Holistic Monitoring of Maine Sea Lice (Lepeoptheirus Salmonis, Kroyer, 1837) Sensitivities to Therapies: Developing a Novel Assay to Examine Lice Behavior

Sea lice (Lepeoptheirus salmonis) present significant economic and animal welfare challenges to salmon aquaculture globally. Chemical delousing agents are used in many countries, with each nation eventually reporting sea lice developing reduced sensitivities to treatments. While some countries have in place sea lice sensitivity monitoring programs, that is not the case in Maine, USA. Although chemical delousing agents are not currently used in Maine, they have been used in the past and are currently used in neighboring Canadian salmon farms. Different bay management areas (BMAs) were sampled during different seasons to determine if there is a seasonal or spatial component to sea lice sensitivities in Maine. Sampling could not be completed for all seasons or BMAs. Using traditional toxicity bioassay methods, lice were exposed to three common chemical delousing agents (emamectin benzoate, hydrogen peroxide, and azamethiphos) to assess their sensitivities to each. It was found that lice in BMA1 had reduced sensitivities to emamectin benzoate. Lice demonstrated sensitivity to azamethiphos. Sea lice initially demonstrated sensitivity to hydrogen peroxide, but after 24 hours post treatment many of the lice had recovered. These variable results highlight the continued need for sea lice sensitivity monitoring in Maine. A monitoring program would help sea lice mitigation strategies on salmon farms. While traditional toxicity bioassays are useful, they are limited in scope in that they do not consider the sublethal effects of chemical delousing agents on copepodid sea lice. Furthermore, previous methods studying sea lice behavior are typically costly or require extensive equipment setups. A novel behavioral method was developed to assess copepodid behavior in response to exposure to naturally derived compounds. Sea lice behaviors observed using this methodology were similar to sea lice foraging behaviors described in previous work. Contrary to what was demonstrated in previous studies and hypothesized in this thesis, sea lice exposed to isophorone did not exhibit increased overall activity levels or a positive chemotaxis towards the olfactory stimulus. This result suggests that isophorone may play a more complex role in the chemical ecology of salmon farms than previously thought. This highlights the need for further study of the chemical ecology of salmon semiochemicals as it is still poorly understood. The sea lice exposed to putrescine decreased overall activity levels and did not display foraging behavior. This result suggests that putrescine may act as a sea lice repellant and warrants further studies. This novel methodology for studying sea lice behavior is financially and technically accessible to all, and thus may prove to be a reliable way to advance sea lice behavior research in the future