Integrated Multi-Trophic Aquaculture

Integrated Multi-Trophic Aquaculture

Integrated Multi-Trophic Aquaculture (IMTA) is a practice in which the by-products (wastes) from one species are recycled to become inputs (fertilizers, food) for another. Fed aquaculture (e.g. fish, shrimp) is combined with inorganic extractive (e.g. seaweed) and organic extractive (e.g. shellfish) aquaculture to create balanced systems for environmental sustainability (biomitigation), economic stability (product diversification and risk reduction) and social acceptability (better management practices). Chopin T, Buschmann AH, Halling C, Troell M, Kautsky N, Neori A, Kraemer GP, Zertuche-Gonzalez JA, Yarish C and Neefus C. 2001. Integrating seaweeds into marine aquaculture systems: a key toward sustainability. Journal of Phycology 37: 975-986.]

IMTA versus Polyculture

"Multi-Trophic" refers to the incorporation of species from different trophic or nutritional levels in the same system. Chopin T. 2006. Integrated multi-trophic aquaculture. What it is, and why you should care… and don’t confuse it with polyculture. Northern Aquaculture, Vol. 12, No. 4, July/August 2006, pg. 4.] This is one potential distinction from the age-old practice of aquatic polyculture, which could simply be the co-culture of different fish species from the same trophic level. In this case, these organisms may all share the same biological and chemical processes, with few synergistic benefits, which could potentially lead to significant shifts in the ecosystem. Some traditional polyculture systems may, in fact, incorporate a greater diversity of species, occupying several niches, as extensive cultures (low intensity, low management) within the same pond. The "Integrated" in IMTA refers to the more intensive cultivation of the different species in proximity of each other (but not necessarily right at the same location), connected by nutrient and energy transfer through water.

Ideally, the biological and chemical processes in an IMTA system should balance. This is achieved through the appropriate selection and proportions of different species providing different ecosystem functions. The co-cultured species should be more than just biofilters; they should also be harvestable crops of commercial value. A working IMTA system should result in greater production for the overall system, based on mutual benefits to the co-cultured species and improved ecosystem health, even if the individual production of some of the species is lower compared to what could be reached in monoculture practices over a short term period. Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M and Yarish C. 2004. Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture. Aquaculture 231: 361-391.]

Sometimes the more general term "Integrated Aquaculture" is used to describe the integration of monocultures through water transfer between organisms. For all intents and purposes however, the terms "IMTA" and "integrated aquaculture" differ primarily in their degree of descriptiveness. These terms are sometimes interchanged. Aquaponics, fractionated aquaculture, IAAS (integrated agriculture-aquaculture systems), IPUAS (integrated peri-urban-aquaculture systems), and IFAS (integrated fisheries-aquaculture systems) may also be considered variations of the IMTA concept.

IMTA systems

. While IMTA likely occurs due to traditional or incidental, adjacent culture of dissimilar species in some coastal areas, deliberately designed IMTA sites are, at present, less common. Moreover, they are presently simplified systems, like fish/seaweed/shellfish. In the future, more advanced systems with several other components for different functions, or similar functions but different size brackets of particles, will have to be designed. There are also a number of regulatory issues that will have to be addressed. Chopin T, Robinson S, Sawhney M, Bastarache S, Belyea E, Shea R, Armstrong W, Stewart and Fitzgerald P. 2004. The AquaNet integrated multi-trophic aquaculture project: rationale of the project and development of kelp cultivation as the inorganic extractive component of the system. Bulletin of the Aquaculture Association of Canada. 104(3): 11-18.]

Modern history of land-based IMTA

The inception of modern integrated intensive mariculture on land has been the work of Ryther and co-workers Goldman JC, Tenore RK, Ryther HJ and Corwin N. 1974. Inorganic nitrogen removal in a combined tertiary treatment - marine aquaculture system: I. Removal efficiencies. Water Research 8: 45-54.] Ryther JH, Goldman JC, Gifford JE, Huguenin JE, Wing AS, Clarner JP, Williams LD andLapointe BE. 1975. Physical models of integrated waste recycling - marine polyculture systems. Aquaculture 5: 163-177.] who approached, both scientifically and quantitatively, the integrated use of extractive organisms - shellfish, microalgae and seaweeds - in the treatment of household effluents. They described the concept and provided quantitative experimental results of integrated waste-recycling marine aquaculture systems. A domestic wastewater effluent, mixed with seawater, was the source of nutrients for phytoplankton culture, which in turn was fed to oysters and clams. Other organisms were cultured in a separate food chain, based on the organic sludge of the farm. Dissolved remnants of nutrients in the final effluent were filtered by seaweed (mainly Gracilaria and Ulva) biofilters. The weakness of this approach was the questionable value of organisms grown on human waste effluents. Adaptations of this principle to the treatment of intensive aquaculture effluents in both inland and coastal areas was proposed, Huguenin JH. 1976. An examination of problems and potentials for future large-scale intensive seaweed culture systems. Aquaculture 9: 313-342.] and quickly followed by the integration to their system of carnivorous fish and the macroalgivore abalone. Tenore KR. 1976. Food chain dynamics of abalone in a polyculture system. Aquaculture 8: 23–27.]

