Epinephrine, norepinephrine, and cortisol concentrations in cannulated seawater‐acclimated rainbow trout (<i>Oncorhynchus mykiss</i>) following black‐box confinement and epinephrine injection

Abstract

The present study investigates the effect of cannulation and chronic‘black‐box’ confinement, as well as epinephrine administration (4–0 μg kg −1 ), on the degree and time‐course of alterations in trout ( Oncorhynchus mykiss ) catecholamine and cortisol concentrations. Plasma cortisol concentrations in seawater trout acclimated to 3–6° C reached 104 ng ml −1 1 day after cannulation/confinement and remained elevated above resting levels (8 ng ml −1 ) until 6 days post‐confinement. Although plasma epinephrine and norepinephrine generally declined over the period of confinement (day 1 approx. 12 nM; day 7 approx. 6 nM), norepinephrine titres were usually higher and more variable. Epinephrine injection caused elevations in plasma epinephrine levels but not in norepinephrine levels; epinephrine titres reaching 107 ± 26 nM (range 65–238 nM) at 2 min post‐injection and returning to pre‐injection levels by 30 min post‐injection. Plasma cortisol increased by 20 ng ml −1 following epinephrine administration. Based on the time‐course for post‐confinement alterations in plasma cortisol, it appears that up to a week may be required before cannulated fish are completely acclimated to ‘black‐box’ confinement. The findings suggest that meaningful results from experiments utilizing epinephrine injection and ‘black‐box confinement are contingent upon: (1) knowledge of circulating epinephrine levels shortly after injection (i.e. within 2 min post‐injection); and (2) an experimental design that takes into account the elevated cortisol titres that are inherent with cannulation/confinement and epinephrine injection.