Behavioural studies of host, non-host and mate location by the Sea Louse, Caligus rogercresseyi Boxshall & Bravo, 2000 (Copepoda: Caligidae)

Sea lice are ectoparasites associated with wild and cultured salmonid species. In Chile, the dominant species affecting aquaculture is Caligus rogercresseyi (Boxshall & Bravo 2000), which is present in 99% of the established cultured cages, and is distributed on both salmonid and native hosts. The objective of this study was to test the hypothesis that the intra- and interspecific relationships of sea louse, C. rogercresseyi are mediated by semiochemicals, and to test the hypothesis that these chemical cues are responsible for differences in the susceptibility of the host. Our results show that an attractant effect was observed when conditioned water from Atlantic salmon, Salmo salar was used as the stimulus, indicating that adult males of C. rogercresseyi showed a preference for the host conditioned water. A repellent effect was elicited by conditioned water of the non-host, Hypsoblennius sordidus on adult males of C. rogercresseyi. Moreover, both young and adult females of C. rogercresseyi elicited an attractant response from conspecific adult males. A difference in the susceptibility of the host was observed when first generation (F1) of adult male C. rogercresseyi reared on Rainbow trout, Oncorhynchus mykiss were used in bioassays. F1 males were attracted to conditioned water of O. mykiss, but an avoidance behaviour was observed when they were stimulated by conditioned water of S. salar. In summary, our results provide evidence for the hypothesis that semiochemicals mediate the parasite-host interaction between C. rogercresseyi and S. salar similar to the relationship between Lepeophtheirus salmonis with conspecific females and host fish. Furthermore, these results support the hypothesis that semiochemicals could be involved in the difference in the susceptibility of the host.