Fish farming

Fish farming or pisciculture involves raising fish commercially in tanks or enclosures such as fish ponds, usually for food. It is the principal form of aquaculture, while other methods may fall under mariculture. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most important fish species produced in fish farming are carp, tilapia, salmon, and catfish.Houseboat rafts with cages under for rearing fish near Mỹ Tho, VietnamTransport boats moored at fish processing plant, Mỹ ThoCommunal Zapotec fish farm in Ixtlán de Juárez, MexicoFish farming traditionally takes place in purpose-built tanks in the Skardu region in northern Pakistan. Fish farming or pisciculture involves raising fish commercially in tanks or enclosures such as fish ponds, usually for food. It is the principal form of aquaculture, while other methods may fall under mariculture. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Worldwide, the most important fish species produced in fish farming are carp, tilapia, salmon, and catfish. Demand is increasing for fish and fish protein, which has resulted in widespread overfishing in wild fisheries. China provides 62% of the world's farmed fish. As of 2016, more than 50% of seafood was produced by aquaculture. Farming carnivorous fish, such as salmon, does not always reduce pressure on wild fisheries. Carnivorous farmed fish are usually fed fishmeal and fish oil extracted from wild forage fish. The 2008 global returns for fish farming recorded by the FAO totaled 33.8 million tonnes worth about $US 60 billion. Aquaculture makes use of local photosynthetic production (extensive) or fish that are fed with external food supply (intensive). Growth is limited by available food, commonly Zooplankton feeding on pelagic algae or benthic animals, such as crustaceans and mollusks. Tilapia filter feed directly on phytoplankton, which makes higher production possible. Photosynthetic production can be increased by fertilizing pond water with artificial fertilizer mixtures, such as potash, phosphorus, nitrogen, and microelements. Another issue is the risk of algal blooms. When temperatures, nutrient supply, and available sunlight are optimal for algal growth, algae multiply at an exponential rate, eventually exhausting nutrients and causing a subsequent die-off in fish. The decaying algal biomass depletes the oxygen in the pond water because it blocks out the sun and pollutes it with organic and inorganic solutes (such as ammonium ions), which can (and frequently do) lead to massive loss of fish. An alternate option is to use a wetland system, such as that used in the commercial fish farm Veta La Palma, Spain. To tap all available food sources in the pond, the aquaculturist chooses fish species that occupy different places in the pond ecosystem, e.g., a filter algae feeder such as tilapia, a benthic feeder such as carp or [catfish, and a zooplankton feeder (various carps) or submerged weeds feeder such as grass carp. Despite these limitations, significant fish farming industries use these methods. In the Czech Republic, thousands of natural and semi-natural ponds are harvested each year for trout and carp. The large Rožmberk Pond near Trebon, built in 1590, is still in use.