Integrated Multi-Trophic Aquaculture

Sand worms

Integrated Multi-Trophic Aquaculture

Integrated Multi-Trophic Aquaculture (IMTA) uses the waste stream from producing one species as nutrients for other species. Farmers can combine fed aquaculture (e.g., fish, shrimp) with inorganic extractive (e.g., seaweed) and organic extractive (e.g., shellfish) aquaculture to create balanced systems for environmental remediation (bio-mitigation), economic performance (improved output, lower cost, product diversification and risk reduction) and social acceptability (better management practices and sustainability).

Selecting appropriate species and sizing the various populations to provide necessary ecosystem functions allows the biological and chemical processes involved to achieve a stable balance, mutually benefiting the organisms 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 (Wikipedia). IMTA in the ocean (offshore cultivation) can be done by the use of buoys with lines on which seaweed and/or shellfish grow. The buoys/lines are placed next to fish nets or cages. This method is already used commercially in Norway, Scotland, and Ireland.

IMTA can also be land-based, using ponds or tanks, or even open-water freshwater systems. Implementations have included species combinations such as shellfish/shrimp, fish/seaweed/shellfish, fish/seaweed, fish/shrimp and seaweed/shrimp (Wikipedia).

AHI's approach to IMTA

In 2014, AHI proposed to the National Science Foundation (NSF) a research and development plan whereby IMTA concepts could be paired to an RAS fish production system. Marine invertebrates and algae could be utilized to process excess fish feed, along with liquid and solid fish wastes, in a manner that would yield several valuable by-products. Rather than using traditional waste treatment systems such as drum filters, the waste stream from the fish tanks moves through a series of adjacent tanks containing sand worms, various micro-algae, oysters and macroalgae. This waste stream, containing fecal & feed waste, urine and CO2 is gradually processed by the various species, each using the nutrients it needs for growth. In this manner, all or most of the wastes are broken down and the water is cleaned and oxygenated before returning to the fish tanks. The design and operation of the system, along with identity of the various algae species used in AHI’s system are proprietary.

AHI’s IMTA pilot plant

In earlier small scale trials at the University of Maine’s Center for Cooperative Aquaculture Research (CCAR), AHI has demonstrated that its version of IMTA is feasible. The trials were done using both black sea bass (Centropristis striata) and California yellowtail (Seriola lalandi). Under a Phase II SBIR grant from NSF, AHI is now installing a larger scale system to advance its studies of IMTA. While operating at 5 times the volume of the earlier trials, AHI is studying additional species in the system, while developing a control system that would allow the technology to be used in a commercial production environment. The company will also study the economics of the system to determine the merits of commercializing some or all of the system in the future. As part of the project, the company will be harvesting and test marketing fish, sand worms and oysters to validate the company’s earlier market research.

Variations of Basic IMTA

Depending upon the scientific and economic results of the Phase II SBIR project, AHI hopes to commercialize some or all of its IMTA system. By making adjustments to the system and the manufacturing process, AHI believes it may be possible to run a version of the IMTA system even if certain components or species are not suitable for large volume production. Variations might include adding or deleting one or more species, or designing system modifications to delete individual processing steps. The company will evaluate all the costs for treating fish wastes, including capital equipment, labor and utilities, while comparing those costs to the added value of selling both fish and by-products. We are convinced that the ecological principles of IMTA are sound, in that we are mimicking what takes place in the wonderfully diverse environment of the ocean. Our studies to date indicate that a mix of species and a variety of trophic levels will confer health and stability on our system. To date, modern aquaculture has largely followed the monoculture agribusiness model. AHI hopes to demonstrate that there is an alternative, one that improves the economics of producing seafood, in harmony with the environment around us.