Temperature-dependent infection with Ichthyophthirius multifiliis in rainbow trout

Ichthyophthiriosis is one of the most important parasitic diseases in aquaculture in Iran. The ciliate Ichthyophthirius multifiliis (ich) is a well described skin parasitic pathogen of large number of freshwater fishes. The parasite causes grate loss both in freshwater aquaculture enterprises worldwide as well as in natural ecosystems. In this study, the distribution of Ichthyophthirius multifiliis on surface of fish in 12°C and 20°C were investigated. Severity of the parasite was compared in 2 different temperatures, as well. Method & Materials: Heavily infected rainbow trout to ich were killed and escaping thomont were picked up and incubated for 48 hours in 12°C. Free swimming theronts intensified via centrifugation. Rainbow trout fingerlings were challenged with these theronts using immersion method (2000 theront per fish), then mortality and distribution of visible trophonts on fish body surface (skin, fins and gills) were counted 3, 6 and 9 days after challenge. Results & Conclusion: Results showed that not only the parasite was more severe in 20°C than 12°C but, pattern of throphonts distribution on fish surface was significantly different in two groups (P<0.05). Mortality after 10 days in 12°C and 20°C were 41% and 63%, respectively. Prevalence of ich in fins in 12C° was 37%, 44% and 39% in 3, 6 and 9 days after challenge, respectively, whereas it was 64%, 61% and 60% in 20°C. Prevalence of ich in skin in 12C° was 54%, 50% and 54% in 3, 6 and 9 days after challenge, respectively, versus it was 31%, 33% and 33% in 20°C. No significant difference was seen in prevalence of ich in gills in 20°C and 12°C . Results showed that prevalence of ich on the body surface depends on the water temperature in which infection occurred. Not only ich is more active in higher temperature, but the site of infection is another reason of higher mortality in 20C° than 12C°. Failure in osmoregulation is mentioned as an important reason of fish mortality in ichthyophthiriosis, hence in higher temperature more mortality occur because of skin penetration by ich but, in lower temperature infection shift to fins in which susceptibility is less.

کلیدواژه ها:

water temperature ، Ichthyophthirius multifiliis ، rainbow trout