IMTRAS: Exploring the potential of integrated multitrophic recirculating aquaculture systems

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By Milthon Lujan

Salmon smolt RAS. Courtesy: Nofima
Salmon smolt RAS. Courtesy: Nofima

The global demand for seafood products is increasing, putting pressure on traditional fishing practices and highlighting the need for sustainable aquaculture solutions.

Traditional aquaculture practices, especially those relying on open-flow systems, can raise concerns about water usage, waste management, and environmental impact. To address these challenges, innovative approaches such as Recirculating Aquaculture Systems (RAS) and Integrated Multi-Trophic Aquaculture (IMTA) are gaining ground.

In this regard, a team of scientists from the Hubbs-SeaWorld Research Institute and AquaFarm established a modular Integrated Multi-Trophic Recirculating Aquaculture System (IMTRAS) on land for fish, sea cucumbers, mussels, and macroalgae to optimize resource utilization while reducing water requirements and nutrient discharge levels.

The system comprised interconnected units housing California yellowtail Seriola dorsalis (fed fish), sea lettuce Ulva lactuca (biofilter), Mediterranean mussels Mytilus galloprovincialis (filter feeders), and warty sea cucumbers Apostichopus parvimensis (detritivores).

What are RAS and IMTA?

  • RAS: These systems reuse treated water, minimizing water consumption and offering better control over water quality and disease prevention. However, waste management within these closed systems remains crucial.
  • IMTA: This approach combines the cultivation of different species from various trophic levels (feeding levels) in a single system. This creates a mini-ecosystem where the waste from one species becomes food or resources for another, promoting sustainability and efficiency. For example, filter feeders like mussels can consume the waste produced by fish, creating a more balanced and sustainable ecosystem.
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Combining strengths: IMTRAS

Integrated Multi-Trophic Recirculating Aquaculture Systems (IMTRAS) take the concept a step further by merging RAS principles with IMTA within a closed loop. According to researchers, this innovative approach offers several advantages:

  • Reduced water consumption: By reusing treated water, IMTRAS minimizes freshwater usage compared to traditional open-flow systems.
  • Improved water quality: By incorporating waste-extracting species such as seaweeds and filter feeders, IMTRAS helps maintain water quality by removing excess nutrients and organic matter.
  • Better waste management: The integration of diverse species allows for natural biofiltration, reducing waste accumulation and improving water quality.
  • Diversified production: IMTRAS can produce multiple marketable seafood products, including fish, shellfish, and algae.
  • Greater efficiency: IMTRAS optimizes resource utilization by creating a closed-loop system with minimal waste and an efficient nutrient cycle.

Modular design for optimal efficiency

According to the study, IMTRAS employed a modular design, allowing for efficient management of different species and waste streams. The system consisted of two interconnected modules:

  • Module 1: Housing California yellowtail (fed species) and seaweeds (Ulva lactuca) acting as biofilters.
  • Module 2: Housing waste-extracting species: Mediterranean mussels (Mytilus galloprovincialis) and warty sea cucumbers (Apostichopus parvimensis).

Exploring IMTRAS potential

While research on IMTRAS is still in its early stages, initial studies have shown promising results:

  • Fish growth: California yellowtail (Seriola dorsalis) exhibited impressive growth rates in both trials, with improved feed conversion efficiency at higher population densities.
  • Sea lettuce performance: The macroalgae, Ulva lactuca, thrived, demonstrating high productivity and efficient nutrient absorption, particularly nitrogen. This highlights its efficacy as a biofilter, removing excess nutrients that could otherwise harm the system. Interestingly, the protein content of the algae also showed variation, suggesting potential for further exploration of its use as a food source.
  • Waste management: Mussels and sea cucumbers successfully removed a significant portion of the solid waste produced by the yellowtail, demonstrating their role in waste conversion and ecosystem balance within the IMTRAS.
  • Nitrogen balance: Nitrogen analysis within the system revealed a promising distribution. A substantial portion was converted into fish biomass and algae production, while the rest remained within the system for further utilization. This minimizes potential environmental impact due to excessive nitrogen discharge.
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Looking to the future

The study identified a possible co-cultivation ratio for this specific IMTRAS configuration. This valuable information paves the way for future improvements that maximize efficiency and productivity.

Further research is needed to optimize the design, operation, and species selection of IMTRAS for different production goals. However, initial findings suggest that IMTRAS holds great promise for the future of sustainable and efficient fishery production.


This study provides solid evidence of the viability of IMTRAS as a sustainable and efficient aquaculture solution. The modular design, impressive growth rates, efficient waste management, and positive nitrogen balance demonstrate the system’s potential to revolutionize fish and shellfish production.

As research continues, IMTRAS could become a key player in meeting the growing demand for seafood products while safeguarding our precious water resources and minimizing environmental impact.

The study was funded by the Pacific States Marine Fisheries Commission (PSMFC) and The Builders Initiative and SeaWorld, San Diego.

Mark Drawbridge
Hubbs-SeaWorld Research Institute, 2595 Ingraham Street, San Diego, CA 92109, USA.
Email: mdrawbridge@hswri.org

Huo, Y., Stuart, K., Rotman, F., Ernst, D., & Drawbridge, M. (2024). The culture of fish, mussels, sea cucumbers and macroalgae in a modular integrated multi-tropic recirculating aquaculture system (IMTRAS): Performance and waste removal efficiencies. Aquaculture, 740720.