The BBC News site has an article about the threat to Northern Ireland's Salmon from the breeding of native fish with fish farm escapees.
More in depth article from marine.ie.
Aswell as fish interbreeding, the threat to the environment from badly managed intesnive farms is immense, the fish are fed a diet of pellets infused with antibiotics, and often pesticides, causing discharges of nutrients and chemicals into the ecosystems surrounding these cages.
The aquaculture industry is very much left to itself to take responsibility for ethical practices, and as would be expected research based on increasing productivity often overshadows research into environmental impact.
I once considered a career in aquaculture even going as far as to do work experience on Maurice Dunlop's trout fishery on the Upper Bann at Tullylish.
He had a hatchery up in the mountains behind Mayobridge outside Newry where the fish were bred. They were very good quality and the hatchery was fed by a small mountain stream, it was a great place.
I did work experience there in February one year spending all day out in the ponds in waders grading fish and driving round the mournes, happy days!
Incidentally one of the best salmon farming operations in the world is on our doorstep Glenarm Salmon are stocked at low density and the conditions they are grown in are as close to natural as is physically possible, with the cages being flushed by strong tidal waters meaning the salmon are fully tailed and firm.