-44-50. E-mail address: [email protected] (S.O. Handeland). S.O. Handeland et al. / Aquaculture 233 (2004) 513–529 514 influences the development and loss of smolt characteristics in both strains, and has long-term effects on post-smolt performance in seawater. D 2004 Elsevier B.V. All rights reserved.