Effects of capture and confinement on plasma cortisol concentrations in the snapper, Pagrus auratus

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Snapper (Pagrus auratus) were captured and their blood was sampled underwater by SCUBA divers. Cortisol concentrations in normally active fish ranged from 1.7 to 8.0 ng mL-1, with concentrations being highest in winter during the period when fish were sexually regressed. Underwater confinement in a net led to measurable increases in plasma cortisol (27 ng mL-1) by 60 min after capture. Fish captured by rod and line and confined in a 200-L tank on board the capture vessel showed a similar response latency. Further fish were captured by longlining or trawling and confined as before for periods of up to 1 h. Fish captured by a longline set for 1.5 h had initial mean plasma cortisol concentrations of 22 ng mL-1. These increased further over 60 min to a maximum of 58 ng mL-1. There was no difference in plasma cortisol between fish that were serially sampled or bled only once, indicating that increases in cortisol concentrations were due to capture stress and not the handling protocol. Plasma cortisol concentrations in fish taken by longlines set for up to 12 h remained high, showing that recovery from stress did not occur in fish left on the longline. Trawled fish showed similar increases in plasma cortisol, with concentrations reaching 42 ng mL-1 at 60 min after capture. Fish transferred to a 3000-L holding tank in the laboratory following capture by longline initially had high plasma cortisol concentrations (70 ng mL-1) . Concentrations remained high for at least 12 h but fell to 9 ng mL-1 after 48 h in the laboratory. The possible consequences of elevated cortisol concentrations for fish husbandry after capture and for post-mortem tissue quality are discussed.