Physiological and Biochemical Aspects of Ozone Toxicity to Rainbow Trout (Salmo gairdneri)

An acute toxicity curve for dissolved ozone (O 3 ) in soft water at 10 °C, using 10–13-cm rainbow trout (Salmo gairdneri) as the test species was calculated. The 96-h LC50 (95%, confidence interval) was 9.3 (8.1–10.6) μg/L. The lethal threshold level was about 8 μg/L mandating that a conservative margin of safety be used if ozone is employed as a fish disease control agent. Death apparently results from massive destruction of the gill lamellar epithelium together with a severe hydromineral imbalance. In partial chronic (3-mo) testing, 2 μg/L caused no significant biological damage while 5 μg/L caused some gill pathological changes and reduced feeding behavior. Accordingly, 2 μg/L is suggested as a provisional maximum safe exposure level, pending completion of life cycle studies. Thus, if ozone-treated water is discharged into the environment, dissolved O 3 should be reduced to at least the 2 μg/L level to minimize adverse impacts on salmonids in receiving waters. Key words: ozone, fish toxicity, acute ozone toxicity, chronic ozone toxicity, Salmo gairdneri