|Straus, David - Dave|
Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/24/2009
Publication Date: 9/7/2009
Citation: Meinelt, T., Matzke, S., Stuber, A., Pietrock, M., Wienke, A., Mitchell, A.J., Straus, D.L. 2009. Toxicity of peracetic acid (PAA) to tomonts of Ichthyophthirius multifiliis. Diseases of Aquatic Organisms. 86(1):51-56. Interpretive Summary: Ich is a common parasite found throughout the world and attaches to the skin or gills of most fish. These parasites appear as small white spots the size of a pin head or smaller. They can be devastating to aquaculture and can be passed to nearby facilities through poor management practices. While Ich is on the fish, it is protected by the fish mucus. This study looked at the acute toxicity of a new compound, peracetic acid (PAA), to different life stages of this parasite after they had been removed from the skin of fish. We found that PAA was toxic to Ich for several hours after being removed from the skin, but when the parasite had settled to the bottom and started to for a jelly-like coat, they became much less susceptible to chemical treatment.
Technical Abstract: The free-living infective theront of Ichthyophthirius multifiliis historically has been thought to be the only stage susceptible to treatment. A technique is introduced to determine the toxicity of compounds to the detached trophont, the settled tomont and the developing tomites within the tomont that emerge as theronts. The toxicity of Wofasteril(c) E400 (40% peracetic acid, PAA) to free-living forms of I. multifiliis was determined shortly after trophonts were physically removed from the surface of the fish and at 2.5 and 24 h after removal. Results indicate that 0.6 mg/L - 0.9 mg/L PAA killed 39 to 82% of the newly released trophonts within 48 h when treated immediately. In a second experiment, trophonts were allowed to settle for 2.5 h after sampling from the skin and then treated for 12 h; concentrations =0.5 mg/L PAA produced significantly less theronts than the controls. In a third experiment, tomonts that were exposed to PAA 24 h after sampling from the skin and treated for 2 or 4 h produced a variable amount of theronts, but the concentrations tested (0.5 – 3.0 mg/L) did not halt theront production. This research demonstrates that encysted I. multifiliis are less susceptible to chemical treatments.