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Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
Fish farming or pisciculture involves commercial animal husbandry, breeding of fish, usually for food, in fish tanks or artificial pen (enclosure), enclosures such as fish ponds. It is a particular type of
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
, which is the controlled cultivation and
harvesting Harvesting is the process of gathering a ripe crop from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. On smaller farms with minimal mechanization, harvesting is the most labor- ...
of
aquatic animal An aquatic animal is any animal, whether invertebrate or vertebrate, that lives in water for most or all of its lifetime. Many insects such as mosquitoes, mayflies, dragonflies and caddisflies have aquatic larvae, with winged adults. Aquatic ani ...
s such as fish,
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s, molluscs and so on, in
natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
or pseudo-natural environment. A facility that releases
juvenile fish Fish go through various life stages between fertilization and adulthood. The life of a fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac whic ...
into the wild for
recreational fishing Recreational fishing, also called sport fishing or game fishing, is fishing for leisure, exercise or competition. It can be contrasted with commercial fishing, which is professional fishing for profit; or subsistence fishing, which is fishing ...
or to supplement a species' natural numbers is generally referred to as a
fish hatchery A fish hatchery is a place for artificial breeding, hatching, and rearing through the early life stages of animals—finfish and shellfish in particular.Crespi V., Coche A. (2008) Food and Agriculture Organization of the United Nations (FAO) Gloss ...
. Worldwide, the most important fish
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
produced in fish farming are
carp Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...
,
catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive ...
,
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
and
tilapia Tilapia ( ) is the common name for nearly a hundred species of cichlid fish from the coelotilapine, coptodonine, heterotilapine, oreochromine, pelmatolapiine, and tilapiine tribes (formerly all were "Tilapiini"), with the economically most ...
. Global demand is increasing for dietary fish protein, which has resulted in widespread overfishing in
wild fisheries A wild fishery is a natural body of water with a sizeable free-ranging fish or other aquatic animal (crustaceans and molluscs) population that can be harvested for its commercial value. Wild fisheries can be marine ( saltwater) or lacustrine/r ...
, resulting in significant decrease in
fish stocks Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters (growth, recruitment, mortality and fishing mortality) are traditionally regarded as the significant factors determining the stock's population dyn ...
and even complete depletion in some regions. Fish farming allows establishment of artificial fish
colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...
that are provided with sufficient
feeding Eating (also known as consuming) is the ingestion of food, typically to provide a heterotrophic organism with energy and to allow for growth. Animals and other heterotrophs must eat in order to survive — carnivores eat other animals, herbi ...
, protection from natural
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s and competitive threats, access to
veterinarian A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, vet ...
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 China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
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 in the period 2000–2018, reaching a record 82.1 million tonnes in 2018. Farming
carnivorous fish Predatory fish are hypercarnivorous fish that actively prey upon other fish or aquatic animals, with examples including shark, billfish, barracuda, pike/muskellunge, walleye, perch and salmon. Some omnivorous fish, such as the red-bellied piran ...
such as
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
, however, does not always reduce pressure on wild fisheries, such farmed fish are usually fed
fishmeal Fish meal is a commercial product made from whole wild-caught fish, bycatch and fish by-products to feed farm animals, e.g., pigs, poultry, and farmed fish.R. D. Miles and F. A. Chapman.FA122: The Benefits of Fish Meal in Aquaculture DietsFisheri ...
and
fish oil Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the b ...
extracted from wild
forage fish Forage fish, also called prey fish or bait fish, are small pelagic fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the foo ...
. The 2008 global returns for fish farming recorded by the
FAO The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...
totaled 33.8 million
tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000  kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s worth about US$60 billion.


Major species


Categories

Aquaculture makes use of local
photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
production (extensive) or fish that are fed with external food supply (intensive).


