Salish Sea Ecosystem Conference

Sublethal effects of the sea lice pesticides ivermectin and SLICE® on starry flounder behaviour and physiology when exposed to contaminated sediments

Aquaculture is an important part of Canada’s economy, and open net-pen Atlantic salmon (Salmo salar) aquaculture is a key facet of this industry. Chemotherapeutants, including anthelminthics, are often used in salmon aquaculture to prevent the loss of stock due to various pathogens. The formulation SLICE® (active ingredient: emamectin benzoate) and ivermectin (IVM) are two chemicals used in salmon aquaculture in Canada to treat and prevent sea lice infestations. SLICE® and IVM have low water solubilities and long half-lives in sediment (225 d and >100 d, respectively). Due to the persistence of these pesticides and their tendency to accumulate in marine sediments, it is crucial to understand the long-term effects of these compounds on wild benthic fauna, including fish. The sublethal effects of these chemotherapeutants on the Pacific benthic teleost Starry Flounder (Platichthys stellatus) using a sediment exposure system were examined. Ecologically relevant endpoints were assessed including: swim performance, growth, aerobic scope, Na+/K+-ATPase activity, metabolites such as glucose and lactate, the whole-tissue metabolome, as well as their camouflage and avoidance behaviour and their ability to perceive and avoid these pesticides. This work employed several novel methods for assessing the effects of chemicals on benthic marine species exposed in sediments, and will contribute to risk estimations that these chemotherapeutants pose to benthic Pacific fish fauna. These findings will also aid in the development of policies, regulations, and guidelines associated with the use of these chemotherapeutants; balancing efforts to minimize sea lice infection rates on the farmed Atlantic salmon and increasing yield, while minimizing risks to benthic species living below open-net pens.