A recent article in The Guardian describes how a report shows that "salmon farming is wreaking ruin" on marine ecosystems. This has serious financial costs as well as environmental costs.
The article goes on to explain how salmon farms in Scotland have seen a 4x increase in fish mortality, with sea lice to blame for at least one-fifth of the deaths, and probably more. While producers bear the costs of things like fish mortality and treatments for sea lice, the report also shows that there is a wider impact on the world, particularly environmentally.