The ectoparasitic flagellate Ichthyobodo necator is known to induce ichthyobodosis in both wildand cultured host populations and notably young fish are vulnerable. The parasite infects gills, skin, and fins and causes severe epizootics in aquaria, hatcheries, and rearing ponds worldwide (Urawa and Kusakari 1990, Urawa 1992, Urawa 1993). Rainbow trout (Oncorhynchus mykiss) farming in Denmark is currently suffering from I. necator infections and trout farmers apply formaldehyde bath treatments for control. A series of antiparasitic compounds were tested by Tojo et al. (1994) and Tojo and Santamarina (1998) elucidating efficacies of 11 drugs used for bath treatment and further 32 drugs administered orally against I. necator infection of rainbow trout. It was shown that oral treatments using metronidazole (40 g · kg–1 feed, 10 days), secnidazole (20 g · kg–1 feed, 2 days), and triclabendazole (40 g · kg–1 feed, 5 days) were effective and did show elimination of the flagellates. The first two nitroimidazoles are banned for use in fish production within the EU. In addition, although oral medical treatments may have a potential role in future control it is worth investigating auxiliary water bath treatments based on environmentallyfriendly compounds. Recently Farmer et al. (2013) tested copper sulphate, potassium permanganate, and peracetic acid against I. necator infection of channel catfish but the only substance which significantly reduced the parasite burden and improved the survival of I. necator-infected channel catfish was copper sulphate applied at a rate of 2.1 mg · L–1 (once daily at 24-h intervals for 3 days). ACTA ICHTHYOLOGICA ET PISCATORIA (2013) 43 (2): 139–143 DOI: 10.3750/AIP2013.43.2.06