Resistance of ozone of zoospores of the thraustochytrid abalone parasite, Labyrinthuloides haliotidis (protozoa: Labyrinthomorpha)

Ozone proved ineffective in eliminating the abalone parasite Labyrinthuloides haliotidis from the water supply of an abalone hatchery. Zoospores of the abalone parasite survived exposure to 0.30 mg ozone/l of sea water for 19 min with no apparent detrimental effects. Also, zoospores survived exposure to the highest ozone concentration tested (0.97 mg ozone/l for 25 min) but the treatment appeared to kill or injure some of them judging from the marked delay before growth was observed following transfer to nutrient medium. Zoospores of L. haliotidis also survived longterm (at least 7 days) exposure to low levels of ozone (0.025–0.070 mg ozone/l) in sea water.