Aquaculture is the breeding, rearing and harvesting of fish, shellfish, algae and other organisms including aquatic plants in all types of water environments. Aquatic organisms are farmed for food, pharmaceuticals, food additives, jewelry (pearls), nutraceuticals and cosmetics. Aquaculture systems and environments include freshwater ponds and tanks, freshwater cages, saltwater coastal ponds and tanks, saltwater coastal cage farms. Marine aquaculture is sometimes called mariculture. Aquaculture uses natural resource inputs such as water, energy and feed and requires planning for the dispersion and treatment of farm affluents.
Certain types of aquaculture such as fish farming in cages can have environmental, ecosystem and biodiversity impacts. Modification of habitat through pollution or by habitat conversion of a terrestrial habitat to an aquatic environment are issues of concern in aquaculture. Sustainable agriculture aims to provide a continued supply of farmed aquatic nutrients beneficial for human sustenance without harming ecosystems or exceeding the planet’s ability to renew the natural resources used.
Aquatic animal protein production is more efficient than terrestrial animal protein. Salmon produce twice the amount of protein per unit of protein fed compared with beef and emit less carbon dioxide into the environment. This higher efficiency is due to reduced energy used by poikilothermic (cold-blooded) animals because they do not maintain body temperature and the high number of offspring produced by fish. Less space is needed to produce much more fish compared with beef.
Since the 1980s, aquaculture became the fastest-growing food-production sector globally. In the four decades leading up to 2021, aquaculture surpassed capture fisheries, and now accounts for more than half of fish produced for human consumption.The main species groups in the top 75% of aquaculture production in 2017 included seaweeds, carps, bivalves, tilapia and catfish. The following table shows the global aquaculture production (metric tons) by species group separated by aquatic environment. Data came from the United Nations Food and Agriculture Organization (2019) and was used for this table published in Boyd CE, et al. (2020) Journal of the World Aquaculture Society, 51 (3), pp. 578-633.
The majority of farmed fish and crustaceans depend on an external supply of manufactured feeds. The commercial aquaculture feed sector grew more than three-fold between 2000 to 2017. Commercial aquaculture feeds are mixtures of plant and animal feed ingredients. Feed ingredients include plant oilseed meals, protein concentrates and oils; captured and aquaculture fishery by-products meals and oils; terrestrial animal by-product meals and fats; cereal by-product meals, protein concentrates and oils; and microbiologically produced protein, also known as single-cell proteins (SCP), produced from algae, bacteria and yeast. The aquaculture sector competes with other terrestrial users for feed ingredients, including the pet food sector. Single-cell proteins, insect meal and microalgae have the potential to replace fishmeal and fish oil in aquaculture feed.
The overexploitation of wild forage fish used to produce fishmeal and fish oil for aquaculture feed was a concern around the year 2000. Over the next 20 years aquaculture became more efficient in using marine resources. Between 2000 and 2017 the global production of fed fish tripled while the annual catch of forage fish for production of fishmeal and fish oil decreased from 23 Mt to 16 Mt. Global production of fishmeal from capture fisheries decreased over this time period. During the 2000s, prices for fishmeal and fish oil more than doubled and since 2012 remained higher than plant-based alternatives. Consequently, aquaculture producers reduced the use of fishmeal and fish oil in feed formulations. These ingredients remain important for supplying essential nutrients and the aquaculture sector increased their share of global fishmeal and global fish oil between 2000 and 2016.
Since 2000, there has been an increase in use of alternative protein and oil ingredients in aquaculture feed. In addition, there has been an increase in the sourcing of fishmeal and fish oil from fish-processing wastes and bycatch, the incidental capture of non-target species. Processing technologies also improved to allow increased fishmeal recovery from anchovies and other pelagic fish species.
The shrimp industry decreased use of fishmeal and fish oil in feed by shifting away from black tiger shrimp to the omnivorous whiteleg shrimp. For salmon and trout, a combination of breeding strategies and better-quality feed ingredients allowed feed to contain a higher proportion of plant protein concentrates. Fish trimmings, the parts removed and not consumed by humans, also reduced the use of wild fish in feed. An improved FCR (feed conversion ratio), which is calculated as feed given/animal weight gain, for many species in aquaculture also contributed to a reduced ratio of wild fish inputs to farmed fish output. Globally this fish-in:fish-out ratio (FIFO) was reduced to 0.28 in 2017 in fed aquaculture species from a previous FIFO of 1.9 calculated in 1997.
