Integrated Multi-Trophic Aquaculture (IMTA) is a type of aquaculture where several aquatic species from different trophic levels (eg. fish, seaweed, shellfish or other invertebrates) are farmed in close proximity in the same production system to improve efficiency, reduce waste and provide ecosystem services, such as bioremediation.
The ‘Strategic guidelines for a more sustainable and competitive EU aquaculture for the period 2021 to 2030’ promote IMTA, among other types of aquacultures that are most beneficial for the environment and the climate.
IMTA can cover many different types of aquaculture systems, such as land-based aquaculture systems (e.g. ponds) and net pens systems (e.g. combination of fish farming with off-bottom and on-bottom systems for bivalve molluscs and seaweed production). However, the aim is always to increase environmental sustainability, economic stability and social acceptability, within holistic and circular economy approaches.
IMTA systems enhance aquaculture sustainability by mimicking natural nutrient cycles. In these systems, the organic matter that is not used by one species, such as fish, becomes a resource for others, like seaweed and molluscs, which use the nutrients to grow. The effectiveness of the system depends on environmental factors, such as nutrient levels in the area, food availability and hydrodynamics.
Several challenges remain in the adoption of IMTA. For example, according with the EU legislation, aquaculture animals cannot be feed on waste, which means that the legal framework in force invalidate models where fish are combined with certain filter feeders and detritivores species (low trophic species as bivalve molluscs and sea cucumbers) which recycle the nutrients from fish uneaten feed and faeces. To assess and help address these challenges the EU is funding several projects on IMTA such as Astral (https://www.astral-project.eu/ ) and AquaVitae (https://aquavitaeproject.eu/).