In the United States, approximately 1.3 billion fish are raised in off-shore and land-based aquaculture systems each year for food, making them the second-most commonly farmed animal domestically, following broiler chickens. The majority of farmed fish are subject to overcrowded and restrictive conditions, which, if unchecked, can quickly deteriorate water quality, cause severe stress, and result in increased mortality. Aquaculture practices and production—including handling, grading, transport, genetic manipulation, aggression from conspecifics, predation, physiological stress, and inhumane slaughter—compromise the welfare of these animals.
The Humane Society of the United States, "The Welfare of Animals in the Aquaculture Industry" (2008). IMPACTS ON FARM ANIMALS. 5.