Conventional animal feed ingredients are used in aquafeed. The share of global animal feed used as aquafeed was about 4%, compared with 40% for poultry, as of 2014. Many terrestrial feed ingredients for aquaculture are by-products from processing of food products, livestock and seafood.
While livestock feed includes grains and oilseeds, carnivorous fish cannot easily digest starch, non-soluble carbohydrates or fibre in these ingredients. Fish are also more sensitive than livestock to antinutrients and toxins in plant protein ingredients. For these reasons plant and land animal protein concentrates go through extra processing steps to increase the nutritional value for fish. Rapeseed (canola) oil, palm oil and poultry fat are common substitutes for a portion of fish oil.
High omega-3 oils from algae or genetically modified oilseeds can be used to reduce fish oil used in salmon feed while maintaining health benefits to consumers. However this replacement is economically inefficient and there is weak consumer acceptance of the use of genetically modified oilseed ingredients.
Aquaculture fish that consume feed in which fishmeal and fish oil are replaced with plant-sourced products have health changes in their gut, immune systems, endocrine systems and maturation, that can increase disease risks. A strain of genetically selected trout was shown to have improved weight gain on fully plant-based protein feeds, the ability to digest plant amino acids in a similarly to fishmeal and do not develop distal enteritis in the intestine on high-soy diets.
As plant-based ingredients have taken a larger share of aquaculture feed, concerns about the environmental effects of using terrestrial crop resources for aquafeed have been raised. It is estimated that 90% of the environmental impact from fed aquaculture production is tied to feed. Studies that model fishmeal replacement with plant-based proteins such as soy protein concentrate used for shrimp and salmon show potential increases in ecotoxicity from fertilizer and pesticides, pressure on freshwater and land resources, more carbon emissions and biodiversity loss form forest clearing. Due to the environmental damages associated with forest conversion to crop production in Brazil, parts of the aquaculture industry banned the use of Brazilian soy in aquafeed.
Prebiotics are nondigestible food ingredients that act as food for probiotics (bacteria) and selectively stimulate growth and/or activity of certain bacteria in the colon in a way the benefits the host. Dietary fibers composed of complex carbohydrates that bypass acidic digestion act as prebiotics. Probiotics are substrates for the fermentation and proliferation of probiotic bacteria. Most prebiotics derive from the cell walls of plants, bacteria or yeast. Common prebiotics used in aquaculture include mannan-oligosaccharides (MOS) and fructo-oligosaccharides (FOS), xylooligosaccharides and galactooligosaccharides. Inulin and glucans are examples of nonstarch polysaccharides that can act as prebiotics. Studies have shown that feeding MOS increased growth performance of fish. MOS are thought to work by stimulating feed intake and nutrient digestibility. Beta-glucans and MOS were shown to improve gut integrity features such as microvilli density and absorption and transport of nutrients across the intestine.
Beta-glucans and MOS supplementation have reduced mortalities in aquaculture fish. There is evidence that fish fed these supplements show an increased immune response. Prebiotics are also thought to promote the proliferation of beneficial bacterial that may directly or indirectly antagonize pathogenic microbes. The characterization of gut microbiota in rainbow trout using next-generation sequencing (NGS) found MOS increased bacterial diversity and changed the abundance of certain species of bacteria. Prebiotics tend to reduce pathogenic bacteria and increase lactic acid bacteria.
Probiotics are living bacteria or yeast which colonize the intestine in a way that benefits the host organism. Live probiotics are given in cold-pressed feeds or added after extrusion so that probiotics are not inactivated by high temperatures and pressure. Probiotics commonly used in aquaculture include the bacteria Bacillus, Enterococcus, Lactobacillus, Lactococcus and Pediococcus as well as brewer’s yeast, Saccharomyces cerevisiae. Most probiotics are gram-positive, lactic acid bacteria of the Lactobacillales order, which have roles in stimulation of the host GI development, digestive function, mucosal tolerance, immune response and disease resistance. Yeast are known to produce beneficial enzymes and antimicrobial pepetides.
Benefits of probiotics in aquaculture species such as Nile tilapia and rainbow trout include increase in growth rate, weight gain and/or feed efficiency. Probiotics enhance metabolic pathways by contributing vitamins, short-chain fatty acids and enzymes that the host does not produce or receive from their diet in sufficient quantities. Young rainbow trout fry that received probiotic yeast showed increased development of the digestive system.
