As aquaculture has grown, so have concerns about its environmental impact. In fact, aquaculture can be more environmentally damaging than exploiting wild fisheries. Concerns include waste handling, side-effects of antibiotics, competition between farmed and wild animals, and using other fish to feed consumer-desired carnivorous fish. However, research and commercial feed improvements during the 1990s & 2000s have lessened many of these .About 20 percent of mangrove forests have vanished since 1980, partly due to aqua-farming.Fish waste is organic and composed of nutrients necessary in all components of aquatic food webs. In-ocean aquaculture often produces much higher than normal concentrations of fish waste in the water. The waste collects on the ocean bottom, damaging or eliminating bottom-dwelling life. Waste can also decrease dissolved oxygen levels in the water column, putting further pressure on wild animals.
Cultivators often supply their animals with antibiotics to prevent disease. As with livestock, this can accelerate the evolution of bacterial resistance.
Fish can escape, where they can encounter wild fish and dilute wild genetic stocks through interbreeding.Escaped fish can become invasive and therefore can have a damaging environmental impact.
Farming carnivorous fish such as salmon typically increases the pressure on wild fish, because producing one kilo of farmed salmon requires up to six kilo of fish or other protein. Adequate diets for salmon and other carnivorous fish can be formulated from protein sources such as soy, although are concerns about changes in the balance between omega-6 and omega-3 fatty acids.
Other aquaculture "crops" such as seaweed and filter-feeding bivalve mollusks such as oysters, clams, mussels and scallops are relatively benign or even restorative environmentally. Filter-feeders filter pollutants as well as nutrients from the water, improving water quality.Seaweeds extract nutrients such as inorganic nitrogen and phosphorus directly from the water, and filter-feeding mollusks can extract nutrients as they feed on particulates phytoplankton and detritus.
Despite the environmental concerns, profitable aquaculture can funnel money into promoting sustainable practices.New methods lessen the risk of biological and chemical pollution through minimizing fish stress, fallowing netpens, and applying Integrated Pest Management. Vaccines are being used more and more to reduce antibiotic use for disease control.
Onshore recirculating aquaculture systems, facilities using polyculture techniques, and properly-sited facilities (e.g. offshore areas with strong currents) are examples of ways to manage the negative environmental effects.
