Cleaning Up the System

November 1, 2010
By Mandy Calkins

As demand for seafood grows, so does concern about the impact of fish farms on the marine environment. One
aquaculture practice tries to soften this impact by turning farm waste into more profit.


It’s called integrated multi-trophic aquaculture, or IMTA. The system starts with fish or shrimp and integrates
them, or farms them alongside, other marine species such as kelp or filter-feeding shellfish. The “multitrophic” part of IMTA means the organisms involved are from different trophic levels, or places on the food chain of the marine ecosystem.

In one example of IMTA, researchers in New Brunswick grew blue mussels and kelp near existing salmon pens. Organic matter in the water column, such as uneaten food pellets from the fish cages, provided nutrients for the filter-feeding mussels. The kelp took up inorganic matter, such as nitrogen, from the fish waste.

Instead of leaving fish waste to accumulate in surrounding waters, where it could upset the ecosystem, an IMTA system uses the waste as nourishment for other species. And the shellfish and kelp do more than just clean up - they, too, can be harvested and sold, netting more profit for the farmer.

Future IMTA projects could add bottom-dwelling species to the mix to consume waste that settles on the sea
floor, keeping things even cleaner. Sea cucumbers or urchins, which are marketable as food, could fill this role. Researchers are still tinkering with variables in the IMTA system - and hoping the practice catches on with farmers as well as with environmentally minded seafood consumers.