Extensive aquaculture


Intensive aquaculture

In these kinds of systems fish production per unit of surface can be increased at will, as long as sufficient
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, fresh water and food are provided. Because of the requirement of sufficient fresh water, a massive
water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
system must be integrated in the fish farm. One way to achieve this is to combine
hydroponic Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plant ...
horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
and
water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
, 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
environmentalist An environmentalist is a person who is concerned with and/or advocates for the protection of the environment. An environmentalist can be considered a supporter of the goals of the environmental movement, "a political and ethical movement that se ...
s object to this practice. The cost of inputs per unit of fish weight is higher than in extensive farming, especially because of the high cost of
fish feed Manufactured feeds are an important part of modern commercial aquaculture, providing the balanced nutrition needed by farmed fish. The feeds, in the form of granules or pellets, provide the nutrition in a stable and concentrated form, enabling t ...
. It must contain a much higher level of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
(up to 60%) than
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...
feed and a balanced
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
composition, as well. These higher protein-level requirements are a consequence of the higher feed efficiency of aquatic animals (higher feed conversion ratio CR 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 Aeration (also called aerification or aeriation) is the process by which air is circulated through, mixed with or dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration processes create additional surface area in ...
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 ''Clarias'' is a genus of catfishes (order Siluriformes) of the family Clariidae, the airbreathing catfishes. The name is derived from the Greek ''chlaros'', which means lively, in reference to the ability of the fish to live for a long time out ...
'' 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 Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
. The risk of infections by parasites such as fish lice, fungi (''
Saprolegnia ''Saprolegnia'' is a genus of water moulds often called cotton moulds because of the characteristic white or grey fibrous patches they form. Current taxonomy puts ''Saprolegnia'' as a genus of the heterokonts in the order Saprolegniales. Habits ...
'' spp.), intestinal worms (such as
nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...
or
trematodes Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...
), bacteria (e.g., ''
Yersinia ''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of ''Ye ...
'' spp., ''
Pseudomonas ''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able ...
'' spp.), and protozoa (such as
dinoflagellates The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates a ...
) is similar to that in
animal husbandry Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, starti ...
, especially at high population densities. However, animal husbandry is a larger and more technologically mature area of human agriculture and has developed better solutions to pathogen problems. Intensive aquaculture has to provide adequate water quality (oxygen, ammonia, nitrite, etc.) levels to minimize stress on the fish. This requirement makes control of the pathogen problem more difficult. Intensive aquaculture requires tight monitoring and a high level of expertise of the fish farmer. 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 The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the wild have ...
or
koi or more specifically , are colored varieties of the Amur carp ('' Cyprinus rubrofuscus'') that are kept for decorative purposes in outdoor koi ponds or water gardens. Koi is an informal name for the colored variants of ''C. rubrofuscus'' ke ...
), 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. The increased incidences of dangerous viral diseases of koi carp, together with the high value of the fish, has led to initiatives in closed-system koi breeding and growing in a number of countries. Today, a few commercially successful intensive koi-growing facilities are operating in the UK, Germany, and Israel. Some producers have adapted their intensive systems in an effort to provide consumers with fish that do not carry dormant forms of viruses and diseases. In 2016, juvenile Nile tilapia were given a food containing dried ''
Schizochytrium ''Schizochytrium'' is a genus of unicellular eukaryotes in the family Thraustochytriaceae, which are found in coastal marine habitats. They are assigned to the Stramenopiles (heterokonts), a group which also contains kelp and various microalgae ...
'' in place of
fish oil Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the b ...
. 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 acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
s.


Fish farms

Within intensive and extensive aquaculture methods, numerous specific types of fish farms are used; each has benefits and applications unique to its design.


Cage system

Fish cages are placed in lakes, bayous, ponds, rivers, or oceans to contain and protect fish until they can be harvested. The method is also called "off-shore cultivation" when the cages are placed in the sea. They can be constructed of a wide variety of components. Fish are stocked in cages, artificially fed, and harvested when they reach market size. A few advantages of fish farming with cages are that many types of waters can be used (rivers, lakes, filled quarries, etc.), many types of fish can be raised, and fish farming can co-exist with sport fishing and other water uses. Cage farming of fishes in open seas is also gaining in popularity. Given concerns of disease, poaching, poor water quality, etc., generally pond systems are considered simpler to start and easier to manage. Also, the past occurrences of cage-failures leading to escapes, have raised concern regarding the culture of non-native fish species in dam or open-water cages. On August 22, 2017, there was a massive failure of such cages at a commercial fishery in Washington state in
Puget Sound Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected ma ...
, leading to release of nearly 300,000 Atlantic salmon in non-native waters. This is believed to risk endangering the native Pacific salmon species. Marine Scotland has kept records of caged fish escapes since 1999. The have recorded 357 fish escape incidents with 3,795,206 fish escaping into fresh and salt water. One company, Dawnfresh Farming Limited has been responsible for 40 incident and 152,790 Rainbow Trout escaping into freshwater lochs. Though the cage-industry has made numerous technological advances in cage construction in recent years, the risk of damage and escape due to storms is always a concern.
Semi-submersible Semi-submersible may refer to a self-propelled vessel, such as: * Heavy-lift ship, which partially submerge to allow their cargo (another ship) to float into place for transport *Narco-submarine, some of which remained partially on the surface * ...
marine technology is beginning to impact fish farming. In 2018, 1.5 million
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
are in the middle of a year-long trial at Ocean Farm 1 off the coast of
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
. The semi-submersible project is the world's first deep-sea aquaculture project, and includes -high by -diameter pen made from a series of mesh-wire frames and nets. It is designed to disperse wastes better than more conventional farms in sheltered coastal waters, therefore supporting higher fish packing density.