Aquaculture feed additives include amino acids and ingredients that affect metabolism and physiology. Dietary nucleotides are thought to stimulate feed intake and fish feeding behavior and positively influence immune functions.
Enzymes are added to aquaculture feeds to increase digestion of non-starch polysaccharide, reduce negative effects of antinutritional factors or to improve protein digestion. Enzymes used in aquaculture include xylanase, phytase, alpha-galactosidase, cellulase, beta-glucanase and proteases.
Bacterial peptidoglycans are part of the bacterial cells wall. Bacterial peptidoglycans from deactivated bacteria given as a supplement has been shown to stimulate the fish immune system.
Carotenoids in fish feed are widely used as additives to improve muscle and skin coloration in salmonid, shrimp and aquarium fish. Carotenoids may be naturally sourced from green algae, red yeast and crustaceans, or synthetic, such as astaxanthin. Carotenoid supplementation has been reported to enhance growth and immunocompetence in shrimp.
Offshore marine aquaculture, also called open-ocean aquaculture, refers to production systems that are exposed to high energy elements such as wind, waves, storms and currents and that are not protected by land masses. Offshore aquaculture is designed to produce large volumes of fish with minimal land and freshwater constraints, coastal environmental impacts. Technologies developed by other industries such as offshore oil and gas exploitation have been applied to improving cage performance and survivability. Norway and China are leaders in offshore fish aquaculture and they use massive submersible cages. A single Norwegian sea cage can hold up to 200,000 farmed salmon.
Environmental concerns associated with net-pens are related to wastes that accumulate underneath, water pollution, transfer of diseases to and from wild fish and the escape of farmed fish into the wild. Siting farms in water that has an adequate depth and current speed can improve waste dispersion and mitigate some negative effects of offshore marine aquaculture. Feeds that leach less nutrients into the water and that are utilized efficiently by the fish with minimal waste benefit the farmed fish and the surrounding environment. Due to public concern about interactions with the marine environment, potential ecological damage and competing uses of ocean and natural resources, government regulations have put limits on commercial development of offshore aquaculture, particularly in the USA and European Union.
Freshwater aquaculture predominantly consists of household-managed ponds and small-to medium-scale commercial fisheries that produce carps and other fish in polyculture systems for local and regional consumption. Freshwater aquaculture facilities produce tilapia and striped catfish. Freshwater and brackish-water crustaceans such as whiteleg shrimp are produced intensively in monoculture. Polyculture systems combine black tiger shrimp with other fish, molluscs and aquatic plants.
As of 2021, China was the largest producer of freshwater fish and accounted for 56% of global output in 2017. Asia produced 93% of freshwater aquaculture globally as of 2021. The rise in aquaculture production in Asia coincides with urban demand and the decline in wild inland fisheries. Small- to medium-scale aquaculture enterprises in South and Southeast Asia helped to alleviate rural poverty and positively impacted labour and livelihoods in adjacent industries.
Over-intensification and particularly cage aquaculture has resulted in nutrient pollution and production decline due to pathogens. Due to pollution, aquaculture is prohibited in many public water bodies that are essential for drinking water and other ecosystem services.
In-pond raceway systems can enhance efficiency of feed use and removal of sold waste for the farming of channel catfish, carp and tilapia but have not been widely adopted due to high costs.
Recirculating aquaculture systems control all environmental facets of production by continually filtering, treating and reusing water. These systems increase operational efficiency and reduce risks from pathogens, parasites and pests and climate change. Compared with conventional aquaculture, recirculating aquaculture systems require less land and water and enable higher stocking densities. However there are larger energy requirements, production costs, waste disposal challenges and risk of catastrophic disease failures.
Recirculating aquaculture is typically used for broodstock and vulnerable early life stages when advantages in fish performance outweigh the costs. Recirculating aquaculture systems applied within raceways and channelled pond systems for shrimp aquaculture, where they reduce disease and water-quality risks.
Extractive species such as algae and molluscs extract and use organic and inorganic materials and by-products from other species for their own growth. As a proportion of aquacultural output, molluscs and algae comprised 6% and 7.6% respectively of total edible weight in a 2019 report. Algae and molluscs provide ecosystem services and are a source of non-food products.
