Fish farming

Fish farming, also known as pisciculture, is the commercial breeding of fish in tanks or special enclosures like ponds. It is a type of aquaculture, which means growing aquatic animals such as fish, crustaceans, and molluscs in controlled environments. The main goal is usually to produce food, with common fish like carp, catfish, salmon, and tilapia being farmed.

A fish farm on the coast of Euboea island, in South Euboean Gulf, Greece

As more people need protein from fish, wild fishing has caused many fish populations to decrease. Fish farming helps by creating artificial colonies where fish can be fed, protected from dangers, and easily collected when needed. This method does not usually harm wild fish populations. China is the largest producer, providing over 60% of the world's farmed fish.

However, farming some fish like salmon can still affect wild fisheries because these fish are often fed food made from wild caught fish. Fish farming can also cause water pollution and spread diseases to wild fish. There are also concerns about the conditions in which the fish are kept. Besides food, fish farming also supplies live fish for aquariums, with most coming from farms in Asia, Europe, Florida, and South America.

Major species

Top 15 cultured fish species by weight, according to FAO statistics for 2013
Species	Environment	Tonnage (millions)	Value (US$ billions)
Grass carp	Freshwater	5.23	6.69
Silver carp	Freshwater	4.59	6.13
Common carp	Freshwater	3.76	5.19
Nile tilapia	Freshwater	3.26	5.39
Bighead carp	Freshwater	2.90	3.72
Catla (Indian carp)	Freshwater	2.76	5.49
Crucian carp	Freshwater	2.45	2.67
Atlantic salmon	Marine	2.07	10.10
Roho labeo	Freshwater	1.57	2.54
Milkfish	Marine	0.94	1.71
Rainbow trout	Freshwater Brackish Marine	0.88	3.80
Wuchang bream	Freshwater	0.71	1.16
Black carp	Freshwater	0.50	1.15
Northern snakehead	Freshwater	0.48	0.59
Amur catfish	Freshwater	0.41	0.55

Categories

Aquaculture uses either local photosynthetic production (extensive) or fish that are fed with external food supply (intensive).

Extensive aquaculture

Intensive aquaculture

See also: Intensive farming

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.

Controlling roes manually

The cost of inputs per unit of fish weight is higher than in extensive farming, especially because of the high cost of fish feed. It must contain a much higher level of protein (up to 60%) than cattle feed and a balanced amino acid composition, as well. These higher protein-level requirements are a consequence of the higher feed efficiency of aquatic animals (higher feed conversion ratio [FCR], that is, kg of feed per kg of animal produced). Fish such as salmon have an FCR around 1.1 kg of feed per kg of salmon whereas chickens are in the 2.5 kg of feed per kg of chicken range. Fish do not use energy to keep warm, eliminating some carbohydrates and fats in the diet, required to provide this energy. This may be offset, though, by the lower land costs and the higher production which can be obtained due to the high level of input control.

Aeration of the water is essential, as fish need a sufficient oxygen level for growth. This is achieved by bubbling, cascade flow, or aqueous oxygen. Catfish in genus Clarias can breathe atmospheric air and can tolerate much higher levels of pollutants than trout or salmon, which makes aeration and water purification less necessary and makes Clarias species especially suited for intensive fish production. In some Clarias farms, about 10% of the water volume can consist of fish biomass.

Very-high-intensity recycle aquaculture systems (RAS, also Recirculating Aquaculture Systems), where all the production parameters are controlled, are being used for high-value species. By recycling water, little is used per unit of production. However, the process has high capital and operating costs. The higher cost structures mean that RAS is economical only for high-value products, such as broodstock for egg production, fingerlings for net pen aquaculture operations, sturgeon production, research animals, and some special niche markets such as live fish.

Raising ornamental coldwater fish (goldfish or koi), although theoretically much more profitable due to the higher income per weight of fish produced, has been successfully carried out only in the 21st century. Today, a few commercially successful intensive koi-growing facilities are operating in the UK, Germany, and Israel.

In 2016, juvenile Nile tilapia were given a food containing dried Schizochytrium in place of fish oil. When compared to a control group raised on regular food, they exhibited higher weight gain and better food-to-growth conversion, plus their flesh was higher in healthy omega-3 fatty acids.

Fish farms

Fish farming, also called pisciculture, is a way to raise fish in tanks or special enclosures like ponds. It is a type of aquaculture, which means growing aquatic animals in controlled places. Fish farms can be set up in many ways, each with its own good points.

