Response of Caligus rogercresseyi (Boxshall & Bravo, 2000) to treatment with Hydrogen Peroxide: Recovery of parasites, fish infestation and egg viability under experimental conditions.

Hydrogen peroxide (HP) is used to remove C. rogercresseyi from fish but little is known about its effect on this species. This study determined EC50 and concentration immobilizing 100% of specimens, capacity of parasites exposed to HP to recover and infest fish, and effect on survival into the copepodid stage. EC50 and concentration immobilizing 100% of specimens were estimated by exposing parasites for 20 min to 11 concentrations and evaluating effect at 1 and 24 h post-exposure. Capacity to recover and infest fish, and survival into copepodid were evaluated by exposing parasites and eggs to HP for 20 min. Recovery and fish infestation were evaluated at 25 and 24 h post-exposure, respectively. Eggs were grown until control reached the copepodid stage and survival calculated. EC50 was 709.8 ppm.100% immobilization was obtained at 825 ppm. Male and female recover 0.5 and 1 h post-exposure, respectively. Percentage of parasites exposed and not exposed to HP that were recovered on fish was not significantly different. Survival to copepodid was lower in those exposed to HP. HP effect is greater on copepodids, but 100% of the mobile stages are immobilized under 825 ppm causing detachment from fish and potentially driven away, reducing infestation risk.

Sensitivity assessment of sea lice to chemotherapeutants: Current bioassays and best practices.

Traditional bioassays are still necessary to test sensitivity of sea lice species to chemotherapeutants, but the methodology applied by the different scientists has varied over time in respect to that proposed in "Sea lice resistance to chemotherapeutants: A handbook in resistance management" (2006). These divergences motivated the organization of a workshop during the Sea Lice 2016 conference "Standardization of traditional bioassay process by sharing best practices." There was an agreement by the attendants to update the handbook. The objective of this article is to provide a baseline analysis of the methodology for traditional bioassays and to identify procedures that need to be addressed to standardize the protocol. The methodology was divided into the following steps: bioassay design; material and equipment; sea lice collection, transportation and laboratory reception; preparation of dilution; parasite exposure; response evaluation; data analysis; and reporting. Information from the presentations of the workshop, and also from other studies, allowed for the identification of procedures inside a given step that need to be standardized as they were reported to be performed differently by the different working groups. Bioassay design and response evaluation were the targeted steps where more procedures need to be analysed and agreed upon.

Sensitivity of Caligus rogercresseyi (Boxshall and Bravo 2000) to pyrethroids and azamethiphos measured using bioassay tests-A large scale spatial study.

The variety of antiparasitics that can be used against caligid copepods is limited and efforts are needed to maintain their efficacies. The objective of this study was to monitor the sensitivity of Caligus rogercresseyi, populations towards antiparasitics based on deltamethrin, cypermethrin and azamethiphos within and across geographic regions. The bioassay design consisted of exposing parasites collected from 23 farms to the different chemotherapeutants at the concentration and exposure times recommended for field treatment, under laboratory conditions, and evaluating the number of dead and live parasites 48h after exposure. Parasites were collected from 23 farms distributed in four macrozones in the Los Lagos region and three macrozones in the Aysén region. Parasite sensitivity was evaluated using a Generalized Linear Mixed Model of the Binomial family (Logit) fit by the maximum likelihood, using the lme4 package in R. Parasite gender, macrozone, and antiparasitics were used as fixed factors and farm was the random factor. The model including all the factors proved to be a useful tool for predicting parasite sensitivity. This approach identified (i) those macrozones with a greater likelihood of finding parasite populations which are more or less sensitive to the three antiparasitics, (ii) cases in which parasite sensitivity to the different antiparasitics varied within a given macrozone, (iii) differences in sensitivity between females and males and (iv) an important random effect associated with farm. The results indicate a spatial variability of parasite sensitivity to antiparasitics which, added to the continuous treatments applied on farms, suggest it is necessary to regularly update the sensitivity status in the macrozones. This would allow managers to improve their decision making processes regarding the type of antiparasitic to be used in a given situation. The one-concentration type bioassay performed in this study allowed us to perform a large spatial study with replicated tests of the sensitivity of C. rogercresseyi to pyrethroids and azamethiphos. Further studies should focus on the farm effects, the relationship between the sensitivity of parasites and field efficacy, as well as parasite population structure and connectivity with regard to parasite transmission between farms.