According to Large-Scale Fish Farm Production Offsets Environmental Gains, Assessment Finds, an article published by Science Daily:
Industrial-scale aquaculture production magnifies environmental degradation, according to the first global assessment of the effects of marine finfish aquaculture (e.g. salmon, cod, turbot and grouper). This is true even when farming operations implement the best current marine fish farming practices, according to the findings.
It is large-scale aquaculture – fish farming – that cause the most problems. While fish farming is an increasing source of protein for the world, much of the growth in aquaculture is in Asia where less attention is paid to the environmental effects and more to simply increasing production.