Dynamics ofCaligus rogercresseyi(Boxshall & Bravo, 2000) in farmed Atlantic salmon (Salmo salar) in southern Chile: Are we controlling sea lice?

Abstract

Caligus rogercresseyi generates the greatest losses in the salmon industry in Chile. The relationship between salmon farming and sea lice is made up of various components: the parasite, host, environment and farming practices, which make it difficult to identify patterns in parasite population dynamics to define prevention and control strategies. The objectives of this study were to analyse and compare the effect of farming, sanitary practices and environmental variables on the abundance of gravid females (GF) and juveniles (JUV) of C. rogercresseyi on Salmo salar in three Salmon Neighborhood Areas (SNAs) in Region 10, south of Chile. Linear mixed-effects models of the negative binomial distribution were used to evaluate the effect of the different explanatory variables on GF and JUV. Productive variables were the key drivers explaining the abundance of GF and JUV. Results suggest that C. rogercresseyi is not controlled and JUV are persistent in the three SNAs, and sanitary practices do not control the dissemination of the parasite among sites. Environmental variables had a low impact on sea lice abundance. There is a need to perform analysis for modelling of parasite population dynamics to improve Integrated Pest Management, including changes in the governance to achieve an effective prevention and control.

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

“…The density-dependent relationship between sea lice copepods and the concentration of susceptible hosts has been proposed previously ( 8 ). Our finding on the positive effect of biomass in C. rogercresseyi occurrence is consistent with those of different authors ( 1 , 19 , 24 , 26 , 43 , 46 – 49 ) who suggest that it is necessary to set up a maximum level infield practice about fish density per water unit area, predisposing host susceptibility to confinement and stress increases. Bravo et al ( 14 ) propose that a density >10 kg/m 3 increases local C. rogercresseyi abundances; nevertheless, it is not clear whether this estimate can be applied to the growing trend of this economic activity.…”

“…These clusters are, spatially speaking, on the coastline, mainly in estuarine areas. This fact is consistent with the modeling of the parasitic dynamics by Mancilla-Schulz et al ( 19 ), who compared three production sites of Region X [Los Lagos] during the years 2012–2015 and observed that the site with lower salinities presented lower C. rogercresseyi abundances. The tolerance of C. rogercresseyi at low salinities is according to that reported by Bravo et al ( 12 ), who proves a sensitivity to salinities <20 ppt.…”

“…According to the dynamics of infectious diseases ( 18 ), C. rogercresseyi patterns are heterogeneous in space and time. A recent study, limited to three epidemiological neighborhoods with a persistent history of C. rogercresseyi infestation on northern Region X [Los Lagos] during 2012–2015, suggests temporal patterns with high peaks in one specific site exclusively during 2013 ( 19 ). Space–time patterns suppose parasitic aggregation across the geographic area occupied by salmon farming, with an increase in risk around predetermined sites.…”

A low‐cost screening system for kinetic analysis of Caligus rogercresseyi : New focus on pharmacological study of caligidosis disease

“…However, these strategies have not eradicated the parasite. There are also several bioassay types aimed at studying infection phenotypes (Bethke et al, 2017; Lozano et al, 2017) and observing their characteristics (Lozano et al, 2017), clinical studies (Whyte et al, 2014) and trials to observe infection and mechanism of infection (Mordue & Birkett, 2009), but these strategies have also failed to control the disease (Mancilla‐Schulz et al, 2019). In current conditions, all studies are made in vivo, using special hatchlings with high cost and long test times.…”

A simple modelling tool for assessing interaction with host and local infestation of sea lice from salmonid farms on wild salmonids based on processes operating at multiple scales in space and time

“…A key factor limiting aquaculture expansion, is the local density of the salmon louse, Lepeophtheirus salmonis, whose impact is critical to the sustainability of aquaculture . L. salmonis is a major problem in most northern hemisphere marine production (Jones and Beamish 2011), and in Chile the louse Caligus rodgercressyi causes similar problems (Mancilla-Schulz et al 2019). Lice present a major problem to farming of salmon as their control is expensive, costing about 9% of farm revenues (Abolfia et al 2017) and they can cause welfare and other problems.…”