A take on the IMTA system

Integrated multi-trophic aquaculture is an innovative and environmentally sound 'future farming' aquaculture solution to the growing demand for food. IMTA systems work by utilizing the waste from one aquatic species, like salmon at the higher trophic level to feed other species such as

mussels and seaweed. The use of multi-trophic aquaculture can reduce the impact of wild harvest fisheries but replicating natural systems. It can also limit the nutrients and organic matter outputs from aquaculture through bio mitigation. The species at the highest trophic level are the fed aquaculture which are typically carnivorous fish which excrete soluble ammonia and phosphorus, these nutrients are then consumed by extractive species such as seaweed or shellfish. Species that occupy the intermediate trophic level are also used for filtering organic bottom-level organisms and reducing pathogens such as sea lice. IMTA systems can be applied to fresh water, offshore or land based ecosystems. IMTA in open water cultivation if often done on salmon farms where the highest trophic level occupy, buoys with lines are used to facilitate seaweed growth and are often placed next to fishnets or cages where the bottom feeders are housed. In an IMTA model, the biological and chemical processes should balance. This can be achieved by the appropriate selection of different species and their proportions so they can develop into a stable ecosystem. In an ideal multi-trophic aquaculture the co-cultured species all contribute commercial value and the nutrient waste is minimised. There are many potential applications of IMTA in New Zealand such as the farming of Eel enhanced by the by-products from dairy and other agricultural/ horticultural waste. Offshore IMTA can also create additional habitat in the photic zone, yielding additional natural biomass. The future of multi-trophic aquaculture is bright as many nations such as Canada and Norway have shown positive results with their experimental trials.