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Effects of an advanced temperature cycle on smolt development and endocrinology indicate that temperature is not a zeitgeber for smolting in Atlantic salmon

Stephen D. McCormick^1,*, J. Mark Shrimpton^1,, Shunsuke Moriyama² and Björn Thrandur Björnsson³

¹ USGS, Leetown Science Center, Conte Anadromous Fish Research Center, Turners Falls, MA 01376, USA
² Laboratory of Molecular Endocrinology, School of Fisheries, Kitasato University, Sanriku, Iwate, Japan
³ Fish Endocrinology Laboratory, Department of Zoology, Göteborg University, Göteborg, Sweden
Present address: Biology Program, University of Northern British Columbia, Prince George, British Columbia, Canada, V2N 4Z9

View larger version (19K): [in a new window]   Fig. 1. (A) Seasonal change in temperature and daylength of the four experimental groups. Temperature increases in the advanced temperature group (ADV) began on February 14 (arrowhead). (B) Length (cm) and (C) condition factor (massxlength-3)x100 in juvenile Atlantic salmon subjected to different photoperiod and temperature treatments. Values are means ± S.E.M. (N=12). There were significant effects of photoperiod, temperature and time on condition factor, and significant effects of temperature and time on length (P<0.05, three-way ANOVA). Vertical lines unconnected to other lines indicate a significant difference from other groups at that time; points without vertical lines are not significantly different from one another (P>0.05, Kruskal-Wallis test).

View larger version (20K): [in a new window]   Fig. 2. Gill Na+,K+-ATPase activity (µmol ADP mg-1 protein h-1) (A), plasma growth hormone levels (GH, ng ml-1; B) and insulin-like growth factor I levels (IGF-I, ng ml-1; C) in juvenile Atlantic salmon subjected to different temperature and photoperiod treatments (see Fig. 1). Values are means ± S.E.M. (N=12). Temperature increases in the advanced temperature group began on February 14 (arrowhead). There were significant effects of photoperiod, temperature and time on gill Na+,K+-ATPase activity and plasma IGF-I levels, and significant effects of photoperiod and time on plasma GH levels (P<0.05, three-way ANOVA). Vertical lines unconnected to other lines indicate a significant difference from other groups at that time point; time points with no vertical lines are not significantly different from one another (P=0.05, Kruskal-Wallis test).

View larger version (20K): [in a new window]   Fig. 3. Plasma thyroxine (T4, ng ml-1; A), triiodothyronine (T3, ng ml-1; B) and cortisol (ng ml-1; C) levels in juvenile Atlantic salmon subjected to different temperature and photoperiod treatments (see Fig. 1). Values are means ± S.E.M. (N=12). Temperature increases in the advanced temperature group began on February 14 (arrowhead). There were significant effects of photoperiod, temperature and time on plasma T4 and T3 levels (P<0.05, three-way ANOVA). There was a significant effect of time on plasma cortisol and a significant interaction between time, photoperiod and temperature (P<0.05, three-way ANOVA). Vertical lines unconnected to other lines indicate a significant difference from other groups at that time; points without vertical lines are not significantly different from one another (P=0.05, Kruskal-Wallis test).