What is arguably the first practical and quantitative integrated land-based cultures of marine fish and shellfish; including phytoplankton as both the biofilter and shellfish food, were described by Hughes-Games (1977) Hughes-Games WL. 1977. Growing the Japanese oyster (Crassostrea gigas) in sub-tropical seawater fishponds: I. Growth rate, survival and quality index. Aquaculture 11: 217-229.] and Gordin et al. (1981) Gordin H, Motzkin F, Hughes-Games A and Porter C. 1981. Seawater mariculture pond - an integrated system. European Aquaculture Society Special Publication 6: 1-13.] . A semi-intensive (1 kg fish m-3) "green-water" seabream and grey mullet pond system on the coast of the Gulf of Aqaba (Eilat), on the Red Sea, supported dense populations of diatoms, excellent for feeding oysters. Neori A, Krom MD, Cohen Y and Gordin H. 1989. Water quality conditions and particulate chlorophyll a of new intensive seawater fishpond in Eilat, Israel: daily and dial variations. Aquaculture 80: 63-78.] Erez J, Krom MD and Neuwirth T. 1990. Daily oxygen variations in marine fish ponds, Eilat, Israel. Aquaculture 84: 289-305.] Hundreds of kg of fish and oysters cultured in this experiment were actually sold. Neori et al. (1989) and Krom and Neori (1989) Krom MD and Neori A. 1989. A total nutrient budget for an experimental intensive fishpond with circularly moving seawater. Aquaculture 88: 345-358.] quantified the water quality parameters and the nutrient budgets in more intensive (5 kg fish m-3) green water seabream ponds. For the most part, the phytoplankton in their ponds maintained a reasonable water quality and converted on average over half the waste nitrogen into algal biomass. The development of a practical intensive culture of bivalves in these phytoplankton-rich effluents, and the extremely fast bivalve growth rates achieved under these conditions, were described in a series of papers (Shpigel and Friedman, 1990; Shpigel M and Fridman R. 1990. Propagation of the Manila clam Tapes semidecussatus in the effluent of marine aquaculture ponds in Eilat, Israel. Aquaculture 90: 113-122.] Shpigel and Blaylock, 1991; Shpigel M and BlaylockRA. 1991. The Pacific oyster, Crassostrea gigas, as a biological filter for a marine fish aquaculture pond. Aquaculture 92: 187-197.] Shpigel et al., 1993a, Shpigel M, Neori A, Popper DM and Gordin H. 1993a. A proposed model for ‘‘environmentally clean’’ landbased culture of fish, bivalves and seaweeds. Aquaculture 117: 115-128.] 1993b; Shpigel M, Lee J, Soohoo B, Fridman R and Gordin H. 1993b. The use of effluent water from fish ponds as a food source for the pacific oyster Crassostrea gigas Tunberg. Aquaculture & Fisheries Management 24: 529-543.] Neori and Shpigel, 1999; Neori A and Shpigel M. 1999. Algae treat effluents and feed invertebrates in sustainable integrated mariculture. World Aquaculture 30: 46-49, 51.] Neori et al., 2001 Neori A, Shpigel M and Scharfstein B. 2001. Land-based low-pollution integrated mariculture of fish, seaweed and herbivores: principles of development, design, operation and economics. European Aquaculture Society Special Publication 29: 190-191.] ). This technology formed the basis for a small farm (PGP Ltd.) in southern Israel.

IMTA as a method of sustainability

IMTA promotes economic and environmental sustainability by converting solid and soluble nutrients from fed organisms and their feed (e.g. intensive fish and shrimp farming) into harvestable crops (extractive organisms), thereby reducing the potential for eutrophication, and increasing economic diversification. Tournay B. 2006. IMTA: template for production? Fish Farming International, Vol. 33, No. 5, May 2006, pg. 27.]

