Pesticides that remove salmon lice harm other tiny crustaceans found near fish farms
In aquaculture, bathing fish in pesticides is the most common method to control and remove salmon lice; a small parasitic marine crustacean that attaches to and feeds on farmed and wild salmonids.
We found that hydrogen peroxide, a pesticide used in aquaculture to treat salmon lice, is toxic at concentrations lower than those used in the industry for other small crustaceans found living around salmon farms.
Read this open access paper on the FACETS website.
Although effective, once a hydrogen peroxide bath is completed the waste water is discarded into the ocean which contains a range of small — or planktonic — organisms that are also potentially vulnerable to the pesticide. In the North Atlantic Ocean, you can find salmon farms that use hydrogen peroxide.
You can also find the copepod Calanus spp. — a planktonic crustacean like the salmon louse. Calanus copepods are the most abundant invertebrate and are important to the marine food web.
We wanted to know what concentrations of hydrogen peroxide, if any, kill the copepods. Using concentrations used in aquaculture, we found that 10% of the recommended dose of hydrogen peroxide used to treat salmon lice was lethal to Calanus copepods exposed to the pesticide for one hour.
We also tested what concentrations of the pesticide might not kill the copepods but affect them in a way that they will die from indirect causes, for example, by making them more vulnerable to predation.
We found that 5% of the recommended dose of hydrogen peroxide was enough to paralyze Calanus copepods; in their natural environment the copepods would not be able to successfully escape a predator.
Infestations of salmon lice are a major challenge for the salmon farming industry around the world.
The more we know about how hydrogen peroxide affects planktonic organisms in the ocean the better we can evaluate the impact of aquaculture pesticides on the environment.
Read the full paper — The effects of hydrogen peroxide on mortality, escape response, and oxygen consumption of Calanus spp. by Rosa H. Escobar-Lux, David M. Fields, Howard I. Browman, Steven D. Shema, Reidun M. Bjelland, Ann-Lisbeth Agnalt, Anne Berit Skiftesvik, Ole B. Samuelsen and Caroline M.F. Durif.