Relation between salmon farming and the intensity of Caligus rogercresseyi on Eleginops maclovinus, during the fallowing of Colaco Bay, Chile

In Colaco Bay, near to Puerto Montt city (Chile), was implemented a fallowing in eight salmon farms by two months (May and June, 2007), as effect of the high intensity of sea lice. During this time, the sea lice of the native fishes (specifically Eleginops maclovinus, denominated “robalo”, postulated as a natural reservoir by Carvajal et al. (1998) were evaluated before of the fallowing, during this event and post-fallowing each fifteen days. Four farms were monitored; two off the Bay and two in the Bay. The results showed an exponential decrease of intensity and prevalence of Caligus rogercresseyi (Boxshall & Bravo, 2000) on this host, obtaining the minimum values to 51 post-fallowing days (2 parasites/fish, with 10% of prevalence). Other sea lice frequent on “robalo” is Lepeophtheirus mugiloidis (Villalba & Duran 1986), this specie was present with similar intensity (10 parasites/fish) and prevalence (60% - 100%) during all this study. Also, the rate Caligus/Lepeophtheirus presented the same decreasing detected for C. rogercresseyi, from 1.0 to 0.2. The post-fallowing situation was opposed, this rate increased to near 4.0. Then, we conclude that the presence of sea lice on “robalo” is directly related with the salmon farming in Colaco Bay, because this is one migratory and opportunistic species. Robalo is attracted by the availability of food, then this is infected by C. rogercresseyi, later they migrate to estuarine zones where remove this parasite. L. mugiloidis remain on this host probably by its mayor tolerance to the salinity changes. Our results were coincident with the situation observed in the north hemisphere, where the sympatric native salmons are impacted by salmon farms, collapsing the native salmon populations in the Pacific Ocean of Canada (Morton et al. 2004), and rainbow trout and Atlantic salmon in Europe (McVicar 2004). The