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.

An alternative to outdoor open ocean cage aquaculture, is through the use of a recirculating aquaculture system (RAS). A RAS is a series of culture tanks and filters where water is continuously recycled and monitored to keep optimal conditions year round. To prevent the deterioration of water quality, the water is treated mechanically through the removal of particulate matter and biologically through the conversion of harmful accumulated chemicals into nontoxic ones.
Other treatments such as ultraviolet sterilization, ozonation, and oxygen injection are also used to maintain optimal water quality. Through this system, many of the environmental drawbacks of aquaculture are minimized including escaped fish, water usage, and the introduction of pollutants. The practices also increased feed-use efficiency growth by providing optimum water quality

Fish Feed And Atmosphere Biology

In order to live, animals must have access to food, air and water. They cannot survive if one of these essential elements is missing. If an element is not available in the requisite quantity an animal will not be able to fulfill its natural functions of growth and reproduction. Instead, it will become weak and diseased and will die before reaching its natural age limit.
We all know that game, for instance, can live only in places where the climate and soil provide enough vegetation for food, or, in the case of predatory animals, where there are sufficient other animals present for them to prey upon. There must also be enough water for drinking and air to breathe. Exactly the same law of nature applies to fish.
Some types of fish live mainly on water plants just as cattle live on grass; others live mainly on small animals such as snails, worms and insects, like the birds. There are also predatory fish which prey on other fishes, just as the predatory lion feeds on other animals.
Like other animals, the fish needs air to live. Air consists of a mixture of gases, mainly of oxygen (21 percent) and nitrogen (78 percent). Fish take up oxygen from air dissolved in the water by means of gills. Some fishes, such as the lungfish, have proper lungs; other such as the catfish group, of which the most common is Clarias (barbel), have both gills and accessory breathing organs.

The physiological processes of the body of fish are adapted to the condition of the water, which depends, in turn, on dissolved and suspended matter in it. In their natural state, rivers and lakes have fresh water, the sea has salt water.

Fish are much more comfortable when there's stable high pressure, and tend to feed actively most anywhere within the water column. He also acknowledges the general cycles of high and low pressure and how fish react to them.

"Let's say we're experiencing a prolonged period of high pressure and the fishing has been good. Then a cold front heads our way. Ahead of the front is low pressure. The fish can sense that the barometer is about to drop. So, right before the high begins to dissipate and the barometer falls, the fish respond with a change in feeding patterns. They'll often feed heavily right before the pressure drops. As it does, they become more uncomfortable and feed less aggressively. When the front passes and high pressure moves back in, the fish may not feed aggressively for at least 24 hours, since they're still adjusting.

"However, it's a different story a day or two after a high settles back in. The fish will have had time to stabilize and an intense bite can occur. When the pressure changes again, such as when another front moves in, the cycle repeats itself."