By: Aaron R. Conklin, Wisconsin Sea Grant

More than a thousand walleye are spread between six sets of circular tanks at the University of Wisconsin-Stevens Point (UWSP) Aquaponics Innovation Center in Montello, Wisconsin. They swim around in near-total darkness, their environment protected by several sets of pitch-black curtains.

“Walleye are sunset and nighttime feeders,” explained Chris Hartleb, UWSP professor of aquaculture and the caretaker of the walleye colony. “Providing the curtains allows them to feed 24 hours a day. Plus, they’re very skittish fish—it takes almost nothing to startle them.”

There is good reason to keep them calm. These fish are a key part of a two-year aquaculture research project funded by Wisconsin Sea Grant designed to compare the production of walleye, a native Wisconsin fish, and saugeye, a natural hybrid of walleye and sauger, in a recirculating aquaculture system and a closed aquaponics system.

Chris Hartleb and Greg Fischer, the Facility Operations Manager of UWSP’s Northern Aquaculture Demonstration Facility (NADF) near Bayfield, Wisconsin, spent the last year raising saugeye in tanks with low (30kg/m³), medium (60kg/m³ ) and high (90 kg/m³) densities at each facility.

“The saugeyes grew really well,” said Fischer. “We reached our target goal of growing a one-pound fish in less than a year at each of the three densities. We even had some fish grow up to two pounds in weight.”

Better still, Fischer’s NADF operation and systems experienced no significant issues with maintaining water quality, a common problem that can often derail an aquaculture operation. Fischer is now raising walleye in six specialized dual drain, cornell-style tanks connected to a more traditional recirculating aquaculture system with a fluidized sand biofilter. The water containing the fish waste is drained, filtered and oxygenated before being pumped backed into the tanks to provide nutrients to a wide variety of plants, including several types of lettuce and kale. Hartleb has even tried growing broccoli.

Hartleb explains that “aquaponics is about purifying the water to a non-toxic level. It’s a closed system, and you’re basically acting as Mother Nature. Any change you make shifts everything.”

Currently, nearly 90 percent of the aquaculture industry in the United States is focused on tilapia. While this makes sense from a commercial standpoint in that tilapia grows well in high-density tanks and tends to return a good price at market, it raises some concern from a biological standpoint since it is like putting all eggs in one basket.

“As a biologist, it’s scary,” said Hartleb. “What if a disease wipes out tilapia fry at nurseries?” In fact, there are only three nurseries in the United States that provide tilapia fingerlings to aquaculture/aquaponics operations, and two of them are in the Southwest, not far from Mexico, which experienced a major outbreak of the lethal Tilapia Lake Virus earlier this year.

Walleye offers its own economic advantage. One-pound fillets typically fetch anywhere from $14-16 a pound. Hartleb and Fischer’s research could be critical to expanding Wisconsin’s aquaculture industry, with walleye representing the potential cornerstone of a successful aquaponics operation.

“That is the question–economically, how does this fit in? “ Fischer asked. “That is the big puzzle. Can you do this at a commercial scale? At NADF, we have been investigating and working on walleyes and their hybrids for food fish use for almost 10 years now and this research is critical to move this species forward for sustainable U.S. aquaculture.”

So far, results from Hartleb and Fischer’s research projects are encouraging. Walleye in the low-density tanks grew the best, reaching as high as a pound and a half in weight. In the medium density tanks, 93 percent of the fish reached one pound. The high-density tank was slightly less successful, however, with only 30 percent of the fish reaching a pound in weight.

Given the dual purpose of an aquaponics operation, that is not necessarily bad news. “If you find the lowest density is best, why wouldn’t you then grow more plants?” Hartleb asked.

With another year to go on the project, a significant amount of data analysis is required and a few bottlenecks will need to be resolved before walleye and saugeye can truly go mainstream. The biggest challenge is the lack of a nursery provider. If a new startup wants to begin raising walleye and saugeye, they need fingerlings. Walleye fingerlings are typically grown for stocking in lakes, not fueling startups, and UWSP-NADF doesn’t yet produce enough saugeye fry to become a regional supplier.

“We need a private industry partner to step up to the plate on this aspect of providing biosecure, feed trained, intensively reared fingerlings to support the industry. We know how to do this successfully and can help with training and setup.” said Fischer.

That’s where the education and outreach piece of the project comes in.

“We have the know-how. We have the tools. We can teach anyone,” said Hartleb, and Fischer agrees.

“If we can resolve some of these questions and continue working with and educating interested fish farmers, I’m confident that walleye and hybrids will be the next big thing for Wisconsin aquaculture.”