Plasma prolactin and cortisol concentrations of stressed coho salmon, Oncorhynchus kisutch, in fresh water or salt water

Abstract

Juvenile 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.

The effects of confinement stress on circulating prolactin levels in rainbow trout ( Oncorhynchus mykiss ) in fresh water

“…Mean plasma PRL levels in unstressed fish during the present investigation lie within the range 2-5 ng ml-', similar to levels reported to occur in unstressed coho salmon, Oncorhynchus kisutch (Avella et al, 1991; -1-7 ng ml-'), sockeye, 0. nerku, and amago, 0. rhodurus, salmon (Yada et al, 1991; cl-4 ng ml-'), but lower than those previously reported in rainbow trout ; -10-30 ng ml-').…”

“…Complex die1 variation of plasma PRL is known to occur in mammals (Willoughby, 1980). Little is known of the variability of baseline PRL levels in fish, although previous studies on PRL dynamics in salmonid fish reveal there to be considerable variation with time in control fish (Prunet er al., 1985;Avella et al, 1991;Yada et al, 1991). Indeed, it might be argued that at least in Experiment 1, rather than reducing plasma PRL levels, the effect of stress is to oppose an elevation occurring in unstressed fish.…”

“…Spieler and Meier (1976) reported a significant reduction in circulating PRL levels in gold&h, Carassius auratus, subjected to capture and restraint, using a heterologous RIA (anti-pollack PRL, labeled ovine PRL) and, although partially validated for use with goldfish, the results must be interpreted with caution (Nicoll, 1975). Avella et al (1991), employing the same specific RIA as the present investigation, demonstrated that chronic stress (confinement for up to 5 days) elevated plasma PRL levels in juvenile coho salmon. Although it should be noted that in Avella's study fish at the presmolt and smolt stages were employed, these results are diametrically at variance with the observations made in the present study in which circulating levels of PRL were lower in stressed fish than in control fish.…”

“…Although widely studied in mammaIs (see, for example, Delitala et al, 1987) the effect of stress on PRL levels in fish has been examined in only two previous studies, with contradictory results. Spieler and Meier (1976) reported a stress-induced reduction in plasma PRL levels while, more recently, Avella et al (1991) observed an elevation of plasma PRL following stress. The present study was designed to clarify the effects of stress on PRL levels in fish by examining whether stress, in the form of confinement, with and without an accompanying deterioration in water quality, affects the circulating levels of PRL in freshwater-adapted rainbow trout, Oncorhynthus mykiss.…”

The effects of diet composition and ration on biotransformation enzymes and stress parameters in rainbow trout, Oncorhynchus mykiss

“…Ions out and in stressed freshwater fish brings ions in, thereby restoring the disrupted hydromineral balance caused by catecholamines (Avella et al, 1991).…”