title: Growth hormone and cortisol treatment stimulate seawater tolerance in both anadromous and landlocked Arctic charr.
abstract: In a comparative experiment the effect of cortisol and growth hormone (GH) on the hypo-osmoregulatory ability of a landlocked and an anadromous strain of Arctic charr (Salvelinus alpinus) was investigated. Cortisol and GH were implanted either alone or in combination, and the fish were exposed to a 24 h seawater challenge test (SWT) on days 14 and 28 after implantation. Hypo-osmoregulatory ability, measured as plasma osmolality and chloride concentration after the SWTs, was better in the anadromous than in the landlocked strain, irrespective of treatment. However, cortisol provided a strong stimulation of hypo-osmoregualtory ability in both strains, and this stimulation seemed to be potentiated by GH in an additive manner. Improved hypo-osmoregulatory ability in GH+cortisol treated anadromous Arctic charr was accompanied by increased gill Na(+), K(+)-ATPase activity and Na(+)-K(+)-2Cl(-) cotransporter protein abundance, but no changes in gill Na(+),K(+)-ATPase alpha1a and alpha1b mRNA levels. For landlocked charr the improved hypo-osmoregulatory ability in GH+cortisol treated fish was accompanied only with an increase in gill Na(+)-K(+)-2Cl(-) cotransporter protein abundance. Hormone treatment caused an improvement of hypo-osmoregulatory ability that was of approximately the same magnitude in the landlocked as in the anadromous Arctic charr. This suggests that the lack of spontaneous development of hypo-osmoregulatory ability often seen in landlocked populations of Arctic charr may depend, at least partly, on a lack of the hormonal activation seen in anadromous populations.
authors.affiliation: Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ojima
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Pettersen
authors.forename: Judith
authors.initials: J
authors.lastname: Wolkers
authors.forename: Helge K
authors.initials: HK
authors.lastname: Johnsen
authors.forename: Even H
authors.initials: EH
authors.lastname: Jørgensen