Better water equals better fish. That’s the thinking behind a 24-meter diameter fish farming system developed by AgriMarine Holdings, a company based in Vancouver, British Columbia, that specializes in fish farming and developing sustainable aquaculture technologies. The company has proof that the idea works, with its 3,000-cubic-meter tank yielding significantly higher salmon output per volume than conventional fish farming environments, says AgriMarine CEO Sean Wilton.

The company’s approach depends upon using a material that is tough enough to withstand the pounding of waves and immersion in salt water. What’s needed is the right combination of fatigue and corrosion resistance, which led AgriMarine to a specific choice – composites. The AgriMarine System™ floating semi-closed containment tank is made from GFRP.

Wilton notes that salt water aquaculture, such as the raising of salmon, is traditionally done in a net enclosing a parcel of ocean. The water the fish swim in reflects whatever drifts in from the surrounding sea. Thus, the temperature and oxygen level fluctuate, as do the pathogen, parasite and contaminant loads. “You’re basically at the whims of nature,” says Wilton. “What is inside your net is identical to what is outside your net for the most part.”

The AgriMarine tank mitigates these issues by isolating fish from the surrounding water. The water that goes into the tank is pumped up from the depths of the sea, thereby enabling more control of the environment. The temperature of the water inside the tank can be optimized, as can the water’s oxygen concentration. Together, these factors enable fish to grow faster, cutting the time required to raise a crop, says Wilton. In addition, water-borne surface contaminants – natural or man-made – don’t reach the fish. Controlled and constant circulation of water provides optimal oxygen mixing and distribution. The fish swim at a planned speed, with the exercise producing highly desirable firm flesh.

Wilton notes that fish farming tanks have been considered before, but the idea was not pursued due to concerns about scale and cost. However, the ability to spread the expense over the lifetime of the tank changes that equation, with better feed efficiency and lower cost to treat parasites also improving the economics.

Pulling off this idea, though, requires a large tank with some special material properties. The enclosure has to float in the water and so is subject to wave action, which causes the structure to bend and flex. The tank also is exposed to corrosive salt water. AgriMarine investigated and tried various materials, including rubberized fabric, aluminum and floating concrete. However, these were too expensive, too weak, corroded too quickly or exhibited all of these failings.