Mitigating myxozoan disease impacts on wild fish populations

Abstract

We review evidence for population-level impacts of infections for four economically important myxosporean parasites: Myxobolus cerebralis, the cause of salmonid whirling disease (WD); Tetracapsuloides bryosalmonae, the cause of proliferative kidney disease (PKD) of salmonids, Ceratonova (syn. Ceratomyxa) shasta, the cause of enteronecrosis of salmonids and Myxobolus honghuensis, the cause of pharyngeal myxosporidiosis in gibel carp. WD is associated with a decline of rainbow and cutthroat trout populations in the intermountain region of the western USA and PKD with the decline of brown trout populations in Switzerland. Severe enteronecrosis in up to 62 % of outmigrating juvenile Chinook salmon combined with high mortality in sentinel fishes supports a potential adverse population-level impact of C. shasta infection. Similarly, declines in Crucian carp abundance in China have been associated with severe M. honghuensis infections. Accurate interpretation of impacts on wild populations is challenged by a general absence of long-term datasets providing information on population structure and abundance, disease prevalence and severity and on associated anthropogenic and natural factors that contribute to disease severity or host susceptibility. Efforts to mitigate adverse effects of these diseases in wild populations include the application of more sensitive methods to detect the parasites in fish, invertebrate hosts and water, use of risk assessments in fisheries management, use of temperature and silt or sediment control strategies within riparian habitats, and alternative stocking practices that take advantage of age-specific differences in host susceptibility or temperature regimes that are not conducive to disease development.