Bivalves, which include clams, oysters, scallops and mussels, do not require feed inputs. Molluscan aquaculture outputs include seafood as well as industrial products like fertilizers, construction materials, poultry grit, pharmaceuticals and nutraceuticals. Molluscs filter phytoplankton and accumulate nitrogen and phosphorous, removing these nutrients from the environment upon harvesting. Ongoing research is measuring whether bivalves act as a carbon sink or source.
Molluscs assimilate excess nutrients from human activities such as agriculture, aquaculture and sewage discharge. Bivalves can enhance water purification, water clarity and absorb viruses, bacteria, toxic algae and polluted organic particles. Therefor there are high food safety risks for molluscs cultivated in polluted environments. Bivalve cultivation can have negative environmental impacts when overstocked, inappropriately sited or unsustainably managed.
Algae range in size from microscopic species to giant kelps. Macroalgae are commonly referred to as seaweed. Between the years 2000 and 2017 the global production of aquatic plants and algae tripled. More than 97% of that production volume comes from aquaculture. Most algae produce are used in the food industry sector in the form of polysaccharide additives and functional food ingredients and in the non-food sector as hydrocolloid products. Alge-derived hydrocolloids include carrageenan, agar and alginate which are thickening, gelling and emulsifying agents. Hydrocolloid products are mainly used in nutraceuticals, pharmaceuticals and cosmetics. To a lesser extent, hydrocolloid products are used as fertilizers, feed ingredients, biofuels, bioplastics and other industrial outputs.
Evidence is unclear on whether algae consumed by humans could substitute for terrestrial crop and animal protein, fat (omega 3) and energy intake. Variations across algae species, between seasons and coastal environments as well lack of evidence for nutritional bioavailability and metabolic processes have made benefits of algal consumption difficult to quantify. Research suggests microalgal biomass could provide a cost-competitive replacement for fishmeal and in dairy and cattle feed could reduce methane emissions.
Algae has well recognized value for ecosystem services, but financial returns for this value have not been captured by producers. Algae can be used for bioremediation, mitigating ocean acidification, sequestering carbon and enhancing biodiversity. Large-scale seaweed aquaculture shows evidence of reducing nitrogen levels, controlling phytoplankton blooms and limiting the frequency of toxic algal blooms.
Compared with other food sectors, seaweed aquaculture lags behind in breeding, pathogen management and optimization of conditions in production systems. Disease management, such as managing bacterial and viral outbreaks, can account for up to 50% of farm-variable costs for farmed seaweed. In China, the alginate-bearing seaweed, Saccharina japonica (also known as Laminaria japonica) and agar-bearing seaweed (Gracilaria) have successfully been cultivated at scale.
The term integrated aquaculture (IA) has evolved over time. IA is defined as the culture of aquatic organisms based on the sharing of resources that originate from agricultural, agro-industrial, wastewater, power stations and other activities. In the past, IA referred to the combined production of of aquatic and terrestrial organisms, but now can include multiple aquatic organisms without terrestrial organisms. The production of more than one aquatic species is termed polyculture. Polycultures may or may not be integrated systems and this depends on the relationships between the farmed species. Integrated aquaculture systems can produce aquatic organisms with higher efficiency and also reduce environmental impacts. It is possible to configure integrated aquaculture systems to sequester rather than emit carbon.
Integrated multi-trophic aquaculture (IMTA) makes use of waste outputs from one subsystem as an input to another subsystem to create balanced ecosystems. For example, fed species such as finfish or shrimp are combined with organic extractive species like shellfish or herbivorous fish and inorganic extractive species such as seaweed. Finfish is a term used to describe the biological group of fishes that have fins, also called true fishes, which are distinguished from other aquatic life that have common names which also end in fish, such as shellfish. IMTA systems can include open-water, land-based and aquaponics systems. An example of putting IMTA into practice is the transfer by currents of metabolites and uneaten food from salmon in floating net pen ocean culture to adjacently located leafy macro-algae and filter-feeding mollusks, which use these as nutrient sources. Integrated aquaculture also includes Integrated Multi-Niche Aquaculture (IMNA) which is the combined culture of species that occupy different ecological niches within the same trophic level. The integration aims to maximize the use of natural resources and minimize the production of pollutants.
Level 1 production facilities contain more than one species that occupy different spaces. The aquaculture systems that produce both bottom-dwelling organisms (benthic) and those higher in the water column (pelagic species) are Level 1.
