Fish in hot water: Hypoxaemia does not trigger catecholamine mobilization during heat shock in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) exposed to an acute heat shock (1 h at 25 °C after raising water temperature from 13 °C to 25 °C over 4 h) mount a significant catecholamine response. The present study investigated the proximate mechanisms underlying catecholamine mobilization. Trout exposed to heat shock in vivo exhibited a significant reduction in arterial O2 tension, but arterial O2 concentration was not affected by heat shock, nor was catecholamine release during heat shock prevented by prior and concomitant exposure to hyperoxia (to prevent the fall in arterial O2 tension). Thus, catecholamine mobilization probably was not triggered by impaired blood O2 transport. Heat-shocked trout also exhibited an elevation of arterial CO2 tension coupled with a fall in arterial pH, but these factors are not expected to trigger catecholamine release. The changes in blood O2 and CO2 tension occurred despite a significant hyperventilatory response to heat shock. Future studies should investigate whether catecholamine mobilization during heat shock in rainbow trout is triggered by a specific effect of high temperature activating the sympathetic nervous system via a thermosensitive transient receptor potential channel.