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Canadian scientists have determined that an ancient Chinese way of farming fish is easier on the environment than commercial operations today and potentially more profitable. This ScienCentral video explains.
Ancient Chinese Secret
In aquaculture, it's dangerous to put all your salmon eggs in one basket. A fiercely cold winter, a nasty batch of parasitic sea lice, or a tenacious pathogen could turn your fish harvest belly up. But scientists working off Canada's misty east coast are proving that an ancient Chinese fish farming technique can reduce pollution generated by salmon farms and make money.
The research team, led by University of New Brunswick marine biologist Thierry Chopin, is one of many aquaculture projects around the world trying to find a more sustainable and less polluting way of farming fish. Normally commercial aquaculture is a single species production. Farmers raise fish, shellfish, or seaweed. If they raise fish, they can spend a good chunk of change running giant filtration systems to remove fish waste and uneaten food from their fish pens. These materials can load dangerous amounts of nutrients and organic matter into the water. But Chopin's team is working on an alternative. They are growing salmon, mussels, and seaweed together - an approach used by the Chinese for thousands of years, and formally called integrated aquaculture.
"All three together benefit," says Chopin. "The mussels and the seaweeds are taking advantage of the extra food available at the site to grow. So it's combining the three species to balance the system."
Image: AquaNet
At three experimental sites in the Bay of Fundy, Chopin and his colleagues surrounded salmon cages with wooden rafts. From the bottom of each raft long lines of mussels drop down into the depths of cold blue water. A few hundred meters off, giant yellow mooring buoys glow through the fog, connecting more lines, but these run just below the surface of the water and are draped in seaweed. In this integrated aquaculture system, salmon waste and bits of uneaten food dissolve into nutrients and organic matter – a perfect meal for mussels and seaweed growing nearby.
Chopin and his colleagues reported in the journal Aquaculture that mussels absorb the bits of organic material released from the fish pens, while the seaweeds combine the dissolved nutrients with solar energy to grow. Essentially the researchers are using waste materials from their fish pens to fertilize their mussels and seaweeds.
Chopin says the results are extraordinary. At the 2005 meeting of American Association for the Advancement of Science in Washington, D. C., Chopin reported that nutrient levels around the salmon pens could be reduced by as much as 60 percent as compared to typical commercial pens. He also said the mussels and the seaweed are growing twice as fast as those grown without salmon nearby. "So for example, for mussels we reach commercial scale in 18 months instead of 24 months," says Chopin.
Not only can the mussels and the seaweed be sold on Canada's multimillion dollar aquaculture market as seafood and ground fertilizers, but like conventional mechanical filtrations systems, they also provide a filtration service. Chopin says this service "should have an economic value on top of what you can sell them for as marine crops."
Underwater mussels sucking up bits of organic matter. Image: AquaNet
Feeding mussels and seaweed with salmon waste can improve water quality and help maintain a profitable and diversified fish farm, but scientists say it is unlikely to affect toxin levels found in the fish themselves. PCBs and heavy metals gather in farmed salmon as a result of their diet, not their environment.
"Most of the bioaccumulation is in the food chain, not absorbed through the water," says Jim Carlsberg, President of Kent SeaTech Corporation, an aquaculture company based in San Diego, California that grows mostly striped bass.
Considering the toxic reputation of farmed salmon, Chopin says his team has been monitoring tissues from their mussels and seaweeds to see if any of the chemicals from the fish are passing to the two other species. Based on the Canadian Food Inspection Agency's regulations, Chopin claims everything is below regulation levels.
Chopin hopes his team's research will soon allow commercial fish farmers to run integrated aquaculture systems in Canada. Though legal in the United States, currently large-scale versions of integrated aquaculture are prohibited under the Canadian Shellfish Sanitation Program. Language in the CSSP says,"Shellfish and finfish should not be raised in close proximity as net pens have the potential to be point-sources of pollution due to human activity and poor husbandry practices."
Underwater seaweed absorbing excess nutrients in the water. Image: AquaNet
"It's an old regulation and integrated aquaculture is paying the price for it," says Chopin.
Over the last eleven months, Chopin's team's research has helped change legislation in Canada on the local and regional level. Now they are working to overhaul the legislation on the national level.
Chopin says, "It's just a matter of finding a way to do the proper amendment."
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