title: Lack of hormonal stimulation prevents the landlocked Biwa salmon (Oncorhynchus masou subspecies) from adapting to seawater.
abstract: Landlocking of salmon relaxes selective pressures on hypoosmoregulatory ability (seawater adaptability) and may lead to the abandonment of its physiological system. However, little is known about the mechanism and consequence of the process. Biwa salmon is a strain/subspecies of Oncorhynchus masou that has been landlocked in Lake Biwa for an exceptionally long period (about 500,000 years) and has low ability to adapt to seawater. We compared activity of gill Na(+),K(+)-ATPase (NKA) of Biwa salmon with those of anadromous strains of the same species (masu and amago salmon) during downstream migration periods and after exogenous hormone treatment. Gill NKA activity in anadromous strains increased during their migration periods, while that in Biwa salmon remained low. However, treatments of Biwa salmon with growth hormone (GH) and cortisol increased gill NKA activity. Cortisol treatment also improved the whole body seawater adaptability of Biwa salmon. Receptors for GH and cortisol responded to hormonal treatments, whereas their mRNA levels during downstream migration period were essentially unchanged in Biwa salmon. Circulating levels of cortisol in masu salmon showed a peak during downstream migration period, while no such increase was seen in Biwa salmon. The present results indicate that Biwa salmon can improve its seawater adaptability by exogenous hormonal treatment, and hormone receptors are capable of responding to the signals. However, secretion of the endogenous hormone (cortisol) was not activated during the downstream migration period, which explains, at least in part, their low ability to adapt to seawater.
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan;
authors.forename: Takuro
authors.initials: T
authors.lastname: Nakajima
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan;
authors.forename: Haruka
authors.initials: H
authors.lastname: Shimura
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan;
authors.forename: Miyuki
authors.initials: M
authors.lastname: Yamazaki
authors.affiliation: Shiga Prefecture Fishery Experiment Station, Shiga, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Fujioka
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan;
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ura
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan;
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hara
authors.affiliation: Faculty of Fisheries Sciences, Hokkaido University, Hokkaido, Japan; mune@fish.hokudai.ac.jp.
authors.forename: Munetaka
authors.initials: M
authors.lastname: Shimizu
mesh_terms: D025041:Animal Migration; D000818:Animals; D029941:Fish Proteins / Q000378:metabolism; D005618:Fresh Water; D005786:Gene Expression Regulation; D005880:Gills / Q000201:enzymology; D013006:Growth Hormone / Q000097:blood / Q000494:pharmacology*; D006854:Hydrocortisone / Q000097:blood / Q000494:pharmacology*; D017683:Oncorhynchus / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D054712:Salinity; D055049:Salt Tolerance / Q000187:drug effects*; D012621:Seasons; D012623:Seawater; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013045:Species Specificity; D013997:Time Factors
chemical_list: D029941:Fish Proteins; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D011986:Receptors, Somatotropin; C029360:hydrocortisone receptor; D013006:Growth Hormone; D000254:Sodium-Potassium-Exchanging ATPase; D006854:Hydrocortisone
keywords: Na+-K+-ATPase; hormone; landlocked salmon; relaxation of selection pressure; seawater adaptability