Epidemiological Factors Associated With Caligus rogercresseyi Infection, Abundance, and Spatial Distribution in Southern Chile

Abstract

Sea lice (Caligus rogercresseyi) are external parasites that affect farmed salmonids in Chile, and the scale of their sanitary and economic impact cannot be overstated. Even though space–time patterns suppose parasite aggregation, specific locations related to different infestation levels, as well as their associated factors across the geographic range involved, had not been investigated as of the writing of the present article. The understanding of the effects and factors entailed by the presence of C. rogercresseyi may be deemed a key element of Integrated Pest Management (IPM). In the present study, the multivariate spatial scan statistic was used to identify geographic areas and times of C. rogercresseyi infestation and to estimate the factors associated with such patterns. We used official C. rogercresseyi monitoring data at the farm level, with a set of 13 covariates, to provide adjustment within the analyses. The analyses were carried out for a period of 5 years (2012–2016), and they included three fish species (Salmo salar, Oncorhynchus mykiss, and Oncorhynchus kisutch) in order to assess the consistency of the identified clusters. A retrospective multinomial, spatial, and temporal scan test was implemented to identify farm clusters of either of the different categories of C. rogercresseyi infested farms: baseline, medium, and high, based on the control chemical threshold established by the health authority. The baseline represents adequate farm performance against C. rogercresseyi infestation. Then, production and environmental factors of the medium and high infestation farms were compared with the baseline using regression techniques. The results revealed a total of 26 clusters (p < 0.001), of which 12 correspond to baseline, 1 to medium, and the remaining 13 to high infestation clusters. In general, baseline clusters are detected in a latitudinal gradient on estuarine areas, with increasing relative risks to complex island water systems. There is a spatial structure in specific sites, north of Los Lagos Region and central Aysén Region, with high infestation clusters and epidemic peaks during 2013. In addition, average weight, salmon species, chemotherapeutants, latitude, temperature, salinity, and year category are factors associated with these C. rogercresseyi patterns. Recommendations for an IPM plan are provided, along with a discussion that considers the involvement of stock density thresholds by salmon species and the spatial structure of the efficacy of chemical control, both intended to avoid the advance of resistance and to minimize environmental residues.

The management of the sea lice in Chile: A review

“…This study, however, did not consider the marine currents in the analysis. In contrast, Lepe-L opez et al 44 analysed a dataset over a period of 5 years (2012-2016), and reported that among the epidemiological factors associated with the abundance and spatial distribution of C. rogercresseyi in southern Chile there is a spatial structure in specific sites with a higher infection pressure, in addition to the average fish weight, salmon species, chemical control ingredient, latitude, temperature, salinity, and year class category.…”

“…This study, however, did not consider the marine currents in the analysis. In contrast, Lepe‐López et al 44 analysed a dataset over a period of 5 years (2012–2016), and reported that among the epidemiological factors associated with the abundance and spatial distribution of C. rogercresseyi in southern Chile there is a spatial structure in specific sites with a higher infection pressure, in addition to the average fish weight, salmon species, chemical control ingredient, latitude, temperature, salinity, and year class category. Zalcman et al 45 analysed the data set provided by Sernapesca for the period 2011–2017, and confirmed that many of the factors that were identified as influencing lice abundance in the early years remain important drivers of sea lice abundance over the long term.…”

Heritability of Immunity Traits and Resistance of Atlantic Salmon against the Sea Louse Caligus rogercresseyi

“…These parasites are parasitic copepods of the family Caligidae and mainly represented by two genera, Caligus and Lepeophtheirus . Two of the principal ectoparasite of these genera affecting salmon farming are Caligus rogercresseyi in the southern hemisphere and Lepeophtheirus salmonids in the northern hemisphere [ 3 , 4 ]. The harmful effect of these parasites is widely known; they can seriously damage the skin, increase stress, reduce growth, and cause high mortality [ 5 , 6 , 7 ].…”