Copper-alloy nets

Recently,
copper alloys Copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion. The best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead. Both of th ...
have become important netting materials in
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
. Copper alloys are
antimicrobial An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...
, that is, they destroy
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
,
viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...
,
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, and other
microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
. In the
marine environment Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...
, the antimicrobial/algaecidal properties of copper alloys prevent
biofouling Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...
, which can briefly be described as the undesirable accumulation, adhesion, and growth of microorganisms, plants,
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
,
tube worms A tubeworm is any worm-like sessility (zoology), sessile invertebrate that anchors its tail to an underwater surface and secretes around its body a mineral tube, into which it can withdraw its entire body. Tubeworms are found among the following t ...
,
barnacles A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...
,
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
, and other organisms. The resistance of organism growth on copper alloy nets also provides a cleaner and healthier environment for farmed fish to grow and thrive. Traditional netting involves regular and labor-intensive cleaning. In addition to its antifouling benefits, copper netting has strong structural and corrosion-resistant properties in marine environments. Copper-zinc brass alloys are deployed in commercial-scale aquaculture operations in Asia, South America, and USA (Hawaii). Extensive research, including demonstrations and trials, are being implemented on two other copper alloys: copper-nickel and copper-silicon. Each of these alloy types has an inherent ability to reduce biofouling, cage waste, disease, and the need for antibiotics, while simultaneously maintaining water circulation and oxygen requirements. Other types of copper alloys are also being considered for research and development in aquaculture operations. In
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
, the traditional cage farming platform is called
kelong A kelong (or kellong) is an offshore platform built predominantly with wood, which can be found in waters off Malaysia, the Philippines and Indonesia. Only a handful remain around Singapore due to rapid urbanisation. Kelongs are built by fisher ...
.


Open net pen system

The open net pens system is a method that takes place in natural waters, such as rivers, lakes, near the coast or offshore. The breeders rear the fish in large cages floating in the water. The fish are living in natural water but are isolated with a net. Because the only barrier separating the fish from the surrounding environment is a net, this allows the water to flow from the ‘natural’ surrounding through the fish farms. The site of the fish farm is crucial for the farm to be a success or not. Before any fish farm is settled, it is highly recommended to be selective with the site location of the farm. The site must be examined on some essential elements. Important conditions on the location are: # A good interchange of water and also a high replacement of bottom water. # At all depths should be a good current condition. This is necessary because the organic particles should be able to be carried away using the current. # A gravel and sand bottom are qualified for fish farming, although bottoms with silt and mud are not qualified. These should be avoided. # A net should be at least or more above the bottom, so depth is important. Despite these important site conditions, the open net pen method was very popular in Norway and China. This is because of the cost friendliness and efficiency of this method.


Negative external effects

Because of the ocean's water flow and other reasons, open net pen culture is seen as a high-risk method for the environment. The flow allows chemicals, parasites, waste and diseases to spread in the enclosed environment, and this is not beneficial for the natural environment. Another negative consequence is the high escape rate of the cultured fish from these open net pens. These escaped fish also pose a high risk to the surrounding ecosystems. The amount of organic waste produced by fish farms is also alarming. A salmon farm in
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
, for instance, is estimated to produce as much organic waste as equivalent to a town of people between 10,000 and 20,000 people each year. Today 50% of the world's seafood is farm-raised.


Irrigation ditch or pond systems

These use
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
ditches or farm ponds to raise fish. The basic requirement is to have a ditch or pond that retains water, possibly with an above-ground irrigation system (many irrigation systems use buried pipes with headers). Using this method, water allotments can be stored in ponds or ditches, usually lined with
bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...
clay. In small systems, the fish are often fed commercial fish food, and their waste products can help fertilize the fields. In larger ponds, the pond grows water plants and algae as fish food. Some of the most successful ponds grow introduced strains of plants, as well as introduced strains of fish. Control of water quality is crucial. Fertilizing, clarifying, and pH control of the water can increase yields substantially, as long as
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
is prevented and oxygen levels stay high. Yields can be low if the fish grow ill from electrolyte stress.


Composite fish culture

The composite fish culture system is a technology developed in India by the
Indian Council of Agricultural Research The Indian Council of Agricultural Research (ICAR) is an autonomous body responsible for co-ordinating agricultural education and research in India. It reports to the Department of Agricultural Research and Education, Ministry of Agriculture. Th ...
in the 1970s. In this system, of both local and imported fish, a combination of five or six fish species is used in a single fish pond. These species are selected so that they do not compete for food among them by having different types of food habitats. As a result, the food available in all the parts of the pond is used. Fish used in this system include
catla Catla (''Labeo catla''), ( bn, কাতলা, translit=kātlā) also known as the major South Asian carp, is an economically important South Asian freshwater fish in the carp family Cyprinidae. It is native to rivers and lakes in northern Indi ...
and
silver carp The silver carp (''Hypophthalmichthys molitrix'') is a species of freshwater cyprinid fish, a variety of Asian carp native to China and eastern Siberia, from the Amur River drainage in the north to the Xi Jiang River drainage in the south. Alt ...
(surface feeders),
rohu The rohu, rui, ruhi or roho labeo (''Labeo rohita'') is a species of fish of the carp family, found in rivers in South Asia. It is a large omnivore and extensively used in aquaculture. Description The rohu is a large, silver-colored fish o ...
(a column feeder), and
mrigal The mrigal carp (''Cirrhinus cirrhosus''), ( bn, মৃগেল, translit=mrigél) also known as the white carp, is a species of ray-finned fish in the carp family. Native to streams and rivers in India, the only surviving wild population is in ...
and
common carp The Eurasian carp or European carp (''Cyprinus carpio''), widely known as the common carp, is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia.Fishbase''Cyprinus carpio'' Linnaeus, 1758/ref>Arkive The ...
(bottom feeders). Other fish also feed on the excreta of the common carp, and this helps contribute to the efficiency of the system which in optimal conditions produces 3000–6000 kg of fish per hectare per year. One problem with such composite fish culture is that many of these fish breed only during monsoon. Even if fish are collected from the wild, they can be mixed with other species, as well. Thus, a major problem in fish farming is the lack of availability of good-quality stock. To overcome this problem, ways have now been worked out to breed these fish in ponds using hormonal stimulation. This has ensured the supply of pure fish stock in desired quantities.


