Novel use of nanofiltered hyposaline water to control sea lice (Lepeophtheirus salmonis and Caligus elongatus) and amoebic gill disease, on a commercial Atlantic salmon (Salmo salar) farm

Abstract

Infestations by the salmon louse (Lepeophtheirus salmonis) and amoebic gill disease (AGD) are currently significant disease concerns facing the Atlantic salmon aquaculture industry in Ireland. Increasing seawater temperatures, and the move away from chemotherapeutants has prompted a new approach to researching areas of host-parasite life histories and using the physiology and behaviour of the parasites to develop novel control methods. Freshwater, with a low ionic concentration can be used to control sea lice and AGD but this may not always be available. Alternative treatments with hydrogen peroxide can prove toxic at the higher summer water temperatures experienced at this latitude. The aim of this study was to determine the efficacy of using nano-filtered hyposaline water as a non-medicinal method to reduce sea lice (L. salmonis and Caligus elongatus) infestation levels and amoebic gill disease under commercial conditions on an Atlantic salmon farm. To achieve this salmon were bathed in a tarpaulin filled with 5 ppt hyposaline water for 4.5 h and a regime of prophylactic bath treatments put in place to follow the production cycle. The nano-filtration unit consistently produced low saline water and resulted in a significant reduction of sea lice levels and AGD following routine 4.5 h baths. A 4.5 h bioassay of detached salmon lice confirmed both hyposaline and freshwater were equally effective against L. salmonis in the absence of the host.