Plasma prolactin and cortisol concentrations of stressed coho salmon Oncorhynchus kisutch in freshwater or saltwater

International audienceJuvenile coho salmon, Oncorhynchus kisutch, adapted to fresh water or seawater were either acutely handled or continuously stressed by severe confinement. Chronic stress, independent of external salinity, caused a gradual increase in the concentration of circulating prolactin that persisted for 1 to 5 days but lagged behind the cortisol response which peaked much more rapidly and remained elevated. Acutely stressed fish showed a rapid, more transient increase in plasma cortisol titer with no apparent effect on prolactin. Confinement appeared to be more stressful to fish in salt water than to those in fresh water, as judged by their sodium regulatory ability, hormone profiles, and mortality. Stress always elevated plasma prolactin concentrations, regardless of medium or developmental stage

Plasma prolactin and cortisol concentrations during salinity challenge of coho salmon (Oncorhynchus kisutch) at smolt and post-smolt stages

Circulating prolactin (PRL) and/or cortisol were measured in relation to hydromineral balance (internal osmotic pressure or plasma Na+ and K+ ) in smolt or post-smolt coho salmon (Oncorhynthus kisutch) to evaluate effects of salinity challenges. Freshwater (FW) challenge of seawater (SW)- adapted fish resulted in a peak of circulating PRL concentration 3 days after transfer, irrespective of the developmental stage or the date of transfer. Plasma PRL decreased thereafter, but remained higher at 14-l 5 days following FW entry than in the SW controls. Circulating cortisol levels were unchanged but a slight reduction of plasma Nat and osmolality occurred. Seawater challenge of FW-adapted fish elicited a rapid decline in circulating PRL concentrations to levels found in SW-acclimated fish; levels remained low thereafter. Plasma PRL showed a negative relationship with plasma cortisol and with internal osmotic pressures or natremia. Conversely, high circulating cortisol concentrations were associated with poor hypoosmoregulatory ability, probably reflecting a stress reaction