Distribution, prevalence, and pathology of a microsporidian infecting freshwater sculpins.

Microsporidian infections are common in many fish species, yet detailed studies of these parasites in ecologically important wild populations are rare. Phylogenetic analysis using rDNA sequence data and parasite morphology indicate that mottled sculpin Cottus bairdii and slimy sculpin C. cognatus are hosts for Glugea sp.

Virulence is context-dependent in a vertically transmitted aquatic host-microparasite system.

Recent work has suggested that the outcomes of host-symbiont interactions can shift between positive, neutral and negative depending on both biotic and abiotic conditions. Even organisms traditionally defined as parasites can have positive effects on hosts under some conditions. For a given host-parasite system, the effects of infection on host fitness can depend on host vigour, route of transmission and environmental conditions.