Integrated multi-trophic aquaculture (IMTA) provides the byproducts, including waste, from one aquatic species as inputs ( fertilizers , food ) for another. Farmers combines fed aquaculture (eg, fish , shrimp ) with extractive inorganic (eg, seaweed ) and organic extractive (eg, shellfish ), economic stability (improved output, low cost, product diversification and risk reduction) and social acceptability (better management practices). 
Selecting appropriate species and sizing the various populations to provide adequate ecosystem functions and biological processes to achieve a stable balance, mutually benefiting the ecosystem and improving ecosystem health .
Ideally, the co-cultured species each yield valuable commercial “crops”.  IMTA can synergistically increase total output, even if some of the crops yield less than they would, short-term, in a monoculture . 
Terminology and related approaches
“Integrated” refers to intensive and synergistic cultivation, using water-borne nutrient and energy transfer. “Multi-trophic” means different species of different trophic levels , ie, different (but adjacent) links in the food chain . 
IMTA is a specialized form of the age-old practice of aquatic polyculture , which was the co-culture of various species, often without a look at trophic level. In this case, it may be minimally complementary , potentially leading to reduced production of both species and competition for the same food resource. HOWEVER, some traditional systems Such As polyculture of carps in China employee That multiple species occupy niches dans le même pond, or the cultivation of fish That Is integrated with a terrestrial agricultural species , can be regarded forms of IMTA. 
The more general term “Integrated Aquaculture” is used to describe the integration of monocultures through water transfer between culture sysyems.  The terms “IMTA” and “integrated aquaculture” are mainly interchanged. Aquaponics , fractionated aquaculture, integrated agriculture-aquaculture systems, integrated peri-urban-aquaculture systems, and integrated fisheries-aquaculture systems are all variations of the IMTA concept.
Range of approaches
Today, low-intensity traditional / incidental multi-trophic aquaculture is much more common than modern IMTA.  Most are relatively simple, such as fish / seaweed / shellfish.
True IMTA can be land-based, using ponds or tanks, or even open-water marine or freshwater systems. Implementations-have included species combinations  Such As shellfish / shrimp , fish / seaweed / shellfish, fish / seaweed, fish / shrimp and seaweed / shrimp. 
IMTA in open water (offshore cultivation) can be done by using seaweed grows. The buoys / lines are placed next to the fishnets or cages in which the fish grows.  In some tropical countries, some fishes and shrimps, and others may be considered a form of IMTA.  Since 2010, IMTA has been used commercially in Norway, Scotland, and Ireland.
In the future, systems with other components for additional functions, or similar functions and different size brackets of particles, are likely.  Multiple regulatory issues remain open. 
Modern history of land-based systems
Ryther and co-workers created modern, integrated, intensive, land mariculture.   They originated, both theoretically and experimentally, the integrated use of extractive organisms-shellfish, microalgae and seaweeds-in the treatment of household effluents , descriptively and with quantitative results. A domestic wastewater effluent, mixed with seawater, was the nutrient source for phytoplankton , which in turn became food for oysters and clams . They cultivated other organisms in a food chain rooted in the farm’s organic sludge. Dissolved nutrients in the final effluent were filtered by seaweed (mainly Gracilaria andUlva ) biofilters. The value of the original organisms grown on human waste was minimal.
In 1976, Huguenin proposed adaptations to the treatment of intensive aquaculture effluents in both inland and coastal areas.  Tenore followed by integrating their system of carnivorous fish and the macroalgivore abalone . 
In 1977, Hughes-Games  described the first practical marine fish / shellfish / phytoplankton culture, followed by Gordin, et al., In 1981.  By 1989, a semi-intensive (1 kg fish / m -3 ) seabream and gray mullet pond system by the Gulf of Aqaba ( Eilat ) on the Red Sea supported dense diatom populations, great for feeding oysters .   Hundreds of kilos of fish and oysters cultured here were sold. Researchers also quantified the water quality parameters and nutrient budgets in (5 kg fish m -3) green water seabream ponds.   The phytoplankton is maintained in the water and converted to an algal biomass . Experiments with intensive bivalve crops yielded high bivalve growth rates.       This technology is supported by a small farm in southern Israel.
IMTA Promotes economic and environmental sustainability by converting byproducts and uneaten feed from fed organisms into harvestable crops, thereby Reducing eutrophication , and Increasing economic diversification.   
Properly managed multi-trophic aquaculture accelerates growth without detrimental side-effects.     This increases the site’s ability to assimilate the cultivated organisms, thereby reducing negative environmental impacts.
IMTA enables farmers to diversify their output by replacing it with other products. Initial economic research suggests that IMTA can increase profits and can reduce financial risks due to weather, disease and market fluctuations.  Over a dozen studies have investigated the economics of IMTA systems since 1985. 
Typically, carnivorous fish or shrimp occupy IMTA’s higher trophic levels . They excrete soluble ammonia and phosphorus (ortho phosphate ). Seaweeds and similar species can extract these inorganic nutrients directly from their environment.    Fish and shrimp organic nutrients which feed shellfish and feed feeders .   
Species such as shellfish that occupy intermediate trophic levels often play a dual role, both of which filtering organic bottom-level organisms from the water and some ammonia.  Waste feed can also provide additional nutrients; or by direct consumption or via decomposition into individual nutrients. In some projects, the waste nutrients are also gathered and reused in the food given to the fish in cultivation. This can happen by processing the seaweed grown into food. 
Nutrient recovery is a function of technology, harvest schedule, management, spatial configuration, production, species selection, trophic level biomass ratios, natural food availability, particle size, digestibility, season, light, temperature, and water flow.    Since these factors are significantly varied by site and region, recovery efficiency also varies.
