Shrimp farming, which is usually done in salty coastal waters, has been responsible for the destruction of 38 percent of the world’s mangroves. Growing the soybeans also depends on water availability. To grow the soybeans used in herbivorous and other fish feed, vast areas of South America, almost 4 million hectares of forest, are razed yearly and converted to agricultural land. Land-based closed systems minimize the amount of waste and nutrients expelled to the environment, eliminate fish escapes and limit the spread of disease but pumping the water through them requires a great deal of energy, and the wastewater must still be disposed of properly.įish farming has also resulted in land conversion for feed and the destruction of ecosystems. Most fish farming methods are harmful to the ecosystem in other ways as well. As a result, forage fish are being overfished, and some populations have crashed, which has implications for the entire food web since larger fish depend on them for food. A third of the global fish harvest still goes toward making fish meal and fish oil. In 1997, it took almost 3 tons of forage fish to produce one ton of salmon. This is one reason that fish farming has a reputation as being unsustainable. Over 50 percent of the world’s fish oil is used in feed for farmed salmon. Because salmon and other popular carnivorous fish need omega-3s to grow, 30 to 50 percent of the fish feed traditionally used for these species consists of fishmeal (ground fish) and fish oil. Larger carnivorous fish such as salmon or sea bass then eat the forage fish. Herbivorous fish and forage fish like sardines, anchovies and herring obtain omega-3s by eating the microalgae. Microscopic algae that live in fresh or salt water or sediments produce them. While fish are known for their omega-3 fatty acid benefits, they do not actually produce omega-3s themselves.
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