Integrated recycling systems

One of the largest problems with freshwater pisciculture is that it can use a million gallons of water per acre (about 1 m3 of water per m2) each year. Extended
water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
systems allow for the reuse (
recycling Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
) of local water. The largest-scale pure fish farms use a system derived (admittedly much refined) from the
New Alchemy Institute The New Alchemy Institute was a research center that did pioneering investigation into organic agriculture, aquaculture and bioshelter design between 1969 and 1991. It was founded by John Todd, Nancy Jack Todd, and William McLarney. Its purpose wa ...
in the 1970s. Basically, large plastic fish tanks are placed in a greenhouse. A
hydroponic Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plant ...
bed is placed near, above or between them. When tilapia are raised in the tanks, they are able to eat algae, which naturally grow in the tanks when the tanks are properly fertilized. The tank water is slowly circulated to the hydroponic beds, where the tilapia waste feeds commercial plant crops. Carefully cultured microorganisms in the hydroponic bed convert
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
to
nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
s, and the plants are fertilized by the nitrates and
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...
s.Other wastes are strained out by the hydroponic media, which double as an aerated pebble-bed filter. This system, properly tuned, produces more edible protein per unit area than any other. A wide variety of plants can grow well in the hydroponic beds. Most growers concentrate on
herb In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables and other plants consumed for macronutrients, with savory or aromatic properties that are used for flavoring and garnishing food, for medicinal ...
s (e.g.
parsley Parsley, or garden parsley (''Petroselinum crispum'') is a species of flowering plant in the family Apiaceae that is native to the central and eastern Mediterranean region (Sardinia, Lebanon, Israel, Cyprus, Turkey, southern Italy, Greece, Por ...
and
basil Basil (, ; ''Ocimum basilicum'' , also called great basil, is a culinary herb of the family Lamiaceae (mints). It is a tender plant, and is used in cuisines worldwide. In Western cuisine, the generic term "basil" refers to the variety also kno ...
), which command premium prices in small quantities all year long. The most common customers are
restaurant A restaurant is a business that prepares and serves food and drinks to customers. Meals are generally served and eaten on the premises, but many restaurants also offer take-out and food delivery services. Restaurants vary greatly in appearan ...
wholesalers. Since the system lives in a
greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...
, it adapts to almost all temperate climates, and may also adapt to
tropical climate Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of 18 °C (64.4 °F) or higher in the cool ...
s. The main environmental impact is discharge of water that must be salted to maintain the fishes'
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
balance. Current growers use a variety of proprietary tricks to keep fish healthy, reducing their expenses for salt and wastewater discharge permits. Some veterinary authorities speculate that ultraviolet ozone disinfectant systems (widely used for ornamental fish) may play a prominent part in keeping the tilapia healthy with recirculated water. A number of large, well-capitalized ventures in this area have failed. Managing both the biology and markets is complicated. One future development is the combination of integrated recycling systems with urban farming as tried in Sweden by the Greenfish Initiative.


Classic fry farming

This is also called a "flow through system" . Trout and other sport fish are often raised from eggs to fry or fingerlings and then trucked to streams and released. Normally, the fry are raised in long, shallow, concrete tanks, fed with fresh stream water. The fry receive commercial fish food in pellets. While not as efficient as the New Alchemists' method, it is also far simpler and has been used for many years to stock streams with sport fish. European eel (''
Anguilla anguilla The European eel (''Anguilla anguilla'') is a species of eel, a snake-like, catadromous fish. They are normally around and rarely reach more than , but can reach a length of up to in exceptional cases. Eels have been important sources of ...
'') aquaculturalists procure a limited supply of glass eels, juvenile stages of the European eel which swim north from the
Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...
breeding grounds, for their farms. The European eel is threatened with extinction because of the excessive catch of glass eels by Spanish fishermen and overfishing of adult eels in, e.g., the Dutch
IJsselmeer The IJsselmeer (; fy, Iselmar, nds-nl, Iesselmeer), also known as Lake IJssel in English, is a closed off inland bay in the central Netherlands bordering the provinces of Flevoland, North Holland and Friesland. It covers an area of with an a ...
. Although European eel larvae can survive for several weeks, the full life cycle has not yet been achieved in captivity.


