Monday, September 12, 2011

Everything by the book, but books were wrong

High-rise tank is new solution in farming fish,
by Arthur Max, Associated Press, from Seattle PI

KAMPERLAND, Netherlands (AP) — Adri Bout trawled Dutch waters for 25 years until he recognized the ocean's limits. Now he raises 100 tons of turbot a year in a unique high-rise tank that has overcome some of farmed fishing's most persistent problems.

"I knew 20 years ago there is an end. When you keep fishing like this, the North Sea will be empty," he says.

When he started out, Bout knew nothing about aquaculture.

Turning to neighbors and books for advice, he ran into headaches that plague enclosed farms like his: The fish suffered disease epidemics, he spent a fortune on energy to pump and heat water in his tanks, and he had to dispose of the fish waste without befouling the surrounding area.

"We did everything by the book. But the books were wrong," he said.

...Three years ago he took his turbot out of the standard meter-deep (three-feet) square concrete tank and put them in his experimental eight-tiered system. Each tier is a U-shaped fiberglass "raceway" 64 meters (210 feet) long with 15 centimeters (6 inches) of water and a swift current that sweeps away excrement and uneaten food pellets.

Bout uses gravity to circulate the water eight times an hour — traditional farms change water once hourly — running it through cleansing filters each time it drops to the level below. He says his electricity costs are one-quarter of a similarly sized farm that uses standard tanks.

He also doesn't let organic waste go to waste. While other farms flush water back into the sea laden with untreated feces, he oxidizes it for plant fertilizer or food for shellfish.

He discovered that disease-spreading bacteria thrive in water above 16.5 Centigrade (61.7 Fahrenheit), a temperature turbot can tolerate but is too cold for other ocean fish like bass or bream, which he once raised but abandoned. The fish grow more slowly in cool water but are free of disease, and Bout says he has not used medication for eight years. He also found that with cleaner the water the fish ate less, but grew faster.

...His next project is raising sole, finding a profitable formula. "You can think about sustainability. But you have to make money," he says.


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