If properly selected and placed, co-cultured species will have accelerated growth from the uptake of extra nutrients provided by the fed culture species. Johnson E. 2004. Cleaning up the sea cages. In: Family Jewels. Saltscapes, Vol. 5, No. 3, May/June 2004, 44-48.] Lander T, Barrington K, Robinson S, MacDonald B and Martin J. 2004. Dynamics of the blue mussel as an extractive organism in an integrated multi-trophic aquaculture system. Bulletin of the Aquaculture Association of Canada. 104(3): 19-28.] Ridler N, Robinson B, Chopin T, Robinson S and Page F. 2006. Development of integrated multi-trophic aquaculture in the Bay of Fundy, Canada: a socio-economic case study. World Aquaculture 37(3): 43-48.] This increases the overall environmental assimilative capacity of a site thereby reducing the potential for negative environmental impacts.

IMTA enables farm operators to diversify, often without the need for new locations or sites. Initial capital budgeting research suggests that recycling the waste of one crop as feed for another can increase profits in an IMTA system. Scenario analysis also indicate that IMTA can reduce financial risks due to weather, disease and market related risks. Ridler N, Wowchuk M, Robinson B, Barrington K, Chopin T, Robinson S, Page F, Reid G and Haya K. 2007. Integrated multi-trophic aquaculture (IMTA): a potential strategic choice for farmers. Aquaculture Economics & Management 11: 99-110.] Over a dozen studies have investigated the economics of IMTA systems since 1985.

Nutrient flow in IMTA

Typically, the fed culture species (i.e. upper trophic level) in an IMTA system have been carnivorous fish or shrimp, whose wastes augment the natural food supply or nutrient uptake of co-cultured extractive species. Fish and shrimp excrete soluble ammonia and phosphorus (orthophosphate), which are inorganic nutrients readily available to inorganic extractive species such as seaweeds. Fish and shrimp also release organic solids which can become food for shellfish and deposit feeders, Mazzola A and Sarà G. 2001. The effect of fish farming organic waste on food availability for bivalve molluscs (Gaeta Gulf, Central Tyrrhenian, MED): stable carbon isotopic analysis. Aquaculture 192: 361-379.] the organic extractive species.

Not all supplemental nutrients flow directly from the waste by-products of the fed species. For example, some ammonia may be generated by organic extractive species (e.g. shellfish) and also extracted by seaweeds. Waste feed may also be a source of additional nutrients; either directly available for consumption by organic extractive species (e.g. deposit feeders) or from the release of soluble nutrients by decomposition, for inorganic extractive species.

Nutrient recovery efficiency

Nutrient recovery efficiency in an IMTA system is a function of several factors. Culture system, harvest schedule, management, spatial configuration/proximity, production, selection of fed and extractive species, biomass ratio of species involved, availability of natural food sources, particle size, digestibility, season, light, temperature, and water volumes (flushing rate) all have the potential to influence growth rates and nutrient recovery efficiency. Since these factors will vary significantly between sites, systems and regions, a general percentage of IMTA nutrient recovery can not be simply reported. A site-by-site determination must be made.

Some of the first attempts to quantify nutrient recovery of an IMTA farm were reported by Neori et al. (2004). Shpigel et al. (1993b) presented the first quantitative performance assessment of a hypothetical family scale fish/microalga /bivalve/seaweed farm, based on actual pilot scale culture data. They showed that at least 60% of the nutrient input to the farm could reach commercial products, nearly three times more than in modern fish net pen farms. Expected average annual yields of the system (recalculated for a hypothetical 1 ha farm) were 35 tons of seabream, 100 tons of bivalves and 125 tons of seaweeds. This would, of course, be a technically demanding farm, requiring experienced hands to control changes in water quality and in suitability for bivalve nutrition, due to the inherently unstable phytoplanton populations. Krom MD, Porter C and Gordin H. 1985. Causes of fish mortalities in the semi-intensively operated seawater ponds in Eilat, Israel. Aquaculture 49: 159-177.]

