Is Integrated Multi-trophic Aquaculture (IMTA) the future? 


Recently the European Market Observatory for Fisheries and Aquaculture Products (EUMOFA) hosted a webinar concerning the environmental footprint of aquaculture and its future development. Having visited aquaculture farms in Norway, Russia and the Faroe Islands myself, I have always been very sceptical concerning its impact on animals and the environment. On the one hand, the animals are kept in rather small tanks where they are born and bred while being fed with fodder that contains antibiotics. At the same time, organic waste from aquaculture leads to deserted submarine landscapes, devoid of life and extremely high in nutrient build-ups.

Quite obviously, these post-apocalyptic impressions stem from half-knowledge and, while of course holding some truth, do not correspond to contemporary aquaculture farming anymore. In this post I therefore consider a concept called Integrated Multi-trophic Aquaculture (IMTA) and associated Recirculating Aquaculture Systems (RAS). While I’m no expert in this field, I find it nevertheless highly relevant for the interplay of conservation, livelihood and sustainable development.

What is IMTA?

As the name implies, integrated multi-trophic aquaculture describes a type of aquaculture, where all levels of the trophic system are farmed together. The idea is to recapture and convert feed, waste, nutrients and by-product from on trophic level into fertiliser, food and energy of other levels and to establish a synergistic interaction between the species that are farmed together. The goal is to create a balanced system in order to reach environmental sustainability (biomitigation), economic stability through product diversification and risk reduction as well as social acceptability through better management practices.

Essentially, the IMTA concept comprises three trophic levels, which are dependent on each other: 

TL1: plants, microalgae, phytoplankton and macroalgae, absorbers of light, nutrients and carbon
TL2: detritivores (organisms that eat dead plants or animals), filter-feeders, gastropods (snails and slugs), sea cucumbers and grazing fish
TL3: Carnivorous consumers, subdivided into four sub-levels, consisting of

  • TL3.1: small fish, crustaceans, sea stars
  • TL3.2: larger fish
  • TL3.3: squids
  • TL3.4: sharks, dolphins, albatrosses 
Reproduced and adapted from EUMOFA, 2020, p. 1.

The raison d’être of IMTA

The conceptual idea of IMTA appears logical, but stands in stark contrast to commonly applied aquacultural practices where either monoculture or at least polyculture have been practiced. That means that farms have traditionally focused on high-yield species, such as Atlantic salmon (Salmo salar) in Norway, in order to generate species-based income for the farmers. While the economic yield appears to be good, the environmental costs are significant: on the one hand, the waste products from the farms enter the surrounding ecosystems as persistent chemicals with impacts on other marine species. On the other hand, treatment of farmed salmon, for instance against sea lice, has been carried out without prior studies on the treatment’s impacts on other species due to the uncontrolled release of treated water into the sea (e.g. Sævik et al. 2021).

Given that monoculture is oftentimes prone to diseases – either on land or in the sea – new concepts have been developed in order to reduce the impacts from and on single-species aquaculture. One of these concepts is IMTA. As such, the way IMTA functions is not new and could already be found more than 2000 years ago in the Han Dynasty in China where rice and fish were farmed together. In order to combat nutrient overload, it was especially China which pushed the idea of IMTA throughout the 1980s and established the first multi-trophic farms – albeit not under the IMTA-moniker. The term itself was established by two Canadian researchers in 2004 and has become common parlance since then.

However, in the Western countries the entire ideas behind the concept have grown rather inertly: in Norway, throughout the 1980s until 2010, the interlinkages between waste removal and nitrogen uptake by kelp, omega-3 contents of mussels grown in close proximity to fish farms and overall waste removal from salmon farms was documented. Also in the United States and Canada the idea of IMTA became ever more prevalent in the early 2000s. Yet, only in the second decade of the 21st century, Western countries started to recognise the benefits of IMTA and began to invest in projects to develop the idea further (EUMOFA, 2020, pp. 2-3).

IMTA in Sanggou Bay, China

As mentioned above, the entire profitability of IMTA as well as its environmental benefits would not have been possible without its application in China. Especially the widespread use of IMTA in Sanggou Bay, Shandong Province, has been a prime example for the successful use of the IMTA concept. The bay is around 163 sqkm in size of which more than 100 sqkm haven been used for aquaculture since the late 1980s. Here, different areas are used for different species, as the map shows.

A high-resolution version of this map can be found here.

To make this even more understandable, Fang et al. (2016, p. 202) write:

“[A]balone feed on kelp, and the kelp takes up nutrients released from the abalone [reference omitted]. Co-culture of finfish, bivalves and kelp links organisms from different trophic levels so that the algae absorb nutrients released from finfish and bivalves, and bivalves feed on suspended fecal particles from the fish. Since kelp and Gracilaria lemaneiformis [Common red alga] are cultured from December to May and from June to November, respectively, nutrients are absorbed by the algae throughout the year.”

Several studies published in the journal Aquaculture Environment Interactions have shown that IMTA provides for important benefits for the marine ecosystem and that species support one another when farmed correctly. That means that the quality of the farmed species is significantly higher than those stemming from single-species farms. The amount of nutrients in the water along with the production and productivity of phytoplankton in Sanggou Bay shows that while aquaculture does have a major influence on nutrient cycles, these are not negative, but rather supportive of sustainable growth.

IMTA as a way forward?

The above allows for the conclusion that the concept is not only successful, but that it contributes to a much better reputation for aquaculture. After all, aquaculture has come under fire in recent years due to “(i) the presence of parasites in aquaculture fish, (ii) the use of antibiotics to promote growth and prevent diseases, (iii) the origin of the aquafeed supplied to the farmed fishes, (iv) the excessive release of nutrients to natural water bodies, (v) the accumulation of aquaculture wastes in the seabed, and (vi) the impacts of aquaculture on wild populations and on the introduction of non-indigenous species” (Correia et al. 2020). Through an IMTA approach, however, these issues can be tackled. Moreover, the economic benefits of IMTA cannot be neglected, even though research has primarily dealt the financial sides of IMTA instead of a broader socioeconomic assessment (Knowler, et al. 2020).  

This being said, it can be considered rather certain that in the future IMTA will play a more prominent role than it does at present. After all, aquaculture entrepreneurs could merge in order to generate greener and more resilient farms, thereby to ensure sustainable livelihoods and ultimately to produce products that are of high environmental and welfare quality. Given that IMTA is a concept that has not been explored in depth, more research is needed since the system applied in Sanggou Bay may not be the best for other regions where environmental, climatic and social conditions are different. However, in my view, in IMTA can play an important role in the sustainable utilisation of marine species, in environmental protection and in the generation of sustainable livelihoods. While currently still under-explored, governments could/should invest into this mode of aquaculture in order to reach their sustainable development goals.


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