There some risks for farmed salmon. They may be fed dangerous anti-oxidants and antibiotics. They may require pesticides, toxic chemicals, and lots of other fish to eat. The farms may pollute. This VIdeo shows potentially dangerous antioxidants being added to the feed mix for the salmon. The Guardian article, talks about the problems of parasitic sea lice and the extreme techniques used to remove the lice. The Florida article talks about the risks of farmed salmon. GMO salmon are used in some salmon farms, and they can esacpe and hybidize with the wild alsmon. Their farms may also release pollution from the feed , pesticides, and antibiotics.
Escaped GMO salmon compete with wild salmon for space and mates. They may spread disease, the way that elk, deer, and cattle ranches do.