Circulating catecholamine concentrations and effects on the cardiovascular system of the Chinook salmon (Oncorhynchus tshawytscha) on exposure to commercially used fish anaesthetics

Abstract

Whole animal, in situ and in vitro experiments were performed to investigate the dynamics of catecholamine release during anaesthesia and the consequent effects on the cardiovascular system of Chinook salmon. Blood pressure, heart rate, haematocrit, mean cell haemoglobin concentration (MCHC) and plasma catecholamine concentrations were used as indicators of cardiovascular function. In vivo experiments were performed to elucidate whether anaesthetic exposure per se stimulates catecholamine release. There was no correlation between changes in cardiovascular variables and plasma catecholamine concentrations during or after anaesthesia, suggesting that changes were due to anaesthetic induced hypoxia. When whole salmon blood was exposed to hypoxia, the pattern of Hct and MCHC changes were the same as those seen in vivo. However, deep anaesthesia elicited strong catecholamine release in both Chinook salmon and snapper. Despite plasma catecholamine levels above 500nML-¹ the circulating half-life in both species was <10 minutes. Changes in cardiovascular variables were consistent with typical adrenergic effects in teleost fish seen during hypoxia. These results suggest that anaesthetic induced hypoxia is the proximate stimulus for catecholamine release in anaesthetised salmon. However, in situ posterior cardinal vein (PCV) preparations did not secrete catecholamines when exposed to hypoxic saline, suggesting a higher control centre is responsible for hypoxic catecholamine release, in vivo. AQUI-S anaesthetic had no direct effect on catecholamine secretion patterns in field stimulated PCV preparations. However, in vitro myography experiments and in situ perfused tail preparations indicated that both AQUI-S and MS222 are potent vasodilators of peripheral vessels in salmon. Although anaesthesia per se does not stimulate catecholamine release in salmon, anaesthetic induced hypoxia does. Direct effects of anaesthetics on blood vessels may antagonise the actions of catecholamines released during hypoxia. This could have significant effects on cardiac return and gill perfusion patterns.