In a hypothetical family-scale fish / microalga / bivalve / seaweed farm, based on pilot scale data, at least 60% of nutrient input of commercial products, nearly three times more than in modern net pen farms. One hectare (2.5 acres) were 35 tons (34 long tones, 39 short tones) of seabream, 100 tones (98 long tones, 110 short tones) of bivalves and 125 tones (123 long). tones; 138 short tones) of seaweeds. These results are important for the control of population, and are important for the maintenance of phytoplanton populations.    
Seaweeds’ nitrogen uptake efficiency ranges from 2-100% in land-based systems.  Uptake efficiency in open-water IMTA is unknown. 
Food safety and quality
IMTA systems, which is one of the most important sources of contamination. Mussels and kelp growing adjacent to Atlantic salmon cages in the Bay of Fundy have been monitored since 2001 for contamination by medicines, heavy metals , arsenic , PCBs and pesticides . These concentrations are either always available or not-detectable or established by the Canadian Food Inspection Agency , the United States Food and Drug Administration and European Community Directives.  Taste testers indicate that these mussels are free of “fishy” taste and aroma and could not be distinguished from “wild” mussels. The mussels’ meat yield is significantly higher, reflecting the increase in nutrient availability.  Mussels grown to eat meat are more advantageous because they maintain their meat value. This finding is of particular interest because of the Bay of Fundy, where this research was conducted, produced in the past, and the presence of Paralytic Shellfish Poisoning (PSP) typically restricts the harvest to the winter months. 
Japan, China, South Korea, Thailand, Vietnam, Indonesia, Bangladesh, etc. have co-cultured aquatic species for centuries in marine, brackish and fresh water environments.   Fish, shellfish and seaweeds have been cultured together in bays , lagoons and ponds. Trial and error has improved integration over time.  The proportion of Asian aquaculture production that occurs in IMTA systems is unknown.
After the 2004 tsunami, many of the shrimp farmers in Aceh Province of Indonesia and Ranong Province of Thailand were trained in IMTA. This has been especially important as the mono-culture of marine shrimp has been widely recognized as unsustainable. Production of tilapia, mud crabs, seaweeds, milkfish and mussels have been incorporated. AquaFish Collaborative Research Support Program
Bay of Fundy
Industry, academia and government are collaborating here to expand production to commercial scale.  The current system integrates Atlantic salmon , blue mussels and kelp ; deposit feeders are under consideration. AquaNet (one of Canada’s Networks of Centers of Excellence) funded phase one. The Atlantic Canada Opportunities Agency is funding phase two. The project leaders are Thierry Chopin ( University of New Brunswick in Saint John ) and Shawn Robinson ( Department of Fisheries and Oceans , St. Andrews Biological Station ).   
Pacific SEA-lab is researching and is licensed for the co-cultivation of sandfish , scallops , oysters, blue mussels, urchins and kelp. “SEA” stands for Sustainable Ecological Aquaculture. The project aims to balance four species.The project is headed by Stephen Cross under a British Columbia Innovation Award at the University of Victoria Coastal Aquaculture Research & Training (CART) network. 
The i-mar Research Center  at the Universidad de Los Lagos , in Puerto Montt is working to Reduce the environmental impact of intensive salmon culture. Initial research involved trout, oysters and seaweeds. Present research is focusing on open waters with salmon, seaweeds and abalone. The project leader is Alejandro Buschmann. 
SeaOr Marine Enterprises Ltd.
SeaOr Marine Enterprises Ltd., which operates for several years on the Israeli Mediterranean coast , north of Tel Aviv , cultured marine fish ( gilthead seabream ), seaweeds (Ulva and Gracilaria) and Japanese abalone . Its approach to local biomass, which has been fed to the abalone. It also effectively provides the water to the fishponds and to meet point-source effluent environmental regulations.
PGP Ltd. is a small farm in Southern Israel. It cultures marine fish, microalgae, bivalves and Artemia . Effluents from seabream and seabass collect in sedimentation ponds, where dense populations of microalgae-mostly diatoms -develop . Clams , oysters and sometimes Artemia filtering the microalgae from the water, producing a clear effluent. The farm sells the fish, bivalves and Artemia.
In the Netherlands, Willem Brandenburg of the UR Wageningen (Plant Science Group) has established the first seaweed farm in the Netherlands. The farm is called “De Wierderij” and is used for research. 
Three farms grow seaweeds for feed in abalone effluents in land-based tanks. Up to 50% of re-circulated water passes through the seaweed tanks.  Somewhat uniquely, neither fish nor shrimp included the upper trophic species. The motivation is to avoid over-harvesting natural seaweed beds and red tides, rather than nutrient abatement. These are the results of the collaboration between Irvine and Johnson Cape Abalone and scientists from the University of Cape Town and the University of Stockholm . 
The Scottish Association for Marine Science , in Oban is developing co-cultures of salmon, oysters, sea urchins, and brown and red seaweeds through several projects.     Research and the development of coastal zone management. Researchers include: Mr. Kelly, A. Rodger, L. Cook, S. Dworjanyn, and C. Sanderson.  
IMTA systems in freshwater pond
Indian carps and stinging catfish are cultured in Bangladesh, but the methods could be more productive. The pond and cage cultures are based only on the fish. They did not take advantage of the productivity increases that were included. Expensive artificial feeds are used, especially to supply the fish with protein. Viviparus bengalensis , such as viviparus bengalensis , were simultaneously cultured, thus increasing the available protein. The organic and inorganic wastes produced as a byproduct of culturing could also be minimized by integrating freshwater snail and aquatic plants, such as water spinach , respectively.