Saprolegnia - Characteristics of Infection

Characteristics of Infection

Saprolegnia is generally a secondary pathogen, though in the right circumstances, it can act as primary. It most frequently targets fish, both in the wild and in tank environments. Through cellular necrosis and other epidermal damage, Saprolegnia will spread across the surface of its host as a cotton-like film. Though it often stays in the epidermal layers, the mould does not appear to be tissue specific. A Saprolegnia infection is usually fatal, eventually causing haemodilution, though the time to death varies depending on the initial site of the infection, rate of growth and the ability of the organism to withstand the stress of the infection.

The extensive mortalities of salmon and migratory trout in the rivers of western Europe in the 1970s and 1980s in the UDN outbreak were probably almost all ultimately caused by the secondary Saprolegnia infections.

Historial evidence suggest the Saprolegnia species affecting Australian freshwater fish may be an introduced strain, imported in the 1800s with exotic fish species.