US - Fish thrive in former sewage tanks

The sight of fish swimming in old sewage tanks might be disconcerting to some.

But one researcher hopes the paddlefish growing at Frankfort's wastewater treatment plant might one day lead to another source of food for consumers and income for limited resource farmers.

It's all a part of a combined effort from public and private entities "including Kentucky State University" to research a groundbreaking form of aquaculture using old and unused resources at the plant to grow paddlefish.

And it's working.

The process begins when tiny fingerling paddlefish are placed in large, old concrete tanks called digesters. The 300,000 gallon-digesters are no longer used to treat wastewater at the plant. Inside the tanks, the tiny paddlefish live in water disinfected with ozone.

For the first 30 days of the paddlefish's stay at the plant, they feed on daphnia, a food source that occurs at the plant during the treatment process of the sewage, said KSU professor Steven Mims.

As sludge settles to the bottom of a clarifying tank, daphnia is formed. Both Mims and Frankfort Sewer Director Bill Scalf said they don't know how or why the daphnia occur there.

A tiny crustacean that feeds on bacteria, daphnia agitates the sewage sludge, sometimes keeping part of it from settling, Scalf said.

But the treatment plant's problem has been turned into free food for the developing paddlefish, as researchers harvest the daphnia from the clarifying tank and transport it to the tiny paddlefish in the digesters, where for a month the fish feast on the food.

Harvesting the daphnia from the clarifying tanks has also made it easier for treatment plant employees to keep the wastewater clean, Mims said.

"They (the plant operators) don't want it and we do want it," Mims said.

After about a month, the fish reach three inches in length and outgrow the daphnia diet. But they are kept in the tank for about another three months, where Mims feeds them specially formulated pellets.

The water within the digester where the fish are grown is also important. It has been disinfected with ozone, Mims said, and is the same water that the plant releases into the Kentucky River on a daily basis.

In this water, the fish have thrived. Mims " in the second year of research at the plant " estimates a 90 percent survival rate for fish from the time they are put into the tank as fingerlings. That rate is quadrupled from the best batches he has raised at different locations, he said.

"The fish itself is an indicator that the water (at the plant) is good," Mims said.

From the time the fish are stocked into the concrete tank as fingerlings in May, the fish grow to 12-14 inches, so that by September, they can be released into Kentucky waters, Mims said. Last year, about 20,000 paddlefish were grown and this year Mims expects at least to double that.

Currently, the fish are tube-shaped, about the size of a human hand, with a tongue depressor-shaped bill protruding from the snout area. The fish are a blue-black color, which Mims said is darker than its normal gray because the tanks don't allow the fish to reach depths that keep them out of the sun.

While KSU is in charge of research, the fish are supplied by Aquila International and its president, Tim Parrott, who owns the fish and plans to sell them as a food product. Last year, he stocked several municipal reservoirs in the state with the fish and said he hopes for the fish to grow to 10 -15 pounds within three years, when they can be harvested and sold to restaurants.

Parrott and Mims concede the paddlefish is a new product on the market and may take some time to catch on with consumers. Mims likened paddlefish meat to that of swordfish "a lean white meat with a firm texture".

At a recent presentation Mims served several variations of the fish in a blind taste test to 13 chefs from high-end southeastern regional restaurants. He said all but one of them said they would serve it in their restaurants.
Mims said there are two options for stocking the fish in September. First, they can be put into a poly-culture setting, such as a catfish pond, where Mims said the fish would grow to 5 pounds within the first year.

Second, they can be placed in a large body of water for what he called reservoir ranching, which gives each of the filter-feeding fish between five and 10 acres to graze on zooplankton. In eight to 10 years, the fish could be harvested for not only their meat, but also their roe, or eggs, which are a form of caviar, Mims said.

The aquaculture program at KSU "one of the top programs of its kind in the nation" and City of Frankfort made an agreement to conduct the research at the plant. The deal called for KSU to pay $1,000 to offset utilities and miscellaneous costs, Scalf said.

Mims hopes the results of his research will push farmers and other municipalities with abandoned sewer tanks to invest in this aquaculture. He said several nearby sewage treatment plants have the needed equipment to grow the fish and said daphnia also occur at those plants.

He also said the national importation of fish versus the exportation of fish is the top trade deficit for the United States " another reason he hopes that this form of aquaculture can catch on.

One Web site listed the price of 14 ounces of North American caviar "that which is produced by paddlefish" at $312. Another site sells one ounce of paddlefish caviar for $36.

To Parrott, it all seems logical that people produce paddlefish.

"We need to spend more time growing fish in this country," he said.