A Review: Factors Affecting Outbreaks of Saprolegniosis on Aquatic Animals

Abstract

In this paper, we review the current knowledge regarding factors affecting the outbreaks of saprolegniosis. Saprolegniosis is a serious disease which can cause significant economic losses in aquaculture. Oomycetes are considered to be responsible for the disease. Outbreaks of saprolegniosis occur when equilibrium between pathogenic oomycetes and host resistance is disturbed. This may be the result of an increase in numbers or virulence of the zoospores of oomycetes in the water, or an increase in the susceptibility of the host. The presence of oomycetes zoospores in the environment is regarded as one of the most important causes of saprolegniosis. However, important differences have been found between plant and animal pathogenic oomycetes and appear to be related not only to tactic responses to environment, but also to infection strategies to a host. In addition, fish are more susceptible to infection by pathogenic oomycetes when physically injured, stressed or infected. Furthermore, water environmental factors, such as temperature, salinity, and microorganisms, should be carefully considered since they play a key role in the outbreaks of saprolegniosis.