Troell et al. (2003) reviewed 28 studies that reported dissolved nitrogen uptake efficiency of seaweeds in IMTA systems. Reported values ranged from 2 to 100% for 23 land-based studies. None of the 5 reviewed open-water studies reported nutrient recovery values. It is difficult to determine nutrient recovery in an open-water IMTA site due to the inherent "leaky nature" of the system. However, such information is necessary for ecosystem and integrated coastal zone management, and research on this aspect is ongoing. Reid GK, Robinson S, Chopin T, Lander T, MacDonald B, Haya K, Burridge F, Page F, Ridler N, Justason A, Sewuster J, Powell F and Marvin R. An interdisciplinary approach to the development of integrated multi-trophic aquaculture (IMTA): bioenergetics as a means to quantify the effectiveness of IMTA systems and ecosystem response. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 761. (]

Food safety and quality

A possible concern with the wastes of one species being the nutritional inputs for another is the potential for contaminants. To date, this does not appear to be a problem for IMTA systems. Mussels and kelps growing adjacent to Atlantic salmon cages in the Bay of Fundy, Canada, have been examined since 2001 for evidence of contamination by therapeutants, heavy metals, arsenic, PCBs and pesticides. Concentrations have always been either non-detectable or well below the regulatory limits established by the Canadian Food Inspection Agency, the USA Food and Drug Administration and the European Community Directives. Haya K, Sephton D, Martin J and Chopin T. 2004. Monitoring of therapeutants and phycotoxins in kelps and mussels co-cultured with Atlantic salmon in an integrated multi-trophic aquaculture system. Bulletin of the Aquaculture Association of Canada. 104(3): 29-34.] Chopin T, Sawhney M, Shea R, Belyea E, Bastarache S, Armstrong W, Reid GK, Robinson SMC, MacDonald B, Haya K, Burridge L, Page F, Ridler N, Justason A, Sewuster J, Powell F and Marvin R. 2007. An interdisciplinary approach to the development of integrated multi-trophic aquaculture (IMTA): the inorganic extractive component. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 177. (]

Some taste testing of IMTA products has also been conducted. These tests have indicated that mussels grown adjacent to Atlantic salmon cages have been free of "fishy" taint and could not be distinguished from wild mussels by the testers. Their meat yield is, however, significantly higher, reflecting the increase in food availability and energy.

elected IMTA projects

Several IMTA research projects have been ongoing over the last few years. These are described below.


Variants of IMTA in Japan, China, South Korea, Thailand, Vietnam, Indonesia, etc. have occurred for centuries in marine, brackish and freshwater. Fish, shellfish and seaweeds have been placed next to each other in bays, lagoons and ponds. Through trial and error, optimal integration has been achieved over time. However, while seemly quite common, there is no readily available data on the proportion of Asian aquaculture production that occurs in IMTA systems.


Bay of Fundy IMTA project

The Bay of Fundy IMTA project is a collaborative project with industry, academia and government and is presently expanding production to commercial scale. The current system includes Atlantic salmon, blue mussels and kelps; deposit feeders are being investigated. Phase one of the project was funded by AquaNet (one of Canada’s Networks of Centres of Excellence) and phase two is presently funded by the Atlantic Canada Opportunities Agency. 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). See Chopin et al. (2004, 2007) and Robinson et al. (2007) Robinson SMC, Lander T, Martin JD, Bennett A, Barrington K, Reid GK, Blair T, Chopin T, MacDonald B, Haya K, Burridge L, Page F, Ridler N, Justason N, Sewuster J, Powell F and Marvin R. 2007. An interdisciplinary approach to the development of integrated multi-trophic aquaculture (IMTA): the organic extractive component. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg.786. (] for additional details.

Pacific SEA-lab research initiative

Pacific SEA-lab is licensed for the co-culture of sablefish, scallops, oysters, blue mussels, urchins and kelps ("SEA" stands for Sustainable Ecological Aquaculture). The project presently aims to balance four species in an intensive IMTA design. The project is headed by Stephen Cross under a British Columbia Innovation Award at the University of Victoria [Coastal Aquaculture Research & Training (CART) network] . See Cross (2007) Cross S. 2007. Making the case: quantifying the benefits of integrated multi-trophic aquaculture (IMTA). World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 209. (] for further details.


