Sublethal effects of treated liquid effluent from a petroleum refinery. IV. Respiratory movements and coughing of rainbow trout

Rainbow trout increased the frequency of gill irrigation in linear relation to the concentration of treated refinery effluent. Full-strength effluent resulted in a significantly higher frequency than in clean water, but 50% and lower did not, because of variation in response. Coughing rate increased sharply and was a less variable measure of response. A concentration of 50% effluent caused significantly more coughs than in clean water, while 25% did not. The eight samples of effluent caused little lethality at full strength, and average physico-chemical characteristics were near or below Canadian regulatory limits, except for elevated oil and grease. Coughing rate shows promise as a rapid initial method for sublethal screening or monitoring of refinery effluents.