Abstract
Screening has revealed that modern-day feeds used in Atlantic salmon aquaculture might contain trace amounts of agricultural pesticides. To reach slaughter size, salmon are produced in open net pens in the sea. Uneaten feed pellets and undigested feces deposited beneath the net pens represent a source of contamination for marine organisms. To examine the impacts of long-term and continuous dietary exposure to an organophosphorus pesticide found in Atlantic salmon feed, we fed juvenile Atlantic cod (Gadus morhua), an abundant species around North Atlantic fish farms, three concentrations (0.5, 4.2, and 23.2 mg/kg) of chlorpyrifos-methyl (CPM) for 30 days. Endpoints included liver and bile bioaccumulation, liver transcriptomics and metabolomics, as well as plasma cholinesterase activity, cortisol, liver 7-ethoxyresor-ufin-O-deethylase activity, and hypoxia tolerance. The results show that Atlantic cod can accumulate relatively high levels of CPM in liver after continuous exposure, which is then metabolized and excreted via the bile. All three exposure concentrations lead to significant inhibition of plasma cholinesterase activity, the primary target of CPM. Transcriptomics profiling pointed to effects on cholesterol and steroid biosynthesis. Metabolite profiling revealed that CPM induced responses reflecting detoxification by glutathione-S-transferase, inhibition of monoacylglycerol lipase, potential inhibition of carboxylesterase, and increased demand for ATP, followed by secondary inflammatory responses. A gradual hypoxia challenge test showed that all groups of exposed fish were less tolerant to low oxygen saturation than the controls. In conclusion, this study suggests that wild fish continuously feeding on leftover pellets near fish farms over time may be vulnerable to organophosphorus pesticides.
Highlights
Norway produces annually about 1.3 million metric tons of Atlantic salmon (Salmo salar) (Ytrestøyl et al, 2015)
Uneaten feed pellets are typically eaten by wild fish that aggregate in large numbers around fish farms (Uglem et al, 2014)
No statistical difference in end weight, length, or growth was observed between the treatment groups, for the 36 fish used for downstream analyses of plasma, liver, and bile parameters (n = 9 per treatment), or the 72 fish used in the hypoxia stress test (n = 18 per treatment)
Summary
Norway produces annually about 1.3 million metric tons of Atlantic salmon (Salmo salar) (Ytrestøyl et al, 2015). Numerous fish species have been observed underneath salmon farms, the most common being Atlantic cod (Gadus morhua), saithe (Pollachius virens), haddock (Melanogrammus aeglefinus), and Atlantic mackerel (Scomber scomber) (Dempster et al, 2009). Environmental hazards of this organic waste include spreading of pathogens from salmon farms to wild fish, spreading of orally administered drugs used against salmon lice, local eutrophication, and oxygen depletion, as well as contaminants in the feeds such as heavy metals and persistent organic pollutants
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