Production, mortality, and infectivity of planktonic larval sea lice, Lepeophtheirus salmonis (Krøyer, 1837): current knowledge and implications for epidemiological modelling

Abstract

Current sea louse models attempt to estimate louse burdens on wild and cultured salmon by predicting the production and distribution of lice larvae and estimating the risk of transmission. While physical characteristics of water bodies and weather can be accurately modelled, many aspects of sea lice biology require further parameterization. The aims of this review are (i) to describe current knowledge regarding the production, mortality, and infectivity of planktonic sea lice larvae and (ii) to identify gaps in knowledge and suggest research approaches to filling them. Several major gaps are identified, and those likely to have the greatest impact on infection levels are (i) egg production, viability and hatching success, (ii) predation in plankton and (iii) copepodid infectivity profiles. A key problem identified in current parameter estimates is that they originate from a number of sources and have been determined using a variety of experimental approaches. This is a barrier to the provision of “best” or consensus estimates for use in modelling. Additional and more consistent data collection and experimentation will help to fill these gaps. Furthermore, coordinated international efforts are required to generate a more complete picture of sea louse infections across all regions experiencing problems with sea lice.

The relevance of larval biology on spatiotemporal patterns of pathogen connectivity among open-marine salmon farms

“…Additionally, the ability of water-borne pathogens to infect or infest a host can be influenced by the physical properties of the water they encounter, which can impact the growth, survival, and/or maturation of the pathogen (Brooker et al 2018). For example, viruses will eventually degrade under ultraviolet B exposure (Jacquet and Bratbak 2003); bacterial or fungal pathogens can become spores in unfavourable abiotic conditions, to become infectious later in conditions more suited to their survival (Lennon and Jones 2011); temperature can impact bacterial replication rates and temperature stress can make hosts more susceptible to bacterial infection (Holt et al 1989), and parasitic larvae development and survival rates are dependent on the water salinity and temperature they encounter (Groner et al 2016a;Samsing et al 2016).…”

“…However, Groner et al's 2016 metaanalysis on salinity's impact on sea lice survival found a general trend of decreasing survival with decreasing salinity, with 20 psu resulting in larval death (Groner et al 2016a). The high fecundity and wide larval dispersal capabilities of the sea lice life cycle benefit their overall survival and success (Brooker et al 2018).…”

Health assessment of the cleaner fish ballan wrasse Labrus bergylta from the British south-west coast

“…Supply of Atlantic salmon has increased by 384% since 1995, with a world production of 2248 t in 2016 (FAO 2018); however, production growth in recent years has dropped by 7% (Marine Harvest 2017). The largest concern to the industry has been parasi tic sea lice, namely Lepeophtherius salmonis Krøyer and Caligus spp., estimated to cost the global industry £700 (~€ 950) million annually (Brooker et al 2018b). Widely used chemicals for the removal of lice, such as the orally administered emamectin benzoate, marketed as SLICE ® , and bath-administered hydrogen peroxide H 2 O 2 , are showing reduced efficacy (Jones et al 2013, Helgesen et al 2015, and in recent years attention has shifted to biological control using cleaner fish, in particular wrasse (Labridae spp.)…”

“…Demand for ballan wrasse is largely met by wild-caught fish, although farming of cleaner fish has developed in the last 5 yr, with the production of 118 000 wrasse in the UK in 2016 (Munro & Wallace 2017). Due to long generation times, wild-caught broodstock have been used exclusively in wrasse culture to date (Brooker et al 2018b), and as wrasse farming becomes more common, it is increasingly important to understand the health status of these wild populations which are either directly transferred for deployment on Scottish salmon farms or used as broodstock.…”

Sterilization of sea lice eggs with ultraviolet C light: towards a new preventative technique for aquaculture

“…This study demonstrates that UVC light has the potential to be an effective preventative lice treatment for the salmon farming industry by reducing the abundance of infective copepodid stages exported from farms. Atlantic salmon farms with relatively high numbers of adult female lice can produce an enormous quantity of larvae (150–965 eggs per eggstring:), and thus are likely to contribute the vast majority of copepodids in coastal waters around fish farms . Reducing export of copepodids from farms will result both in considerably lower infestation pressure for adjacent wild salmonid populations and lower farm re‐infestation rates following delousing treatments.…”