Issues


Feeding

The issue of feeds in fish farming has been a controversial one. Many cultured fishes (tilapia, carp, catfish, many others) can be raised on a strictly herbivorous diet. Top-level carnivores (most
salmonidae Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...
species in particular) on the other hand, depend on fish feed, of which a large portion is usually derived from wild-caught fish (
anchovies An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...
,
menhaden Menhaden, also known as mossbunker and bunker and "the most important fish in the sea", are forage fish of the genera ''Brevoortia'' and ''Ethmidium'', two genera of marine fish in the family Clupeidae. ''Menhaden'' is a blend of ''poghaden'' ...
, etc.). Vegetable-derived proteins have successfully replaced fish meal in feeds for carnivorous fishes, but vegetable-derived oils have not successfully been incorporated into the diets of carnivores. Research is underway to try to change this, such that even salmon and other carnivores could be successfully fed with vegetable products. The F3 Challenge (Fish-Free Feed Challenge), as explained by a report from ''
Wired ''Wired'' (stylized as ''WIRED'') is a monthly American magazine, published in print and online editions, that focuses on how emerging technologies affect culture, the economy, and politics. Owned by Condé Nast, it is headquartered in San Fra ...
'' in February 2017, "is a race to sell 100,000 metric tons of fish food, without the fish. Earlier this month, start-ups from places like Pakistan, China, and Belgium joined their American competition at the Google headquarters in Mountain View, California, showing off feed made from
seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
extracts,
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
, and
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
grown in
bioreactor A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, ...
s." Not only do the feeds for carnivorous fish, like certain salmon species, remain controversial due to the containment of wild caught fish like anchovies, but they are not helping the health of the fish, as is the case in Norway. Between 2003 and 2007, Aldrin et al., examined three infectious diseases in Norwegian salmon fish farms—heart and skeletal muscle inflammation, pancreas disease, and infectious salmon anemia. In 2014, Martinez-Rubio et al., conducted a study in which cardiomyopathy syndrome (CMS), a severe cardiac disease in Atlantic salmon (''Salmo salar''), was investigated pertaining the effects of functional feeds with reduced lipid content and increased eicosapentaenoic acid levels in controlling CMS in salmon after infection with Piscine Myocarditis Virus (PMCV). Functional feeds are defined as high-quality feeds that beyond purposes of nutrition, they are formulated with health promoting features that could be beneficial in supporting disease resistance, such as CMS. Choosing a clinical nutrition approach using functional feeds could potentially move away from
chemotherapeutic Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothera ...
and
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
treatments, which could lower the costs of disease treatment and management in fish farms. In this investigation three fishmeal-based diets were served—one made of 31% lipid and the other two made of 18% lipid (one contained fishmeal and the other krill meal. Results demonstrated a significant difference in the immune and inflammatory responses and pathology in heart tissue as the fish were infected with PMCV. Fish fed with functional feeds with low lipid content demonstrated milder and delayed inflammatory response and therefore, less severe heart lesions at earlier and later stages after PMCV infection.


Stocking density

Secondly, farmed fish are kept in concentrations never seen in the wild (e.g. 50,000 fish in a area.). However, fish tend also to be animals that aggregate into large schools at high density. Most successful aquaculture species are schooling species, which do not have social problems at high density. Aquaculturists feel that operating a rearing system above its design capacity or above the social density limit of the fish will result in decreased growth rate and increased feed conversion ratio (kg dry feed/kg of fish produced), which results in increased cost and risk of health problems along with a decrease in profits. Stressing the animals is not desirable, but the concept of and measurement of stress must be viewed from the perspective of the animal using the scientific method.


