DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03198

Presence of selected pathogens on the gills of five wrasse species in western Norway

A. Steigen*, A. Nylund, H. Plarre, K. Watanabe, E. Karlsbakk, Ø. Brevik

*Email: andreas.steigen@bio.uib.no

ABSTRACT: The objective of this study was to identify gill pathogens in Labridae (wrasse) species used as cleaner fish to control salmon louse in Western Norwegian aquaculture. Wrasse are often moved over long distances raising issues of fish health, welfare and pathogen transmission. Histological examination and real time RT PCR analysis of the gills from Centrolabrus exoletus, Ctenolabrus rupestris, Labrus bergylta, Labrus mixtus, and Symphodus melops revealed several pathogens: a new species of Ichthyobodo, Paramoeba perurans, microsporidia, trichodinids, Hatschekia spp., Candidatus Similichlamydia labri and two putative new species of chlamydia. Cand. S. labri or closely related chlamydia were present on most wrasse specimens. Epitheliocysts on the gills of L. mixtus contained large inclusions (120 µm) with actiniae radiating from the inclusion membrane. A possible member of the Candidatus family Parilichlamydiaceae was present at a high prevalence on the gills of L. mixtus, L. bergylta and C. rupestris. Sequencing the 16S rRNA gene showed 93.9% similarity to Candidatus S. labri and 96.8% similarity to Cand. Parilichlamydia carangidicola from the gills of Seriola lalandi. This chlamydia probably represents a new species within the order Chlamydiales, family Cand. Parilichlamydiaceae. The other chlamydia detected on gills of S. melops could represent a new species in Cand. genus Syngnamydia. Ichthyobodo sp. and Paranucleospora theridion were detected on the gills of nearly all individuals, while Paramoeba spp. were detected on the gill of L. bergylta and L. mixtus. Trichodinids, microsporidia, and parasitic copepods had low prevalence. Viral haemorrhagic septicaemia (VHS) virus was not detected.