Control of Ichthyophthirius multifiliis using a combination of water filtration and sodium percarbonate: Dose-response studies

Morbidity and mortality caused by infections with the skin parasite Ichthyophthirius multifiliis Fouquet, 1876 is a major problem in freshwater fish farming in most climatic zones. In both traditional and re-circulated systems various chemicals have been applied to combat outbreaks with I. multifiliis. The present work provides a basis for establishing a preventive strategy against I. multifiliis in fish farms. Thus, water filtration can remove tomonts (and thereby prevent formation of tomocysts and theronts). When combined with the use of an environmentally neutral compound (sodium percarbonate, SPC) (releasing hydrogen peroxide) for eliminating infective theronts the infection can be kept at an acceptable level. SPC was tested and compared to formaldehyde (FA) — a traditionally used chemical against Ich at various concentrations (8, 16, 32 and 64 mg/l), temperatures (11–13 and 21–22 °C) and exposure times. SPC was found to have higher efficacy compared to FA but temperature and concentration of the chemical had significant influences on parasite survival. For both chemicals negative correlations were seen between survival of theronts and exposure time, temperature and concentration. A dose-response study conducted on tomonts showed that tomonts were exceedingly more tolerant towards both chemicals. Micro-filtration studies demonstrated that it was possible to filter out 100% of the tomonts using a mesh size of 80 µm. Therefore mechanical methods are recommended in order to eliminate tomonts whereby the subsequent production of tomocysts and theronts will be prevented.