I did a lot of research into sewage around the world before being willing to believe my own estimate. Here is one of my articles that details the negative effects on BC's economy from fish farms: http://fishfarmnews.blogspot.ca/2014/03/fish-farm-sewage-dfo-expansions-cost.html.
Look at the Index in October 2014 for past articles on sewage, or cruise 2015 for my articles on sewage cost in BC, as well as low or negative job effects and so on. For an article of mine that details the lopsided revenue picture, with wild fish revenue towering over farmed fish: http://fishfarmnews.blogspot.ca/2015/05/salmonfishing-revenue-towers-over.html.
Here is an article that gives you more references to follow up on the negative costs of fish farming on the economy. It is vastly negative in BC, on sewage cost alone. And the BC Stats article that compares the fishing sectors, noted that all of aquaculture is worth only $61.9 M to the economy while the commercial, processing and sport sector are more than $600 M economic effect, fully 90% of all activity surrounding the fish resource. (For the BC Stats Report: http://fishfarmnews.blogspot.ca/2013/02/sport-fishing-how-we-tack-up-feb-6-2013.html).
When the heavy environmental damage they cause is taken into account, fish farming operations often are found to generate more costs than revenues.
One study found that aquaculture in Sweden’s coastal waters “is not only ecologically but also economically unsustainable.” Another report concluded that fish farming in a Chinese lake is an “economically irrational choice from the perspective of the whole society, with an unequal tradeoff between environmental costs and economic benefits.” Simply put, aquaculture drives heavy ecological harms and these cost society money. In the U.S., fish farming drives hidden costs of roughly $700 million each year – or half the annual production value of fish farming operations.
This article is at this link: http://worldtruth.tv/norwegian-scientists-warn-against-eating-farmed-salmon-everything-you-need-to-know-about-farmed-fish/.