Fish farming or pisciculture involves commercial breeding of fish, most often for food, in fish tanks or artificial enclosures such as fish ponds. It is a particular type of aquaculture, which is the controlled cultivation and harvesting of aquatic animals such as fish, crustaceans, molluscs and so on, in natural or pseudo-natural environments. 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, catfish, salmon and tilapia.

Global demand is increasing for dietary fish protein, which has resulted in widespread overfishing in wild fisheries, resulting in significant decrease in fish stocks and even complete depletion in some regions. Fish farming allows establishment of artificial fish colonies that are provided with sufficient feeding, protection from natural predators and competitive threats, access to veterinarian service, and easier harvesting when needed, while being separate from and thus do not usually impact the sustainable yields of wild fish populations. While fish farming is practised worldwide, China alone provides 62% of the world's farmed fish production. As of 2016, more than 50% of seafood was produced by aquaculture. In the last three decades, aquaculture has been the main driver of the increase in fisheries and aquaculture production, with an average growth of 5.3 percent per year between 2000 and 2018, rising from 32.4 to 82.1 million tonnes.

Farming carnivorous fish such as salmon, however, does not always reduce pressure on wild fisheries, since such farmed fish are usually fed fishmeal and fish oil extracted from wild forage fish. Fish farming is a source of water pollution, and diseases and parasites can spread to wild populations. There are also fish welfare concerns related to overcrowding, which causes stress, injuries, and disease.

Although fish farming for food is the most widespread, another major fish farming industry provides living fish for the aquarium trade. The vast majority of freshwater fish in the aquarium trade originate from farms in Eastern and Southern Asia, eastern Europe, Florida and South America that use either indoor tank systems or outdoor pond systems, while farming of fish for the marine aquarium trade happens at a much smaller scale. In 2022 24% of fishers and fish farmers and 62% of workers in post-harvest sector were women.

Aquaculture makes use of local photosynthetic production (extensive) or fish that are fed with external food supply (intensive).

Extensive aquaculture relies on small or no external inputs of labour and feed, compared to what is being produced. The fish are usually kept in natural bodies of water or artificial ponds and are left to reproduce and feed without much intervention, surviving on the natural resources of where they are kept. This sort of aquaculture is the oldest, and most likely originated in China around 4000 years ago.

Due to this type of aquaculture usually requiring large bodies of water, lakes and ponds may be converted to fish farms. This can pose a threat to local environments, both in terms of the habitats of local species being destroyed, and invasive species being introduced.

In these kinds of systems fish production per unit of surface can be increased at will, as long as sufficient oxygen, fresh water and food are provided. Because of the requirement of sufficient fresh water, a massive water purification system must be integrated in the fish farm. One way to achieve this is to combine hydroponic horticulture and water treatment, see below. The exception to this rule are cages which are placed in a river or sea, which supplements the fish crop with sufficient oxygenated water. Some environmentalists object to this practice.