Effectiveness of Freshwater on Caligus rogercresseyi Juveniles.

Freshwater is a non-pharmaceutical tool used for the control of Caligus infestation with a proven effect on adult and larval stages. However, the minimum exposure time to achieve a greater effect (100%) on juvenile stages has not been determined through in vivo tests. Therefore, it is important to determine these minimum times on C. rogercresseyi chalimus, considering that freshwater baths should be performed with a wellboat to achieve the greatest effect. A study was thus formulated that allowed us to evaluate the effect of applying freshwater treatment on C. rogercresseyi juveniles at different exposure times through in vivo tests on Atlantic salmon (Salmo salar). The results indicated that a treatment of more than 2.5 h with freshwater induces a greater effect (100%) and mortality (~95%) on juvenile stages, at least at chalimus III-IV. Juvenile stages are a critical point in population dynamics and control of the parasite, since those that survive treatment increase the possibility of augments in parasitic loads in the short term, and cause loss of sensitivity. Based on these results, freshwater treatment exposure time should exceed 2.5 h in order to ensure effectiveness on parasite stages and, therefore, to avoid development of resistance to freshwater and prolong the useful life of this non-pharmaceutical tool.