Aquaculture problems: Pollution

While many aquaculture systems are closed with no harmful output, open net cage fish farms and land-based fish farms can discharge significant amounts of wastewater containing nutrients, chemicals, and pharmaceuticals that impact on the surrounding environment.

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For example, the nutrients in unused fish feed and fish faeces can cause local algal blooms, or eutrophication. These blooms lead to reduced oxygen in the water, which in turn can lead to the production of ammonia, methane, and hydrogen sulphide, which are toxic to many aquatic species. Reduced oxygen can also directly kill marine life.

In addition, a wide range of chemicals is currently used in the aquaculture industry, mainly pharmaceuticals such as antibiotics and anti-fouling agents such as copper.

Some of these chemicals are toxic to molluscs and crustaceans, and little is known about their broader ecological implications. In some areas, such as Southeast Asia and South America, frequent use of medications has led to increased resistance of the target pathogen to treatment.

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