Fish cages are put in lakes, rivers, or even the ocean. They hold fish until they are big enough to sell. Cages can be made from many materials and are good because they can use many kinds of water and let fish farmers work with other water activities. But sometimes cages can break and let fish escape, which can be a problem.

Giant gourami is often raised in cages in central Thailand.

In the Philippines, fish pens are used. These are bigger than cages and use the natural bottom of the water as the floor. They are often used to raise milkfish and can cover large areas of water. Fish pens don’t always need extra food because the fish can eat naturally in the water.

Open net pens are another method where fish are kept in large cages in natural water. The water flows through these cages, but this can sometimes let waste and diseases spread. It’s important to choose a good location for these farms to avoid problems.

Some farms use irrigation ditches or ponds to raise fish. These systems store water and can use plants and algae to feed the fish. Keeping the water clean is very important in these systems.

Fish cages in Lake Victoria, Uganda

One special method is called composite fish culture, used in India. It mixes different kinds of fish in one pond so they don’t compete for food. This method can produce a lot of fish but needs careful management.

Integrated recycling systems combine fish farming with growing plants. The waste from the fish helps feed the plants, and the plants clean the water for the fish. This is a very efficient way to farm fish and grow plants together.

Classic fry farming raises young fish, called fry, in tanks until they are big enough to be released into streams. This method has been used for many years to add fish to rivers for people to catch.

Issues

Fish farming, or pisciculture, raises many concerns about the well-being of the fish. Fish feel pain, and when kept in crowded spaces, they can become stressed, injured, or sick. They may not be able to behave naturally, such as building nests or migrating. Overcrowding can also lower water quality and lead to health issues.

Another concern is feeding. Some fish, like salmon, need food made from other fish, which comes from catching wild fish. Researchers are working on new feeds made from plants and other sources to help solve this problem. Keeping too many fish in one place can also stress them and make them more likely to get sick or infected with parasites. These issues can affect both farmed fish and wild fish nearby.

A North American lake trout fishing farm on Lake Titicaca near Copacabana, Bolivia. Since their introduction in the 1930s, trout have been an invasive species endangering the local fish population.

The number of fish kept in farms can harm the environment around them. The waste from so many fish can pollute the water and affect other sea creatures. Placing farms in certain spots can also cause problems, such as using water that might harm local marine life.

Mean eutrophying emissions (water pollution)
of different foods per 100g of protein
Food types	Eutrophying emissions (g PO₄^3-eq per 100g protein)
Beef	365.3
Farmed fish	235.1
Farmed crustaceans	227.2
Cheese	98.4
Lamb and mutton	97.1
Pork	76.4
Poultry	48.7
Eggs	21.8
Groundnuts	14.1
Peas	7.5
Tofu	6.2

Mean greenhouse gas emissions for different food types
Food types	Greenhouse gas emissions (g CO2-Ceq per g protein)
Ruminant meat	62
Recirculating aquaculture	30
Trawling Fishery	26
Non-recirculating aquaculture	12
Pork	10
Poultry	10
Dairy	9.1
Non-trawling fishery	8.6
Eggs	6.8
Starchy roots	1.7
Wheat	1.2
Maize	1.2
Legumes	0.25

Indoor fish farming

Indoor fish farming uses special treatments like ultraviolet light, ozone, and extra oxygen to keep the water clean. This helps reduce problems like fish escaping, using too much water, and pollution that can happen with regular fish farming. These systems also help fish grow better by giving them the best water conditions.

One challenge with these indoor systems is that the water sometimes needs to be changed. But using methods like growing plants together with the fish, called aquaponics, can help lower the need to change water. These plants help clean the water and might even make it so water doesn’t need to be changed at all. The impact on the environment depends on local water supplies and infrastructure. In places where water is scarce, the water from these farms can be used to help grow crops. Researchers have studied ways to stack fish tanks vertically to grow more fish in less space, but these methods can be expensive and are mostly used for special types of fish right now.

Slaughter methods

Main article: Fish welfare at slaughter

There are different ways to prepare fish for food, and some methods cause more stress to the fish than others. In the past, some methods used carbon dioxide to make fish sleepy before cutting their gills, but this is now seen as unfair to the fish. Better ways include using electric shocks or quick blows to the head to make the fish sleepy right away.

Some older methods can be hard on fish. For example, leaving fish out of water for a long time or putting them in very cold water can make them feel pain. These methods are being replaced by quicker, kinder ways to make sure fish feel less stress. Using the right electric current or a quick tap to the head can help keep fish sleepy during the process, making it more fair to them.