The obvious benefit of salmon farming is a steady supply of healthy, market-ready salmon without the danger of overfishing an area, the damage caused by deep-water netting, or the need to risk lives upon the open water. Wild sea fish populations cannot sustain even today's rate of fishing, let alone the current growth of fish demand. Aquaculture may help meet this growing need. However, as with all attempts to overrule the natural ecology of an area to our benefit, these benefits come with significant unforeseen costs.
Most immediately noticeable is that fish farms pollute their immediate surroundings, with salmon farms being among the worst culprits. Not only does a fish farm regularly flush out the natural wastes of the fish, but also the associated hormones and growth-related antibiotics of the fish farm environment. Thus the effluent from a salmon farm can wreak havoc on the surrounding marine environment and contaminate local water supplies. Nor is this part of the fish farming industry yet regulated adequately - or, in many places, at all.
While most salmon farms are located on the Pacific coast, the species of salmon being bred is Salmo salar, the Atlantic salmon. Escaped fish, bred and raised to artificially faster maturity, have already been observed to be supplanting the slower growing, wild populations: and the genetic mix is not a healthy one. The increased stress on wild populations creates a perfect breeding ground for opportunistic infections and parasites, further stressing the wild populations not only of salmon, but now also of other fish in the area.
It should be noted that many of these effects can be countered through responsible aquaculture practices, including appropriate waste water filtration and flushing under regulations similar to those governing ship ballast. In addition, by moving fish farms further inland, escaped fish will be much less likely to interfere with native populations.