Abstract

The marine copepodid Caligus rogercresseyi is the causative agent of Caligidosis, the most important parasitic disease for the Chilean salmon industry. Historically, C. rogercresseyi has been widely distributed in coastal waters of northern Patagonia (40 degrees 15'S to 49 degrees 16' S), where close to 90% of salmon farms are located. In 2017, sea lice were detected in farmed Atlantic salmon in the Magallanes region (south of 49 degrees 16' S), affecting salmon farms for the first time. This study aimed to identify the sea louse C. rogercresseyi infecting Atlantic salmon, and also to report measures and activities conducted by the Chilean Fisheries and Aquaculture Service (SERNAPESCA) in conjunction with the Caligidosis Reference Laboratory (University of Concepcion). The main actions were diagnosis and outbreak confirmation, case definition, surveillance, and implementation of control strategies. Here, the identification of C. rogercresseyi was confirmed through morphological and genetic analyses. In total, there were eight farms in the Magallanes region where at least one C. rogercresseyi individual was detected during 2017. Only in three case farms, C. rogercresseyi presented an epidemic behavior, reaching maximum levels of 24.5 adult lice/fish and 14 juvenile lice/fish. SERNAPESCA implemented different measures aimed to improve the sensitivity of the surveillance system, which yielded new case farms. The two farms with higher sea lice levels were treated with the organophosphate azamethiphos, resulting in a dramatic reduction of both adult and juvenile lice, although fish were re-infected a few weeks later. Further research is needed to determine the causes of this outbreak and evaluate its consequences for the local salmon industry.