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

Abstract

Serum testosterone, estradiol-17β (E 2 ), L-thyroxine (T 4 ), 3, 5, 3'-triiodo-L-thyronine (T 3 ), and free (protein-unbound) T 3 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. E 2 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 E 2 levels are functionally tied with egg development and not with spring migratory behaviour. Free T 3 showed no consistent pattern in relation to seasonal migrations, whereas T 4 and T 3 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.

Atlantic cod and snow crab predator–prey size relationship in the Gulf of St. Lawrence, Canada

“…1995 and references therein). Finally, large males moult from March to June in the NGSL (Sainte-Marie & Hazel 1992, Lovrich et al 1995 and from February to April in the SGSL (Hébert et al 2002), when most cod are outside the GSL (Hanson 1996, Ouellet et al 1997, Comeau et al 2001. A low incidence of large soft-shell male snow crabs in cod stomachs from the SGSL was confirmed by the analysis of 1887 additional cod stomachs collected from April to June of 2000 to 2003 (J. M. Hanson unpubl.…”

“…Only 20.5% of sets and 23.5% of stomachs were sampled in October or later in the NGSL. Similarly, 5.1% of sets and 10.7% of stomachs were sampled in or after October in the SGSL (Table A3 in the Appendix), when the migration of cod out of the area already is well underway (Hanson 1996, Comeau et al 2001). Therefore, it is possible that the scarcity of Instar I snow crab in cod stomachs simply reflected low availability to cod because of lack of temporal overlap.…”

“…1). Both stocks leave the GSL in late autumn and spend the winter months in the Laurentian Channel, south of Newfoundland and east of Nova Scotia (Chouinard & Fréchet 1994, Swain et al 1998, Castonguay et al 1999, Comeau et al 2001). Snow crab is abundant in both the NGSL and SGSL, sustaining important and lucrative fisheries.…”

Timing of Atlantic cod (Gadus morhua L.) seasonal migrations in the southern Gulf of St Lawrence: interannual variability and proximate control

“…Since gonadal recrudescence in southern Gulf cod begins in autumn (Schwalme and Chouinard, 1999;Comeau et al, 2001), an obvious advantage for leaving summer grounds as quickly as possible could be the enhancement of gonadal development in warm slope waters (see Hutchings and Myers, 1994). On the other hand, it does not appear that cod are capable of returning into the Gulf sooner the following spring, given the presence of ice (Fréchet, 1990) and cold waters described earlier.…”

Discovery of latitudinal gradient of triidothyronine concentrations in ectotherms as revealed from a cyprinid fish, the common roach Rutilus rutilus

“…These variations are associated with seasonal climate changes, thermal regime of water bodies, photoperiodism, breeding cycle (Cyr and Eales, 1996;Pavlidis et al, 2000;Eales, 2006), and migration (Baggerman, 1962;Comeau et al, 2001;Kitano et al, 2012). Although THs are involved in regulation of many physiological processes, serum TH concentrations positively correlate mainly with temperature during the annual cycle (Bau and Parent, 2000;Abbas et al, 2012;Bolotovskiy and Levin, 2015).…”