Aquaculture already supplies approximately 50 percent of the fish and seafood consumed worldwide, and production is steadily increasing. Further development of the aquaculture industry in Canada could mean significant economic growth as well as job opportunities for Canadians – especially in coastal and rural areas. Responsible growth of the industry will depend on continued research to find innovative ways to improve the environmental performance and diversification of the sector.
- Integrated Multi-Trophic Aquaculture: A new approach
Integrated Multi-Trophic Aquaculture (IMTA) is one solution that encourages greater environmental stewardship while increasing economic benefits for growers and communities. IMTA is a different way of thinking about aquatic food production that is based on the concept of recycling. Instead of growing only one species (monoculture) and focusing primarily on the needs of that species, IMTA mimics a natural ecosystem by combining the farming of multiple, complementary species from different levels of the food chain. For example, one form of IMTA is to grow fish, invertebrates (like mussels and sea cucumbers) and seaweeds close together for the benefit of each crop and the environment.
- How it works
IMTA involves cultivating organisms in a way that allows the uneaten feed, wastes, nutrients and by-products of one species to be recaptured and converted into fertilizer, feed and energy for the growth of the other species. IMTA farmers combine species that need supplemental feed such as fish, with “extractive” species. Extractive species can include filter feeders (e.g., mussels) and deposit feeders (e.g., sea urchins), and seaweeds (e.g., kelps). The filter feeders and deposit feeders use the organic particulate nutrients (uneaten feed and faeces) for nourishment. The seaweeds extract the inorganic dissolved nutrients (such as nitrogen and phosphorus) that are produced by the other farmed species. Essentially, extractive species act as living filters. The natural ability of these species to recycle the nutrients (or wastes) that are present in and around fish farms can help growers improve the environmental performance of their aquaculture sites. In addition to their recycling abilities, the extractive species chosen for an IMTA site are also selected for their value as marketable products, providing extra economic benefits to farmers.
IMTA mimics a natural ecosystem by combining the farming of multiple, complementary species from different levels of the food chain.
- Designing an Effective IMTA System
An effective IMTA operation requires the selection, arrangement and placement of various components or species, so as to capture both particulate and dissolved waste materials generated by fish farms.
The selected species and system design should be engineered to optimize the recapture of waste products. As larger organic particles, such as uneaten feed and faeces, settle below the cage system, they are eaten by deposit feeders, like sea cucumbers and sea urchins. At the same time, the fine suspended particles are filtered out of the water column by filter-feeding animals like mussels, oysters and scallops.
The seaweeds are placed a little farther away from the site in the direction of water flow so they can remove some of the inorganic dissolved nutrients from the water, like nitrogen and phosphorus.
IMTA species should be economically viable as aquaculture products, and cultured at densities that optimize the uptake and use of waste material throughout the production cycle.