Prevention not cure: a review of methods to avoid sea lice infestations in salmon aquaculture

Abstract

The Atlantic salmon aquaculture industry still struggles with ectoparasitic sea lice despite decades of research and development invested into louse removal methods. In contrast, methods to prevent infestations before they occur have received relatively little research effort, yet may offer key benefits over treatment‐focused methods. Here, we summarise the range of potential and existing preventative methods, conduct a meta‐analysis of studies trialling the efficacy of existing preventative methods and discuss the rationale for a shift to the prevention‐focused louse management paradigm. Barrier technologies that minimise host–parasite encounter rates provide the greatest protection against lice, with a weighted median 76% reduction in infestation density in cages with plankton mesh ‘snorkels’ or ‘skirts’, and up to a 100% reduction for fully enclosed cages. Other methods such as geographic spatiotemporal management, manipulation of swimming depth, functional feeds, repellents and host cue masking can drive smaller reductions that may be additive when used in combination with barrier technologies. Finally, ongoing development of louse‐resistant salmon lineages may lead to long‐term improvements if genetic gain is maintained, while the development of an effective vaccine remains a key target. Preventative methods emphasise host resistance traits while simultaneously reducing host–parasite encounters. Effective implementation has the potential to dramatically reduce the need for delousing and thus improve fish welfare, productivity and sustainability in louse‐prone salmon farming regions.

Effect of handling and crowding on the susceptibility of Atlantic salmon (Salmo salar L.) to Lepeophtheirus salmonis (Krøyer) copepodids

“…Additionally, there is increasing interest in prevention methods (Barrett et al., 2020). Snorkel sea cages are currently presented as an interesting approach to diminish sea lice loads on farmed salmon, with no effect on fish growth and a welfare index based on fish visual appearance (Geitung et al., 2019; Oppedal et al., 2017; Stien et al., 2016).…”

Towards cost‐effective biofouling management in salmon aquaculture: a strategic outlook

“…2019; Mo & Poppe 2019) and poor demonstrated efficacy at full commercial scale (Barrett et al . 2020; Overton et al . 2020).…”

“…2015; Barrett et al . 2020; Klebert & Su 2020). Some pressure‐washing systems have been combined with a suction unit, but their collection efficacy remains unclear and their use in Norwegian and Scottish salmon aquaculture is very limited.…”

“…This concern is possibly the strongest driver for biofouling mitigation on pen nets in Norway (Bouwman 2020). However, there is increasing uncertainty and controversy around the perceived interference of biofouling on cleaner fish performance (Eliasen et al 2018;Leclercq et al 2018) as well as the continuation of their use as control agents due to welfare concerns (Hjeltnes et al 2019;Mo & Poppe 2019) and poor demonstrated efficacy at full commercial scale (Barrett et al 2020;Overton et al 2020). (4) Reservoirs for non-indigenous species (NIS).…”

Dynamics of dissolved oxygen inside salmon seacages with lice shielding skirts at two hydrographically different sites

“…Shielding skirts are a form of barrier technology that attempts to keep the infective copepodids out of the cage by rerouting the upper water column around the cage, which has a higher lice density than the deeper levels due to the preferred swimming depth of the louse (i.e. Huse & Holm 1993, Heuch et al 1995, Hevrøy et al 2003, Geitung et al 2019, Barrett et al 2020.…”