title: Temporal changes in blood variables during final maturation and senescence in male sockeye salmon Oncorhynchus nerka: reduced osmoregulatory ability can predict mortality.
abstract: This study is the first to characterize temporal changes in blood chemistry of individuals from one population of male sockeye salmon Oncorhynchus nerka during the final 6 weeks of sexual maturation and senescence in the freshwater stage of their spawning migration. Fish that died before the start of their historic mean spawning period (c. 5 November) were characterized by a 20-40% decrease in plasma osmolality, chloride and sodium, probably representing a complete loss of osmoregulatory ability. As fish became moribund, they were further characterized by elevated levels of plasma cortisol, lactate and potassium. Regressions between time to death and plasma chloride (8 October: P < 0·001; 15 October: P < 0·001) indicate that plasma chloride was a strong predictor of longevity in O. nerka. That major plasma ion levels started to decline 2-10 days (mean of 6 days) before fish became moribund, and before other stress, metabolic or reproductive hormone variables started to change, suggests that a dysfunctional osmoregulatory system may initiate rapid senescence and influence other physiological changes (i.e. elevated stress and collapsed reproductive hormones) which occur as O. nerka die on spawning grounds.
authors.affiliation: Centre for Applied Conservation Research and Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada. kenmjeffries@gmail.com
authors.forename: K M
authors.initials: KM
authors.lastname: Jeffries
authors.forename: S G
authors.initials: SG
authors.lastname: Hinch
authors.forename: M R
authors.initials: MR
authors.lastname: Donaldson
authors.forename: M K
authors.initials: MK
authors.lastname: Gale
authors.forename: J M
authors.initials: JM
authors.lastname: Burt
authors.forename: L A
authors.initials: LA
authors.lastname: Thompson
authors.forename: A P
authors.initials: AP
authors.lastname: Farrell
authors.forename: D A
authors.initials: DA
authors.lastname: Patterson
authors.forename: K M
authors.initials: KM
authors.lastname: Miller
mesh_terms: D000375:Aging / Q000097:blood*; D000818:Animals; D004958:Estradiol / Q000097:blood; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D012474:Salmon / Q000097:blood / Q000254:growth & development*; D012741:Sexual Maturation; D013312:Stress, Physiological; D013739:Testosterone / Q000097:blood; D013997:Time Factors; D014882:Water-Electrolyte Balance
chemical_list: D013739:Testosterone; D004958:Estradiol; D006854:Hydrocortisone