Parasites and disease

Sea lice Sea lice (singular: sea louse) are copepods (small crustaceans) of the family Caligidae within the order Siphonostomatoida. They are marine ectoparasites (external parasites) that feed on the mucus, epidermal tissue, and blood of host fish. The ...
, particularly ''Lepeophtheirus salmonis'' and various ''Caligus'' species, including ''C. clemensi'' and ''C. rogercresseyi'', can cause deadly infestations of both farm-grown and wild salmon. Sea lice are
ectoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s which feed on mucus, blood, and skin, and migrate and latch onto the skin of wild salmon during free-swimming, planktonic ''nauplii'' and ''copepodid'' larval stages, which can persist for several days. Large numbers of highly populated, open-net salmon farms can create exceptionally large concentrations of sea lice; when exposed in river estuaries containing large numbers of open-net farms, many young wild salmon are infected, and do not survive as a result. Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable. On the
Pacific coast of Canada , settlement_type = List of regions of Canada, Region of British Columbia , image_skyline = , nickname = "The Coast" , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Provinces and ...
, the louse-induced mortality of pink salmon in some regions is commonly over 80%. In Scotland, official figures show that more than nine million fish were lost to disease, parasites, botched treatment attempts and other problems on fish farms between 2016 and 2019. One of the treatments for parasite infestations involved bathing fish in hydrogen peroxide, which can harm or kill farmed fish if they are in a weak condition or if the chemical concentration is too strong. A 2008 meta-analysis of available data shows that salmon farming reduces the survival of associated wild salmon populations. This relationship has been shown to hold for Atlantic, steelhead, pink, chum, and coho salmon. The decrease in survival or abundance often exceeds 50%. Diseases and parasites are the most commonly cited reasons for such decreases. Some species of sea lice have been noted to target farmed coho and Atlantic salmon. Such parasites have been shown to have an effect on nearby wild fish. One place that has garnered international media attention is British Columbia's
Broughton Archipelago Broughton Archipelago is a group of islands located at the eastern end of Queen Charlotte Strait in Mount Waddington Regional District, British Columbia. The archipelago is the traditional territory of the Musgamagw Dzawada'enuxw, Namgis, Ma'am ...
. There, juvenile wild salmon must "run a gauntlet" of large fish farms located off-shore near river outlets before making their way to sea. The farms allegedly cause such severe sea lice infestations that one study predicted in 2007 a 99% collapse in the wild salmon population by 2011. This claim, however, has been criticized by numerous scientists who question the correlation between increased fish farming and increases in sea lice infestation among wild salmon. Because of parasite problems, some aquaculture operators frequently use strong antibiotic drugs to keep the fish alive, but many fish still die prematurely at rates up to 30%. Additionally, other common drugs used in salmonid fish farms in North America and Europe include anesthetic, chemotherapeutic, and anthelmintic agents. In some cases, these drugs have entered the environment. Additionally, the residual presence of these drugs in human food products has become controversial. Use of antibiotics in food production is thought to increase the prevalence of
antibiotic resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. ...
in human diseases. At some facilities, the use of antibiotic drugs in aquaculture has decreased considerably due to vaccinations and other techniques. However, most fish-farming operations still use antibiotics, many of which escape into the surrounding environment. The lice and pathogen problems of the 1990s facilitated the development of current treatment methods for sea lice and pathogens, which reduced the stress from parasite/pathogen problems. However, being in an ocean environment, the transfer of disease organisms from the wild fish to the aquaculture fish is an ever-present risk.


Ecosystem impacts

The large number of fish kept long-term in a single location contributes to
habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
of the nearby areas. The high concentrations of fish produce a significant amount of condensed faeces, often contaminated with drugs, which again affects local waterways. Aquaculture not only impacts the fish on the farm, but it also influences other species, which in return are attracted to or repelled by the farms. Mobile fauna, such as crustaceans, fish, birds, and marine mammals, interact with the process of aquaculture, but the long-term or ecological effects as a result of these interactions is still unknown. Some of these fauna may be attracted or demonstrate repulsion. The attraction/repulsion mechanism has various direct and indirect effects on wild organisms at individual and population levels. The interactions that wild organisms have with aquaculture may have implications on the management of fisheries species and the ecosystem in relation to how the fish farms are structured and organized.


Siting

If aquaculture farms are placed in an area with strong current, pollutants can be flushed out of the area fairly quickly. This helps manage the pollution problem and also aids in overall fish growth. Concern remains that resultant bacterial growth fertilised by fish faeces strips the water of oxygen, reducing or killing off the local marine life. Once an area has been so contaminated, fish farms are typically moved to new, uncontaminated areas. This practice has angered nearby fishermen. Other potential problems faced by aquaculturists include the obtaining of various permits and water-use rights, profitability, concerns about
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
and
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including t ...
depending on what species are involved, and interaction with the
United Nations Convention on the Law of the Sea The United Nations Convention on the Law of the Sea (UNCLOS), also called the Law of the Sea Convention or the Law of the Sea Treaty, is an international agreement that establishes a legal framework for all marine and maritime activities. , 167 c ...
.


Genetic modification

In regards to genetically modified, farmed salmon, concern has been raised over their proven reproductive advantage and how it could potentially decimate local fish populations, if released into the wild. Biologist Rick Howard did a controlled laboratory study where wild fish and GMO fish were allowed to breed. In 1989,
AquaBounty Technologies AquaBounty Technologies is a biotechnology company based in Maynard, Massachusetts, United States. The company is notable for its research and development of genetically modified fish. It aims to create products that aim to increase the productiv ...
developed the
AquAdvantage salmon AquAdvantage salmon is a genetically engineered (GE) fish, a GE Atlantic salmon developed by AquaBounty Technologies in 1989. The typical growth hormone-regulating gene in the Atlantic salmon was replaced with the growth hormone-regulating gen ...
. The concerns and critiques of cultivating this GMO fish in aquaculture are that the fish will escape and interact with other fish ultimately leading to the reproduction with other fishes. However, the FDA, has determined that while net pens would not be the most appropriate to prevent escapes, raising the salmon in Panama waters would effectively prevent escape because the water conditions there would fail to support long-term survival of any escaped salmon. Another method of preventing Aqua Advantage fish from impacting the ecosystems in the case they escape suggested by the FDA was to create sterile triploid females. This way concerns on reproducing with other fishes would be out of the question. The GMO fish crowded out the wild fish in spawning beds, but the offspring were less likely to survive. The colorant used to make pen-raised salmon appear rosy like the wild fish has been linked with retinal problems in humans.