Level 2 facilities have species from different ecological niches that occupy similar habitats. For example the silver-carp, which eat phytoplankton, are cultured with big-head carp, which eat zooplankton, and grass-carp, which eat plant material.
Level 3 facilities cultivate one species to improve the environmental conditions for the other species. The water quality can be improved for freshwater prawns when cultures with silver carp and big-head carp at low density.
Level 4 facilities cultivate species that produce by-products used as inputs for cultivation of other species, like in the marine integrated farming of salmon, mussels, holothurians (sea cucumbers) and macroalgae. In this level 4 example, salmon generate particulate organic wastes that are ingested by sea cucumbers and mollusks and dissolved wastes from salmon are absorbed by macroalgae.
Level 5 facilities cultivate multiple species which produce by-products that are inputs for each other. For example, in rice-fish IA systems, leftover rice feeds fish, and their excreted waste serves as fertilizers. Fish and shrimp cultured with rice control plant competitors and insects. Another example is prawn-fish farming in which freshwater prawns feed on feces and leftover food for pelagic fish. The actions of prawns create bioturbation which suspends nutrients, making more plankton available for the fish to eat.
Domestication is the process by which the farmed animal species becomes adapted to humans and the conditions of captivity. Over generations captive animals diverge from their wild ancestors. The levels of domestication for farmed fish are as follows: Level 1 are the first transfer of wild fish into a rearing system. Level 2 is when a portion of the of the life cycle is controlled in captivity, such as control of larval rearing or spawning of breeders. Level 3 has the entire life cycle occurring in captivity, but wild inputs are used to maintain genetic diversity. Level 4 domestication is achieved when wild inputs are no longer used and a genetic barrier between the wild and captive is established. Level 5 adds the application of breeding programs that focus on specific goals. Selective breeding programs initially focused on growth performance, morphology, disease resistance and meat quality. Other traits such as sexual maturity and feed efficiency are selected as well.
According to the Food and Agriculture Organization (FAO) of the United Nations aquaculture production database from 1950 to 2009, 70% of the 250 fish species listed belong to the first three levels of domestication. Domestication appears to contribute to increased production. The 20 most-produced species, globally responsible for 90% of aquaculture production by volume, are within Level 3, 4 or 5. By 2017, Atlantic salmon had been consecutively bred in captivity for over 12 generations in the oldest breeding programs in Norway. Domestication of Atlantic salmon began a few decades ago, but the common carp and Nile tilapia began to be domesticated centuries ago. Thirty species of fish, belonging to 10 families have reached level 5 of domestication. Domesticated species include the common carp, Nile tilapia, rainbow trout, Atlantic salmon, gilthead sea bream, European seabass and turbot.
A sixth level in fish domestication has been proposed for when selection has resulted in strains. Strains have homogeneous appearance, behavior and/or other characteristics which distinguish them from others of the same species, and they can be maintained by propagation. There are few distinct, stable and reproducible strains in aquaculture. Some strains of common carp and rainbow trout are officially registered in some countries. Genetically improved farmed tilapia (GIFT) is a strain developed in the early 1990s that derives from a base population of wild and farmed tilapia from Africa and Asia. The GIFT stain grows 85% faster than the base population tilapia.
Acoustic telemetry technology to measure fish swimming behavior was developed at an experimental fish farm in France. Rainbow trout were fitted with miniature ultrasonic transmitters to monitor fish activity. Fish can also be monitored with sonar and computer-vision technology. Video from submerged cameras and computer-vision algorithms are able to detect fish size and sea-lice infestation.
The Norway-based fish farming company Cermaq established the iFarm project, which uses sensors to monitor individual fish based on their dot patterns. iFarm sensors have the potential to monitor fish numbers, size, sea lice and signs of disease.
Norway Royal Salmon, Microsoft and global technology company, ABB, together developed an artificial intelligence system to monitor salmon in offshore sea cages, allowing safer conditions for workers and fewer boat trips could reduce carbon dioxide emissions.
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Achieving sustainable aquaculture: Historical and current perspectives and future needs and challenges
Claude E. Boyd, Louis R. D'Abramo, Brent D. Glencross, David C. Huyben, Lorenzo M. Juarez, George S. Lockwood, Aaron A. McNevin, Albert G. J. Tacon, Fabrice Teletchea, Joseph R. Tomasso, Craig S. Tucker, Wagner C. Valenti