Resmoltification in wild, anadromous Arctic char (Salvelinus alpinus): a survey of osmoregulatory, metabolic, and endocrine changes preceding annual seawater migration

Abstract

Anadromous Arctic char (Salvelinus alpinus) migrate to seawater every summer for feeding and spend the rest of the year overwintering in fresh water. We investigated whether annual seawater migration is preceded by changes in hyposmoregulatory capacity, intermediary metabolism, and the plasma levels of hormones known to play a role in salmonid seawater preadaptation (smoltification). Wild, anadromous Arctic char were sampled in their overwintering lake in April and May and during the period of downstream migration in June. Our results demonstrate a fourfold seasonal increase in gill Na+/K+ ATPase activity, with maximum levels in descending migrants that also displayed prime hyposmoregulatory capacity. Hepatosomatic index and activities of key liver enzymes also increased during spring, indicating a general increase in liver metabolic capacity. These changes were accompanied by increased plasma cortisol and thyroxine levels, decreased plasma growth hormone levels, and unchanged plasma levels of insulin-like growth factor-I and 3,5,3′-triiodothyronine. Our results indicate that wild, anadromous Arctic char resmoltify every spring, and this involves a shift from an energy-conserving overwintering state to a state where they become osmotically and metabolically prepared for their annual feeding migration to seawater.

Genomic tools for new insights to variation, adaptation, and evolution in the salmonid fishes: a perspective for charr

“…The switch to anadromy seems to be partly genetic and partly triggered by environmental conditions and smoltification involves a suite of changes including osmo-regulatory changes to survive in salt water, revised foraging behaviour, and developmental rate (Aas-Hansen et al, 2005;Jonsson & Jonsson, 2009;Dodson et al, 2013). This process is fundamentally similar across species in Oncorhynchus, Salmo and Salvelinus (Dodson et al, 2013).…”

“…It is also very important from a conservation perspective because it involves how organisms interact and can manage their changing environments including dams, habitat degradation, and pollution (Aas-Hansen et al, 2005;Jonsson & Jonsson, 2009;Dodson et al, 2013). Therefore, probably the most intensive area of ecological genomics research on salmonids to date has focused on the genetic basis of this trait.…”

Long-term fasting in the anadromous Arctic charr is associated with down-regulation of metabolic enzyme activity and up-regulation of leptin A1 and SOCS expression in the liver.

“…In captive offspring of anadromous charr, feeding commences in May (Tveiten et al, 1996;Bottengård and Jørgensen, 2008;Aarseth et al, 2010). In wild anadromous charr, appetite seems to return in early May (Aas-Hansen et al, 2005), whereas seaward migration takes place 3 to 4weeks later (AasHansen et al, 2005;Jensen et al, 2012). During the pre-migratory period the fish apparently find little food, and their condition factor continues to decrease until the time of downstream migration, when it may be as low as 0.70 (Nilssen et al, 1997;Aas-Hansen et al, 2005).…”

“…In wild anadromous charr, appetite seems to return in early May (Aas-Hansen et al, 2005), whereas seaward migration takes place 3 to 4weeks later (AasHansen et al, 2005;Jensen et al, 2012). During the pre-migratory period the fish apparently find little food, and their condition factor continues to decrease until the time of downstream migration, when it may be as low as 0.70 (Nilssen et al, 1997;Aas-Hansen et al, 2005). Hence, the anadromous life strategy of Arctic charr incorporates a prolonged, voluntary anorexia with emaciation, indicating high tolerance to food deprivation.…”

Examination of liver and muscle glycogen and blood glucose levels of Capoeta umbla (Heckel, 1843) living in Hazar Lake and Keban Dam Lake (Elazig, Turkey)

“…Aas-Hansen et al (2005) stated that the condition factor (and relevantly liver glycogen values) of Salvelinus alpinus which is an anadro-mous fish rapidly decreased during their migration from fresh water to sea. In most of the seasonal studies (like this one), fish were obtained by hunting, so many resear-chers stated that abnormal changes may occur on the level of muscle glycogen levels.…”