Detection of Tenacibaculum spp. in Caligus rogercresseyi: Evidence of Potential Pathogen Carriage in Salmon Aquaculture

Sea lice (Caligus rogercresseyi) are major ectoparasites in Chilean salmon aquaculture, causing economic losses and increasing fish susceptibility to secondary infections. Tenacibaculosis has recently emerged as the second leading cause of mortality in farmed salmon. Understanding whether sea lice may harbor or transmit bacterial pathogens is therefore highly relevant. A sea lice survey was conducted at an Atlantic salmon (Salmo salar) farm in the Los Lagos Region, Chile. Twenty adult parasites (10 ovigerous females and 10 males) were analyzed using an integrated approach combining immunohistochemistry (IHC) with specific antibodies and conventional PCR with appropriate controls. IHC revealed positive signals for Tenacibaculum maritimum in the gastrointestinal tract and cuticle, and for Tenacibacuum dicentrarchi in the cuticle and ovigerous sac of C. rogercresseyi. A specific PCR test confirmed the presence of both pathogens, yielding amplification products of 1088 bp for T. maritimum and 284 bp for T. dicentrarchi. This study provides the first dual evidence, by PCR and IHC, of Tenacibaculum species in C. rogercresseyi. These findings suggest that sea lice may play a role in pathogen dynamics in salmon farming, highlighting the need for further research on their contribution to disease transmission within aquaculture systems.