About one kilometer off the Kona coast of Hawaii, 80,000 yellow-tail, an alternative to wild-caught tuna, swim at ease in an enormous submerged aquaculture pen. Only a small buoy is visible from the black lava shoreline. Normally, parasites drifting in the ocean can attach to the containment mesh of aquaculture pens. There they multiply, and move onto the fish, causing immediate irritation and stress to the fish. If parasite levels are left unchecked, numerous parasites attach to each fish leading to bacterial infections and death. Until recently, the only way to remove the parasites was to bathe the fish in a dilute hydrogen peroxide solution. Now a fish farm in Hawaii is using a special copper-alloy mesh with a smooth surface that parasites cannot grip, resulting in a much healthier fish.
Neobenedenia, the parasite of concern in Hawaiian offshore fish farming, reproduces by releasing up to several hundred eggs daily. These eggs are composed of a rugged shell and a long tendril. The tendrils allow the eggs to attach directly to netting or to fouling on the netting. Bathing of contained fish in a chemical compound such as hydrogen peroxide only removes the parasite from the skin of the fish, leaving unhatched eggs attached to the netting unharmed. These eggs will hatch and can re-infect the fish within the net pen. Preventing reinfection requires a significant reduction in the ability of parasite eggs to efficiently colonize the netting material. This is what copper-alloy mesh accomplishes.
InnovaSea Systems was the first U.S. company to equip submersible open ocean fish pens with copper-alloy mesh. Each of their amazing SeaStations installed at Blue Ocean Mariculture (BOM) has a constant volume of 8,000 cubic meters. BOM decided to install three SeaStations following a study they performed in 2012. In nontechnical terms, results showed that copper-alloy mesh had about 1,000 times fewer parasite eggs per square meter than standard nylon mesh, leading to the conclusion that copper-alloy mesh pens should vastly reduce their problem. BOM President Todd Madsen noted, “The copper-alloy mesh seems to be working as advertised for us in Hawaii. The pens are clean and our treatment frequencies are down. The fish look great and are on or above their growth curve.”
Marine aquaculture nets and pens made with copper-alloy mesh are emerging as an effective solution to important problems facing the open ocean fish farming industry. Typical net pens constructed from synthetic materials with anti-fouling coatings become encrusted with marine organisms after only several months of use. Copper-alloy nets, however, remain free of fouling for years. This important benefit improves fish health, increases the rate of fish growth and eliminates the need to clean or replace pens. The mechanical strength and resilience of a copper-alloy structure also helps to prevent predator attacks and the escape of fish from aquaculture nets and pens.
The technology is also enabling the transition to open ocean aquaculture with reduced environmental impacts. According to a World Bank report, while the global harvest of wild-caught fish is declining, the expansion of aquaculture at roughly 8 percent per year for the past 30 years is expected to continue. Key to maintaining that growth in food supply is the ability to move aquaculture operations to off-shore high-energy environments that are unsuitable for typical near-shore fish-farming practices.
BOM’s Hawaiian Kampachi are raised in the deep, open ocean waters off the Kona coast. Consistent water temperature, strong ocean currents and a high capacity for renewal make these waters ideal for sustainable finfish mariculture.
Advanced copper-based technology is enabling innovation in the aquaculture industry. Innovators in Korea, Japan and Chile are applying copper-alloy mesh to expand the horizons of aquaculture into the open ocean and achieve a higher level of sustainability. Hal Stillman, Director of Technology Development and Transfer for the ICA sums it up: “The entire supply chain—copper-alloy producer, wire fabricator, mesh weaver, aquaculture pen company, fish farmer and environmental regulators–is collaborating to make aquaculture work better.”