Host-specific in vitro colonisation of fish epithelia by gyrodactylids

Abstract

Background. The monogeneans, Gyrodactylus derjavini Mikailov, 1975 and G. salaris Malmberg, 1957, are specific parasites of brown trout, Salmo trutta L., and Atlantic salmon, S. salar L., respectively. Rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is also susceptible to G. derjavini but, similarly like brown trout, mounts a host response against this parasite. Rainbow trout can also experience infections with G. salaris but experiences generally lower infection levels compared to Atlantic salmon. This in vitro work was conducted in order to elucidate if the parasites could find and select specific host scales without influence of live and mobile hosts. Materials and methods. Using these two parasite species, a series of in vitro studies on host specificity were conducted. Scales with intact epithelia from rainbow trout, carp and salmon were cultivated and the two congeneric gyrodactylids (Gyrodactylus derjavini and G. salaris) were allowed to colonise the scales. Parasites attaching to the different scale types were monitored over 24 h. Results. The gyrodactylids colonised fish scales to a lesser extent, in vitro, compared to experiments where live fish were exposed to parasites. However, the parasites attached to a higher extent to in vitro-cultured fish scales with epithelia from their specific hosts: G. salaris relocated more often to salmon scales compared to the scales from rainbow trout and common carp, Cyprinus carpio L. In contrast, G. derjavini colonised preferentially cultured scales from rainbow trout and, to a lesser degree, scales from salmon. Conclusion. The work indicated that gyrodactylids colonising host epithelia are at least partly dependent on host movements but also have an ability to sense host-specific molecules due to their specific attachment to specific host scales.

Keywords

• Gyrodactylus derjavini
• G. salaris
• host specifi