Science and technology towards the reduction of environmental impact of intensive salmon culture is carried out at the Universidad de Los Lagos, in Puerto Montt, at the [ i-mar Research Center] . Initial research included integrated land-based aquaculture development with trout, oysters and seaweeds. Present research is focusing on IMTA in open waters with salmon, seaweeds and abalone. The project leader is Alejandro Buschmann. See Buschmann et al. (2007) Buschmann AH, Varela DA, Hernández-González MC, Henríquez L, Correa J, Flores R and Gutierrez A. 2007. The development of an integrated multi-trophic activity in Chile: the importance of seaweeds. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 136. (] for further details.


eaOr Marine Enterprises Ltd.

SeaOr Marine Enterprises Ltd., which operated for several years on the Israeli Mediterranean coast, 35 km north of Tel Aviv, was a modern intensive, land-based integrated mariculture farm. The farm cultured marine fish (gilthead seabream), seaweeds (Ulva and Gracilaria) and Japanese abalone. This farm best utilized the local advantages in climate, and recycled the fish-excreted nutrients into seaweed biomass, which was fed on site to the abalone. The process of nutrient recapture in the mariculture system was at the same time also an effective water purification process that allowed the water to be recycled to the fishponds or to meet point-source effluent environmental regulations.

PGP Ltd.

PGP Ltd. (1994) is a small IMTA farm in Southern Israel. It cultures marine fish, microalgae, bivalves and Artemia. Effluents from fed pond aquaculture of seabream and seabass are collect in sedimentation ponds, where dense populations of microalgae – mostly diatoms – develop. Clams, oysters and some times also Artemia filter the microalgae from the water, producing a totally clear effluent. The farm sells the fish, bivalves and Artemia.

outh Africa

Three farms currently grow seaweeds for feed in abalone effluents in land-based tanks. Up to 50% of re-circulated water passes through the seaweed tanks. Bolton J, Robertson-Andersson DM, Troell M, and Halling C. 2006. Integrated system incorporates seaweeds in South African abalone culture. Global Aquaculture Advocate, Vol. 9, No. 4, July/August 2006, pg. 54-55.] This is a somewhat unique IMTA system, as fish or shrimp do not comprise the upper trophic species. In this case, the driver is not nutrient abatement in the effluents, but avoiding overfishing of natural seaweed beds and avoidance of periods with red tides by turning the system in the recirculation mode. This commercially successful system was produced in research collaboration between the abalone farms (Irvine and Johnson Cape Abalone) and scientists from the University of Cape Town and the University of Stockholm.

United Kingdom

The Scottish Association for Marine Science, in Oban, is working on the development of IMTA systems by co-culturing salmon, oysters, sea urchins, and brown and red seaweeds under different projects ( [ MERMAIDS] , [ AAAG] , [ REDWEEDS] , [ SPIINES2] ). Research focuses on biological and physical processes, as well as production economics and implications for integrated coastal zone management. Researchers include: M. Kelly, A. Rodger, L. Cook, S. Dworjanyn, and C. Sanderson. See Kelly et al. (2007) Kelly MS, Sanderson C, Cook EJ, Rodger A and Dworjanyn SA. 2007. Integration: enhancing sustainability in open water aquaculture systems. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 458. (] and Rodger et al. (2007) Rodger A, Cromey C and Kelly M. 2007. Open water integrated aquaculture - use of depositional modelling to assist finfish/bivalve integration, for growth optimisation and prediction of waste dispersal. World Aquaculture Society. Aquaculture 2007 conference proceedings, pg. 788. (] for further details.

Other IMTA projects

Several other IMTA projects from the last three decades are reviewed by Troell et al. (2003) and Neori et al. (2004).

See also

*Extensive farming
*Factory farming
*Genetically modified organism
*History of agriculture
*Industrial agriculture
*Industrial agriculture (animals)
*Industrial agriculture (crops)
*Intensive farming
*Organic farming
*Sustainable agriculture
*Zero waste agriculture

References and notes

Neori A, Troell M, Chopin T, Yarish C, Critchley A and Buschmann AH. 2007. The need for a balanced ecosystem approach to blue revolution aquaculture. Environment 49(3): 36-43.

External links

* [ AquaNet IMTA]
* []
* [ World Aquaculture Conference 2007: IMTA session]
* [ Chopin lab]
* [|toc The Comparative Roles of Suspension-Feeders in Ecosystems] The use of bivalves as biofilters and valuable product in land based aquaculture systems - review.
* [ Seaweed Resources of the World] Algae: key for sustainable mariculture.
* [|toc Ecological and Genetic Implications of Aquaculture Activities] Evaluation of macroalgae, microalgae, and bivalves as biofilters in sustainable land-based mariculture systems.

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