Labeling

In 2005, Alaska passed legislation requiring that any genetically altered fish sold in the state be labeled. In 2006, a ''
Consumer Reports Consumer Reports (CR), formerly Consumers Union (CU), is an American nonprofit consumer organization dedicated to independent product testing, investigative journalism, consumer-oriented research, public education, and consumer advocacy. Founded ...
'' investigation revealed that farm-raised salmon is frequently sold as wild. In 2008, the US
National Organic Standards Board The National Organic Standards Board (NOSB) is an advisory board that makes recommendations to the United States Secretary of Agriculture on organic food and products. Members are appointed by the Secretary and these make recommendations, one of th ...
allowed farmed fish to be labeled as organic provided less than 25% of their feed came from wild fish. This decision was criticized by the advocacy group
Food & Water Watch Food & Water Watch is a Washington, D.C.-based non-governmental organization group with an office also in Los Angeles, California, which focuses on corporate and government accountability relating to food, water, and corporate overreach. Resulting ...
as "bending the rules" about organic labeling. In the European Union, fish labeling as to species, method of production and origin has been required since 2002. Concerns continue over the labeling of salmon as farmed or wild-caught, as well as about the humane treatment of farmed fish. The
Marine Stewardship Council The Marine Stewardship Council (MSC) is a non-profit organization which aims to set standards for sustainable fishing. Fisheries that wish to demonstrate they are well-managed and sustainable compared to the MSC's standards are assessed by a te ...
has established an Eco label to distinguish between farmed and wild-caught salmon, while the
RSPCA The Royal Society for the Prevention of Cruelty to Animals (RSPCA) is a charity operating in England and Wales that promotes animal welfare. The RSPCA is funded primarily by voluntary donations. Founded in 1824, it is the oldest and largest an ...
has established the Freedom Food label to indicate humane treatment of farmed salmon, as well as other food products.


Indoor fish farming

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. One of the drawbacks to recirculating aquaculture systems is the need for periodic water exchanges. However, the rate of water exchange can be reduced through
aquaponics Aquaponics is a food production system that couples aquaculture (raising aquatic animals such as fish, crayfish, snails or prawns in tanks) with hydroponics (cultivating plants in water) whereby the nutrient-rich aquaculture water is fed to hydro ...
, such as the incorporation of hydroponically grown plants and denitrification. Both methods reduce the amount of nitrate in the water, and can potentially eliminate the need for water exchanges, closing the aquaculture system from the environment. The amount of interaction between the aquaculture system and the environment can be measured through the cumulative feed burden (CFB kg/M3), which measures the amount of feed that goes into the RAS relative to the amount of water and waste discharged. The environmental impact of larger indoor fish farming system will be linked to the local infrastructure, and water supply. Areas which are more drought-prone, indoor fish farms might flow out wastewater for watering agricultural farms, reducing the water affliction. From 2011, a team from the
University of Waterloo The University of Waterloo (UWaterloo, UW, or Waterloo) is a public research university with a main campus in Waterloo, Ontario Waterloo is a city in the Canadian province of Ontario. It is one of three cities in the Regional Municipality ...
led by Tahbit Chowdhury and Gordon Graff examined vertical RAS aquaculture designs aimed at producing protein-rich fish species. However, because of its high capital and operating costs, RAS has generally been restricted to practices such as broodstock maturation, larval rearing, fingerling production, research animal production, specific pathogen-free animal production, and caviar and ornamental fish production. As such, research and design work by Chowdhury and Graff remains difficult to implement. Although the use of RAS for other species is considered by many aquaculturalists to be currently impractical, some limited successful implementation of RAS has occurred with high-value product such as
barramundi The barramundi (''Lates calcarifer'') or Asian sea bass, is a species of catadromous fish in the family Latidae of the order Perciformes. The species is widely distributed in the Indo-West Pacific, spanning the waters of the Middle East, South ...
,
sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...
, and live tilapia in the US,
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
s and
catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive ...
in the Netherlands,
trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...
in Denmark and
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
is planned in Scotland and Canada.


