Multivariate evaluation of the effectiveness of delousing treatment efficacy of azamethiphos (Salmosan®) against the salmon louse (Lepeophtheirus salmonis) in Atlantic salmon (Salmo salar) using wellboat, skirt and tarpaulin treatment modalities

Sea lice (Lepeophtheirus salmonis) are the most costly parasitic infestation in the culture of Atlantic salmon (Salmo salar) with control strategies relying heavily on the use of a limited number of chemotherapeutants and traditional univariate analytical tools to evaluate and optimize their delivery. Azamethiphos (Salmosan®) is a powerful delousing agent, which has been administered as a topical treatment using three different modalities: skirt-style enclosures, fully-enclosed tarpaulin enclosures and wellboats. In this study, we analyzed and evaluated the efficacy of azamethiphos treatments between these three modalities against PAAM (pre-adult males and females and, adult males) and adult female (AF) stages using a multivariate approach. The exploratory analysis revealed efficacy in the fully-enclosed tarpaulin modality to be 2.2 times greater compared to skirt-style and wellboat modalities; whereas efficacy against adult females in the wellboat modality was two times larger than in the other modalities. Using the multivariate analysis, treatment efficacy in the fully-enclosed tarpaulin modality was greater than the skirt-style modality, but no significant differences were observed between the wellboat and skirt modalities. These results should be interpreted with caution as differences existed in the abundances and proportions of sea lice stages before treatment that may affect the observed treatment efficacies. For an evaluation and comparison of treatment modalities, multivariate techniques offer added advantages over the more traditional univariate methods, in that simultaneous analysis of multiple sea lice stages and any dependencies or correlation between these stages can be effectively addressed. Statement of relevance: Control of sea lice infestation of Atlantic salmon