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'Aquaculture' is the cultivation of the natural produce of water (such as fish or shellfish, algae and other aquatic plants). Mariculture is specifically marine aquaculture, and thus is a subset of aquaculture. Some examples of aquaculture include raising catfish and tilapia in freshwater ponds, growing cultured pearls, and farming salmon in net-pens set out in a bay. Fish farming is a common kind of aquaculture. When the waters lowered after river floods some fishes, namely carps, were held in artificial lakes. Their brood were later fed using nymphs and feces from silkworms used for silk production.
The Romans were quite adept in breeding fish in ponds. In Europe it became common again in monasteries during the Middle Ages, since fish was scarce and thus expensive. The 19th century's transportation improvements made fish easily available and inexpensive, even far from the seas, causing a decline in aquaculture.
The current boom started in the 1960s after overfishing caused another price rise. Today, commercial aquaculture exists on a huge scale previously unknown, causing controversy because of its effects on the public waters beyond the boundaries of the pens.
Aquaculture has been one of the fastest growing segments of global food production in recent decades, and has been hailed as an answer to declining wild fish stocks caused largely by overfishing.
Tuna farming in Australia, as well as of other species, has had immense success.
Salmon farming in the Tenth Region of Chile has, for the first time, brought a stable (yet not sustainable) industry to many depressed backwater towns and started a cash flow; previously, the only employment options had been leaving home, relying on the government, subsistence farming, or fishing.
In an unusual arrangement in Hawaii in the United States, aquaculture is carried out with various combinations of Deep Ocean Water (DOW), and Surface Ocean Water (SOW) which is drawn to the surface by the Natural Energy Laboratory of Hawaii as part of research into OTEC renewable energy. This allows fish which require clean cold water to be raised on shore in water drawn from the ocean depths., Canada, Norway, and Chile, salmon and trout farming are one of the fastest-growing forms of agriculture. Salmon farming is not increasing in the United States because of heavy competition from other countries, and higher environmental standards for fish farms in the US. Salmon farming, like other food producing operations such as beef, wheat or tomatoes can impact the environment.
However, the difference between shore farming and fish farming is that shore farming takes place on private land, while fish farming often takes place on the public waters. Organic wastes from fish cages can have a significant effect on water quality and the population structure of organisms, beyond the boundaries of the fish pens, increasing the occurrence of toxic algal blooms. Algal blooms can cause the death of huge numbers of wild fish and other species, and great harm to wild fisheries. Salmon aquaculture has come under increasing scrutiny from environmental nongovernmental organizations (ENGO's). In Canada, salmon farming sites occupy a small portion of the coastal zone areas where they are located. The total area occupied by Canadian salmon farms in British Columbia and the Bay of Fundy in New Brunswick is about 8,900 acres (36 km²) which is less than 0. Still, even though salmon farms occupy only a small percentage of the public waters, scientists have found a significant degradation of the areas where they exist, with lowered oxygen levels, replacement of native seaweeds with invasive seaweeds, increased algal blooms, reduction of wild species, and loss of nursery habitat for wild fish.
Wild Pacific and Atlantic salmon stocks have seen significant declines over the last several decades, before salmon farming operations started. These declines were caused by a combination of factors including climate change, overfishing and freshwater habitat destruction. However, rivers with fish farms have experienced accelerated decline of wild stocks caused by spread of diseases such as infectious salmon anemia, and parasites such as sea lice from farmed to wild salmon.
Concerns have been raised on the East coast that wild Atlantic salmon may interbreed with and catch disease from salmon that escape from farms. Canadian salmon farmers have significantly reduced the escape of their salmon. The evidence shows that the escape of farmed salmon on Canada's west coast poses low risk to Pacific salmon. However, young wild salmon swimming down river to the ocean are free of sea lice parasites before they swim past the salmon farms, and laden with sea lice after they pass the farms.
Many farmed fish species are carnivorous, meaning that other wild fish species must be harvested to maintain the fish farm. For example, herring are used to make salmon feed. Since herring are the backbone of the North Atlantic food chain, increased fishing pressure on their numbers is a serious threat to all other fish species which depend on herring for food. It is argued that fish farms, far from removing the pressure on wild fish stocks, increase it. Others argue that it takes less fish (in the form of the fishmeal component of an aquaculture diet) to produce a unit of table fish through aquaculture than through the natural food web. Fisheries that are based on species lower on the trophic web (such as many species used for fishmeal) are also more resistent to overfishing than typical table fish fisheries.
The fish farm industry is trying to decrease its reliance on fish for fish feed. A portion of the fish meal used in fish feeds comes from the trimmings and discards of commercial species. More studies are being done concerning shifts in feed composition using poultry and vegetable oils as substitutes for fish protein & oil. This use of land based feeds in turn may result in a decrease of the Omega 3 fish oils in the farmed fish.
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