Closed systems contain the fish and water within the farm rather than releasing them into the environment. In addition, the use of disease-free source water and strict security protocols minimize the spread of disease from farms to the wild. For these reasons, closed systems impact the environment less than open net pens.
All farmed salmon rely on wild-caught fish - in the form of fishmeal or fish oil - for food. U.S. farmed freshwater coho salmon currently require much less wild fish in their feed than do other farmed salmon.