From small and relatively rare fish aquaculture operations, extensive fish farming grew rapidly from the 1960s across the world: in the Caribbean, South America, the Mediterranean, Norway and Scotland and, by 1985, Australia. As with all intensive farming, the logistics of raising animals in unnatural environments and in high concentrations has produced a multitude of environmental impacts. One of the first, and worst, problems arising was due to salmon pens placed next to wild salmon runs; this seriously threatens the viability of wild-caught salmon, especially since the farmed variety are often carrying diseases such as infectious salmon anemia virus. British Columbia placed a moratorium on new salmon farms to conduct an environmental review and Alaska banned netpen fish farms. Other issues have included: an epidemic of sea lice that caused the collapse of an Irish Sea trout fishery; shrimp farms that collapsed worldwide due to disease; overuse and sometimes illegal use of antibiotics, fish food contaminated with toxic chemicals like PCBs; gross violations of the Clean Water Act in a Maine-based salmon farm in 2003; a patent for transgenic (aka genetically engineered or GE) salmon procured by Canadian researchers.
One of the most treacherous pollutants associated with fish farms is ethoxyquin. Ethoxyquin is found only in farmed salmon — not in wild. Because it prevents fat oxidation, it is used in some animal feeds, including fish food. Ethoxyquin is a chemical developed by Monsanto in the 1950s as a synthetic tyre chemical: it is a rubber stabilizer, pesticide, preservative and antioxidant all in one. The European Food Safety Authority describes it as toxic to aquatic organisms based on the acute toxicity data provided for fish, daphnia and algae. According to a Norwegian newspaper review it is a suspected carcinogen that causes chromosomal aberrations, holes and fractures in chromosomes of human cells, is chemically toxic and destroyed chromosomes and DNA.