Considering elements of natural strategies to control salmon lice infestation in marine cage culture

Abstract

Salmon lice are a severe problem in salmonid aquaculture and also affect wild salmon smolts migrating through fjord systems in spring. To keep the lice burden within acceptable limits, frequent use of chemical delousing has resulted in the parasite becoming resistant to these treatments. Alternative thermal and mechanical delousing practices induce welfare problems and loss of farmed fish. To avoid losing the constant arms race with the parasite, we need a new approach to the problem. Inspired by the natural host-parasite balance, we propose a change in salmonid aquaculture practices by combining and improving existing management strategies for a more holistic and sustainable vision of the industry. Before salmonids were farmed in open cages, few hosts were available for salmon lice during winter, which reduced the salmon lice populations to a minimum when the wild smolts were migrating to sea. Thus, the natural strategy is to decrease host availability for a sufficient period of time to allow salmon lice nauplii to die of starvation. Due to the long survival and drift of the nauplii, it is important to significantly increase the distance between open farming units, either by organising and aggregating farms in extensive fallowing areas with significant distance to other corresponding areas or by controlling water flow through active production units during extensive fallowing. Here we primarily address environmental interactions. Economic and juridical implications of the proposed strategy are not discussed in detail. However, we do briefly suggest relevant current regulations and possible costs and benefits of reducing delousing treatment intensity.

Molecular quantification of parasitic sea louse larvae depends on species and life stage

“…Two prominent species in the North Atlantic, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus (von Nordmann), are well‐known for their impacts on mariculture species and wild fish populations. In particular, L. salmonis currently represents the greatest challenge to the Norwegian salmon farming industry due to financial impact, environmental sustainability and fish welfare (Dempster et al., 2021; Karlsen et al., 2023; Stene et al., 2022; Taranger et al., 2015). L. salmonis is a native ectoparasite of wild Atlantic salmon ( Salmo salar , L.), sea trout ( Salmo trutta , L.) and Arctic charr ( Salvelinus alpinus , L.) but has increased in population size due to the increased scale of Atlantic salmon and rainbow trout ( Oncorhynchus mykiss , Walbaum) aquaculture operations in Norway over the last 60 years (Finstad et al., 2021; Heuch et al., 2005).…”