The impact of the water moulds Saprolegnia diclina and Saprolegnia parasitica on natural ecosystems and the aquaculture industry

•Saprolegnia diclina is an oomycete that infects eggs of aquatic animals.•Saprolegniosis is a serious problem in aquaculture and natural ecosystems.•Very few measures to control Saprolegniosis are available.

A very large number of diseases in agriculture and aquaculture are caused by fungal-like micro-organisms, classified as Oomycetes or water moulds. Collectively, oomycetes represent a huge threat to global food security. In addition, several oomycetes can cause environmental disasters, by wiping out native species of trees, crustacians and amphibians. The group representing the aquatic oomycetes are relatively understudied in contrast to their terrestrial counterparts that predominantly infect plants (e.g. Phytophthora, Pythium and Bremia spp.). This review focuses on the unique characteristics of two aquatic Oomycetes, Saprolegnia parasitica and Saprolegnia diclina with respect to their impact on aquaculture, animal health and the surrounding environment. The species characteristics, ecology, biology, infectivity and identification methods are described and the latest research insights are discussed.