Abstract
Early life stages of Pink salmon (Oncorhynchus gorbuscha) are at risk of exposure to the active ingredients of chemotherapeutant formulations (hydrogen peroxide [HP], azamethiphos [AZ], emamectin benzoate [EB], cypermethrin [CP] and deltamethrin [DM]) used to control sea lice in salmon aquaculture. LC50 values (95% confidence intervals) for acute 48-h water exposures in order of least to most toxic to seawater-adapted pink salmon fry were: HP (227 [138-418] mg/L), EB (1090 [676-2006] µg/L), AZ (80 [52-161] µg/L), CP (5.1 [3.0-10.5] µg/L), and DM (980 [640-1800] ng/L), and in subchronic 10-d lethality sediment exposure tests: EB (2065 [1384-3720] µg/kg), CP (97 [58-190] µg/kg), and DM (1035 [640-2000] ng/kg). Alterations in behaviour varied between chemicals; no chemical attracted pink salmon fry; fish avoided HP to a limited extent at 50 mg/L), as well as EB (300 µg/L), and AZ (50 µg/L). Significant concentration-dependent decreases in olfactory responsiveness to food extract were seen following AZ, CP and DM exposures that occurred at lower concentrations with longer exposure periods (10 µg/L, 0.5 µg/L and 100 ng/L thresholds at 7 d). Following 10-d sediment exposures, olfaction was only affected by CP exposure at 50 µg/kg. Significant decreases in swimming performance (Ucrit) occured for HP, AZ, CP and DM at concentrations as low as 100 mg/L, 10 µg/L, 2 µg/L and 200 ng/L, respectively. This study provides comprehensive data on the lethal and sublethal effects of aquaculture chemotherapeutant exposure in early life stage pink salmon.
Highlights
Farmed salmon in coastal near-shore waters are often densely populated and susceptible to outbreaks of the parasitic sea lice, Lepeophtheirus salmonis and Caligus spp., that are the greatest source of mortality and economic loss at farms, estimated to be $500 million annually worldwide, representing 6 % of product value (Mustafa et al, 2001; Costello, 2009)
Chemical analysis of water samples for hydrogen peroxide, azamethiphos, emamectin benzoate, cypermethrin and deltamethrin on samples within the entire range for each compound resulted in measured concentrations being 87–92% of target concentrations
Chemical analysis of sediment samples for emamectin benzoate, cypermethrin and deltamethrin on samples within the entire range for each compound resulted in measured concentrations being 76–88% of target concentrations
Summary
Farmed salmon in coastal near-shore waters are often densely populated and susceptible to outbreaks of the parasitic sea lice, Lepeophtheirus salmonis and Caligus spp., that are the greatest source of mortality and economic loss at farms, estimated to be $500 million annually worldwide, representing 6 % of product value (Mustafa et al, 2001; Costello, 2009). The predominant management of outbreaks is with anti-sea lice chemotherapeutants (Burridge and Van Geest, 2014). The first anti-sea lice chemotherapeutants were used in 1994 in Atlantic Canada in response to sea lice infestations in New Brunswick (Burridge and Van Geest, 2014). SLICE® (AI: emamectin benzoate) was introduced in 1999 following issues with resistance and poor efficacy in other products, and became the only product fully registered for use in Canada by 2009. Emergency registrations were issued for Salmosan®, Paramove®50 (AI: hydrogen peroxide), and AlphaMax® (AI: deltamethrin). AlphaMax® was not renewed after 2010, while Paramove®50 and Salmosan® were fully registered in 2016 and 2017, respectively (PMRA, 2016; PMRA, 2017). SLICE®, Paramove®50, and Salmosan® are the only products fully registered in Canada
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