Efficacy of fallowing in salmon farming to mitigate caligidosis: researching the environmental indicators

Fallowing in salmon farming is an effective tool in the management of the sea lice in the northern hemisphere (Bron et al. 1993; Ritchie 2004). The efficacy of this strategy is the result of coordinated work between the different companies present in the area, together with the application of this strategy during the effective time and area size. In Colaco Bay, near to Puerto Montt city, fallowing was implemented in the eight salmon farms present in the zone, within two months (May and June, 2007). Together with the help of several representatives from each company, we analysed this event, researching the potential indicators of sanity during three moments: before, during and after the fallowing time. Three biological units were used: 1) abundance of copepodids in the plankton, 2) infestation rate in the “guard salmon” (smolt of Salmo salar L.), introduced to each farm within 72 hours, and 3) parasites on native fish (specifically Eleginops maclovinus (Valenciennes 1830), “robalo”). All salmon farms selected in the area for this study were evaluated during four times. The results showed an exponential decrease of Caligus rogercresseyi (Boxshall & Bravo 2000) in the three components evaluated, obtaining the minimum values of intensity of C. rogercresseyi on smolts and juveniles of E. maclovinus within 51 postfallowing days (decreasing from 564 parasites/fish to 10 parasites/fish in smolts and from 10 parasites/fish to 2 parasites/fish in “robalo”). The copepodids in the plankton decreased by 70% in the same time period. Also, we detected the infestation of salmon smolts in the farms situated near to other areas with salmon farms in activity, specifically the Calbuco zone. Then, we conclude that all the biological indicators used in this study were effective for establishing the sanity of the Colaco Bay up to 42 post-fallowing days, and that the effectiveness of this measure is conditioned for the sanity of neighbouring zones, which is necessary to research the effective size of the area to obtain a good fallowing.