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Marine Ecology Progress Series

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MEPS 221:245-253 (2001)  -  doi:10.3354/meps221245

Timing of Atlantic cod Gadus morhua seasonal migrations in relation to serum levels of gonadal and thyroidal hormones

Luc A. Comeau1,*, Steven E. Campana2, Ghislain A. Chouinard3, J. Mark Hanson3

1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
2Department of Fisheries and Oceans, Marine Fish Division, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
3Department of Fisheries and Oceans, Gulf Fisheries Centre, PO Box 5030, Moncton, New Brunswick E1C 9B6, Canada

ABSTRACT: Serum testosterone, estradiol-17β (E2), l-thyroxine (T4), 3,5,3¹-triiodo-l-thyronine (T3), and free (protein-unbound) T3 concentrations were examined in relation to the extensive (up to 650 km) seasonal migrations undertaken by southern Gulf of St. Lawrence cod Gadus morhua L.. Testosterone levels were low as the stock moved out of the Gulf of St. Lawrence in autumn, and increased only during the final stages of the return migration in spring. E2 in females peaked near the onset of the spring migration, and remained elevated until this migration was completed in early summer. However, we suggest that the changes in E2 levels are functionally tied with egg development and not with spring migratory behaviour. Free T3 showed no consistent pattern in relation to seasonal migrations, whereas T4 and T3 levels increased at the start of the autumn migration. We conclude that thyroid hormones may facilitate the onset of the autumn migration by enhancing metabolism, sensory physiology and swimming capacity.

KEY WORDS: Gadus morhua · Cod · Migration · Gonadal hormones · Thyroid hormones · Equinox · Gulf of St. Lawrence

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