title: Photoperiod effects on plasma cortisol levels in Gasterosteus aculeatus.
abstract: No diel variations of plasma cortisol levels were found in Gasterosteus aculeatus acclimated to two different photoperiod conditions: 14L:10D and 9L:15D. However, under long photoperiods, G. aculeatus exhibited higher plasma cortisol levels than under short photoperiods, suggesting that elevated plasma cortisol levels are associated with the spring migration and/or reproductive activities. This decrease of plasma cortisol levels is particularly marked in male G. aculeatus. Under the 9L:15D photoperiod, males had lower plasma cortisol levels than females, in contrast to 14L:10D, where no significant sex differences were found.
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D005399:Fishes / Q000097:blood*; D006854:Hydrocortisone / Q000097:blood* / Q000502:physiology; D008027:Light; D008297:Male; D012621:Seasons; D012737:Sex Factors; D013997:Time Factors
chemical_list: D006854:Hydrocortisone