How To Farm the Seas Without Waste

This is probably one of the only times fish sellers and environmental conservationists agree on something. A unique approach to fish farming called integrated multi-trophic aquaculture is gaining popularity within the modern industrial aquaculture industry, and the results are a little hazy.

Aquaculture research company Longline Environment defines integrated multi-trophic aquaculture, or IMTA, as systems that “combine fed aquaculture such as finfish or shrimp with extractive organic matter of shellfish and extractive inorganic aquaculture of seaweed.” In simple terms, IMTA involves reusing nutrients released by fish farms to support surrounding ecosystems.

Similar processes to IMTA have already taken root in parts of Asia and South America, but Canadian researcher Thierry Chopin hopes to develop an approach more aligned with North American aquaculture conditions.

Chopin, a marine biologist at the University of New Brunswick, has been working with Cooke Aquaculture to lower what’s considered water pollution caused by fish farming using IMTA. “We have to stop thinking of nutrients as wastes and pollution. Nutrients are needed in any ecosystem and they need to be reused more efficiently,” Chopin wrote in an email.

In an IMTA system, clusters of shellfish and macroalgae (seaweed) lie adjacent to fish farms and thrive on what would typically be water pollutants. Seaweed would absorb excess nitrogen and phosphorus from fish waste and shellfish would utilize the small organic particles in waste.

The research aims to address three points, Chopin said. The first, environmental sustainability, involves ecosystem services and green technologies for improved ecosystem health. Another is economic stability, comprised of improved output, lower costs, product diversification, risk reduction, and job creation. The last, societal acceptability, consists of better management practices, improved regulatory governance, and appreciation of safe projects.

The environmental efforts are noble but might stop short. Chopin predicted a decrease in water pollution anywhere from 10 percent and 50 percent but the exact outcome is hard to calculate. Still, “the environmental benefits are local, like within a few hundred feet of a fish farm,” said Dr. Ronald Hardy, the director of the Aquaculture Research Institute at the University of Idaho. There are also a limited number of places in North America where the system is feasible, in part because we don’t raise much salmon, and in part because getting approval for IMTA would be “impossible,” Hardy said.

The bigger impact may be economic, according to Hardy, who says wasted nutrients not retained by farmed fish are costing companies money. “It is metabolically impossible for nutrients to be 100 percent converted into fish tissue. For protein, fish retain under optimum conditions and with optimum diet formulations about 53 percent. The rest is metabolized and nitrogen is excreted as ammonia from unretained protein.” If other species are thriving off of the wasted nutrients, companies have more products to sell. Everyone wins.