Authors

Discussion

The freshwater oomycete Saprolegnia parasitica is responsible for crippling damage to both the aquaculture industry and wild fish stocks. This fungal-like pathogen releases infective zoospores which germinate upon location of a fish host. The resulting mycelial hyphae colonise the host epidermal tissues before penetrating the muscle and blood layers. The chemotactic responses exhibited by S. parasitica zoospores greatly impact their ability to successfully locate a host. Chemotaxis is described as the movement of a cell/organism in response to an increasing or decreasing concentration gradient of a particular substance. It has been previously demonstrated that S. parasitica zoospores exhibit strong chemotactic activities towards amino acids. To date, no study has investigated whether S. parasitica zoospores exhibit varying chemotactic responses to the skin of different fish species. Such in vitro investigations represent a solid foundation for examining whether a host preference exists between S. parasitica isolates. The current study utilises both in vitro and in vivo methods to examine the zoospore chemotactic activities of four S. parasitica isolates. While crude in vitro methods do indicate that there are isolate-specific differences in zoospore chemotactic activity, these host preferences are not well demonstrated in lab-based challenge experiments.