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Impacts

Pressures and impacts of aquaculture depend on farm location, type of cultured organism, methods used, intensity, and the sensitivity or vulnerability of the environment to possible pressures (Jeffrey, 2014). Potential impacts of aquaculture on aquatic ecosystems include the following:

Aquaculture releases oxygen consuming substances and nutrients (as excretory products and uneaten fish food) as well chemical contaminants (e.g. disinfectants, veterinary medicinal products, trace metals) into water. The released pollutants can cause de-oxygenation of the water, causing adverse impacts on the benthic fauna and contributing to local algal blooms and eutrophication. Anti-corrosion materials (e.g. copper, zinc-platted steal) and antifouling paint used in aquaculture systems can leak to the sea from fish cages and ropes, with toxic effects on ecosystems.

Cultured organisms which escape from aquaculture production sites can interbreed and compete with wild stocks as well as introduce pathogen infections. Sea lice infestations, for example, can threaten wild fish populations by reducing the survival and reproduction rates of wild salmonids. A number of studies links the presence of fish farms to the outbreak of lice into the environment, particularly in the case of salmon (EC, 2015b).

Fishponds are also often associated with barriers and hydrological alterations which can adversely affect the upstream and downstream migration of fish and other organisms. The presence of barriers may reduce flow velocity and, thus, support eutrophication effects. Barriers may also disrupt the natural transport of sediment, affecting the stability of river beds and related ecosystems downstream.

Water intakes for aquaculture production are associated with water abstractions that can contribute to decreasing groundwater levels and low flow situations in rivers.

Yet, certain aquaculture practices such as extensive exploitation can also have positive effects on the natural environment. By acting as water reservoirs, aquaculture ponds can help to manage flooding during periods of high rainfall and retain water for irrigation during dry periods. Aquaculture can also serve biodiversity purposes. Net-pen farms, for example, can become aggregating sites for wild fish, and act as small-scaled marine protected areas due to the prohibition of fishing within farm leasehold areas.