Some physiological aspects of five fish anaesthetics in rainbow trout were investigated. The effects of benzocaine, 2-phenoxyethanol, MS-222 (Sandoz), metomidate, and carbon dioxide gas (CO2) on acid–base regulation, hematocrit, blood gases, and cortisol and adrenaline concentrations were determined in resting rainbow trout fitted with chronic catheters in the dorsal aorta. A severe hypoxia developed with the cessation of breathing in deep anaesthesia. This was accompanied by a rise in blood [Formula: see text] and adrenaline concentration, and a fall in blood pH. Blood bicarbonate concentrations remained unchanged and cortisol concentrations declined with time. There was a transient increase in hematocrit coinciding with the increase in adrenaline concentrations.

The effect of Chattonella exposure on the acid-base status of the yellowtail Seriola quinqueradiata was analyzed to assess the validity of the hypothesized mechanism of fish kill by this plankton species. Based on the finding that gill carbonic anhydrase was inactivated in fish exposed to Chattonella, it was hypothesized that this inactivation resulted in certain physiological disorders such as decreases in blood pH and Po2. None of the acid-base variables measured in this study (arterial blood pH (pHe), red blood cell intracellular pH (pHi), Pco2 (Paco2), and total CO2 of plasma (Taco2p)) varied substantially from their control values after the onset of exposure except for some increases in pHi. It was only the terminal blood samples that demonstrated sharp decreases in pHe and pHi and elevation of Paco2. In contrast, arterial Po2 decreased rapidly after the onset of plankton exposure. Overall these results do not support the above hypothesis.