Henneguya zschokkei (Myxozoa) infection in cultured whitefish : Age-dependence, seasonality and distribution within host

Abstract

Whitefish (Coregonus lavaretus) is an important species for European fisheries and aquaculture.

Recently, the myxosporean Henneguya zschokkei has been observed to infect the muscles of whitefish in fish farms. Plasmodia of H. zschokkei prevent marketing of the fillet and cause economic losses. The factors associated with occurrence of the parasite in fish farms have not been investigated previously. We studied age-dependence, seasonality, and within-host distribution of H. zschokkei plasmodia in farmed whitefish by examining a total of 1599 fish. Distribution of plasmodia within the fish was not uniform. When the fillet was divided into parts, the number of plasmodia was positively correlated with the mass of the part, suggesting that larger muscles of whitefish may be particularly susceptible to, or preferred by H. zschokkei. Plasmodia were rarely found in 1 year old whitefish (prevalence 0.2%). The youngest age group substantially infected was 2 year old fish with the prevalence of 13.1%, which did not differ statistically from 3 year old fish with 17.1% infected. Mean intensity of infection in these three age groups was 1.0, 11.0 and 8.1 plasmodia per fish, respectively. The infections started to appear in August both in 1 and 2 year old fish, which suggests a seasonal hatching of parasite actinospores (the infective stage released from the definitive host). Condition of fish was not related to the number of plasmodia. Statement of relevance This is the first study of H. zschokkei in whitefish (C. lavaretus) in fish farm. There is a need for increased knowledge of H. zschokkei infection in cultured whitefish, as this species is being largely used in aquaculture and for stocking purposes.