Slaughter methods

Tanks saturated with carbon dioxide have been used to make fish unconscious. Their gills are then cut with a knife so that the fish bleed out before they are further processed. This is no longer considered a humane method of slaughter. Methods that induce much less physiological stress are electrical or percussive stunning and this has led to the phasing out of the carbon dioxide slaughter method in Europe.
Victoria Braithwaite Victoria A. Braithwaite (19 July 1967 – 30 September 2019) was a British scientist who was a Professor of Animal Behaviour and Cognition at Pennsylvania State University. She was the first person to demonstrate that fish feel pain, which impa ...
(2010). ''Do fish feel pain?'' Oxford University Press, p. 180


Inhumane methods

According to T. Håstein of the National Veterinary Institute (Oslo, Norway), "Different methods for slaughter of fish are in place and it is no doubt that many of them may be considered as appalling from an animal welfare point of view." A 2004 report by the
EFSA The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...
Scientific Panel on Animal Health and Welfare explained: "Many existing commercial killing methods expose fish to substantial suffering over a prolonged period of time. For some species, existing methods, whilst capable of killing fish humanely, are not doing so because operators don't have the knowledge to evaluate them." Following are some less humane ways of killing fish. * Air asphyxiation amounts to suffocation in the open air. The process can take upwards of 15 minutes to induce death, although unconsciousness typically sets in sooner. * Ice baths or chilling of farmed fish on ice or submerged in near-freezing water is used to dampen muscle movements by the fish and to delay the onset of post-death decay. However, it does not necessarily reduce sensibility to pain; indeed, the chilling process has been shown to elevate
cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
. In addition, reduced body temperature extends the time before fish lose consciousness. * CO narcosis * Exsanguination without stunning is a process in which fish are taken up from water, held still, and cut so as to cause bleeding. According to references in Yue, this can leave fish writhing for an average of four minutes, and some catfish still responded to noxious stimuli after more than 15 minutes. * Immersion in salt followed by gutting or other processing such as smoking is applied to eel.


More humane methods

Proper stunning renders the fish unconscious immediately and for a sufficient period of time such that the fish is killed in the slaughter process (e.g. through exsanguination) without regaining consciousness. * Percussive stunning involves rendering the fish unconscious with a blow on the head. * Electric stunning can be humane when a proper current is made to flow through the fish brain for a sufficient period of time. Electric stunning can be applied after the fish has been taken out of the water (dry stunning) or while the fish is still in the water. The latter generally requires a much higher current and may lead to operator safety issues. An advantage could be that in-water stunning allows fish to be rendered unconscious without stressful handling or displacement. However, improper stunning may not induce insensibility long enough to prevent the fish from enduring exsanguination while conscious. Whether the optimal stunning parameters that researchers have determined in studies are used by the industry in practice is unknown.


Gallery

File:2019-03-16 01 Aquaculture in Chile.jpg, Fish farming in the fjords of southern Chile File:Fish-farms-vietnam.jpg, Houseboat rafts with cages under for rearing fish near
Mỹ Tho Mỹ Tho () is a city in the Tiền Giang province in the Mekong Delta region of South Vietnam. It has a population of approximately 169,000 in 2006 and 220,000 in 2012. It is the regional center of economics, education and technology. The majorit ...
, Vietnam File:Fish-farming-vietnam.jpg, Transport boats moored at fish processing plant, Mỹ Tho File:Zapotec fish farm in Ixtlan Oaxaca.png, Communal Zapotec fish farm in
Ixtlán de Juárez Ixtlán de Juárez is a town and municipality in the Mexican state of Oaxaca about 65 km north of the city of Oaxaca on Federal Highway 175 towards Veracruz. It is part of the Ixtlán District in the Sierra Norte de Oaxaca region. Adminis ...
, Mexico File:Fish farm Skardu.jpg, Fish farming traditionally takes place in purpose-built tanks in the
Skardu , nickname = , motto = , image_skyline = , map_caption = , pushpin_map = Gilgit Baltistan#Pakistan , pushpin_label_position ...
region in northern
Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
. File:Complexo_de_Piscicultura_do_Acre.jpg, Pisciculture Complex, outside Rio Branco, Brazil


See also

*
Aquaculture of catfish Catfish are easy to farm in warm climates, leading to inexpensive and safe food at local grocers. Catfish raised in inland tanks or channels are considered safe for the environment, since their waste and disease should be contained and not spread ...
*
Aquaculture of salmonids The aquaculture of salmonids is the farming and harvesting of salmonids under controlled conditions for both commercial and recreational purposes. Salmonids (particularly salmon and rainbow trout), along with carp, and tilapia are the three most ...
*
Kelong A kelong (or kellong) is an offshore platform built predominantly with wood, which can be found in waters off Malaysia, the Philippines and Indonesia. Only a handful remain around Singapore due to rapid urbanisation. Kelongs are built by fisher ...
* Rice-fish system *
Aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...


References


Further reading

* * * * * * Jhingran VG (1987
''Introduction to Aquaculture''
Nigerian Institute for Oceanography and Marine Research, FAO, Rome. * *


External links


NOAA Aquaculture Website

FAO Fisheries Department
and it

on fisheries and aquaculture
Coastal Alliance for Aquaculture Reform
Coalition of environmental groups, scientists and First Nations opposed to current salmon farming practices
Ethical concerns about the conditions on fish farms

The Pure Salmon Campaign website

Tropical Fish Farming in Florida

Nature's Subsidies to Shrimp and Salmon Farming
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