The effects of the aquaculture chemotherapeutant Salmosan ® (active ingredient [a.i.]: azamethiphos) were examined in Pacific spot prawns (Pandalus platyceros) at three temperatures (5, 11, and 17 C). Post-molt prawns were more sensitive to Salmosan ® than intermolt prawns; repeated (3x) 1-hr LC50 values for post-molt prawns ranged from 17 (9.3-31 95% confident intervals) to 40 (25-63) μg/L a.i. while intermolt prawns survived 3 Â 1-hr exposures up to 100 μg/L a.i. Using LC50 values, Salmosan ® was approximately 2.4 times more toxic at 17 versus 5 C. Temperature significantly altered chemosensory and locomotory behaviors in intermolt prawns with the highest activity at the intermediate temperature. Significant decreases in antennule flicking (84 and 104% over controls) were seen at 17 C after 3 Â 1-hr pulse exposures to 50 and 100 μg/L a. i., respectively. Temperature, but not Salmosan ® , affected molting success: at 17 C significantly lower survival was seen during ecdysis (60% of those at 5 C) and at 5 C, molt time was longer (41 ± 3 days) compared to 11 C (34 ± 4 days) or 17 C (21 ± 4 days). Life stage (molt status) and environmental parameters (temperature) alter the effects of Salmosan ® to non-target spot prawns.

Salmon aquaculture is among the fastest growing food-producing industries worldwide, growing from 12,000 tonnes in 1980 to over 3.2 million tonnes by (Asche et al., 2013FAO, 2020). Canada is now the fourth largest producer of farmed salmon behind Norway, Scotland and Chile producing over 100,000 tonnes of farmed salmon in 2019 (DFO, 2018a). This industry relies on permeable open net pen structures placed directly into nearshore coastal waters to hold the salmon (Asche et al., 2013). These open net pens are efficient for rearing salmon as the open transfer of seawater provides exposure to natural fluctuations in water conditions such as salinity, temperature, nutrients and dissolved oxygen.Outbreaks of parasitic sea lice (Lepeophtheirus salmonis and Caligus spp.) are a major issue in open net pen salmon farming worldwide (Costello, 2006;Krkošek et al., 2005). These ectoparasites feed on the host's skin, mucus and underlying tissue, leaving the host fish susceptible to secondary infection and disease (Costello, 2006).Outbreaks of sea lice represent the greatest source of mortality and economic losses to fish farms, causing estimated global losses of $500 million annually, accounting for 6% of product value (Costello, 2009;Mustafa et al., 2001).