Can Atlantic salmon smolt twice? Endocrine and biochemical changes during smolting

• Main Authors: J. Mark Shrimpton, Björn Thr, Ur Björnsson, Stephen D. Mccormick
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2000
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.418.9163; http://www.bio.umass.edu/biology/mccormick/pdf/cjfas smolt twice.pdf

Abstract: Smolting is characterized by morphological and physiological changes, some of which are reversible if fish remain in freshwater. Whether fish that smolt in the first year will repeat physiological changes associated with smolting a second time is not known. To assess whether Atlantic salmon (Salmo salar) can smolt more than once, we sampled hatchery-reared Atlantic salmon at monthly intervals for 2 years beginning the fall after hatching. Fish showed differences in rate of growth and were easily differentiated by size into upper mode (UM) and lower mode (LM) by the first fall. In the first spring, gill Na +,K +-ATPase activity of UM and LM fish increased six- and three-fold, respectively. Plasma growth hormone levels in spring were significantly elevated in UM fish but not in LM. Plasma cortisol levels changed little and gill corticosteroid receptor concentration did not differ between the groups. During the summer, gill Na +,K +-ATPase activity declined in both groups and remained low until the next spring. The second spring, growth hormone levels did not increase significantly and cortisol levels increased. The increase in gill Na +,K +-ATPase activity and cortisol and high saltwater tolerance indicate that UM Atlantic salmon can smolt in two consecutive years. Résumé: La smoltification se caractérise par des changements morphologiques et physiologiques dont certains sont réversibles si les poissons restent en eau douce. Nous ne savons pas si les poissons qui smoltifient la première année vont reproduire une deuxième fois les changements physiologiques associés à la smoltification. Pour déterminer si le saumon atlantique peut subir plus d’une smoltification, nous avons échantillonné des saumons d’élevage à intervalle