A solid and scaly fish story

A solid and scaly fish story

I was born in Minnesota and grew up an avid fisherman and walleye (Sander Vitreus) was always my catch of choice. A firm and flaky walleye fillet made a fantastic meal, whether it was freshly caught in the lakes of northern Minnesota or at a nearby restaurant in the Twin Cities.

Walleye isn’t the only flaky and delicious fish on the menu these days. yellow perch (Perca flavescens) is a tasty and popular option and due to high demand and low supply these fish are currently fetching up to $38 a pound!

Yellow Perch. Credit: Robert Colletta/USDDepartment of Agriculture, Agricultural Research Service.

That was not always so. During the early to mid 20th century, large quantities of wild yellow perch were harvested throughout the Great Lakes region by both recreational and commercial fishermen. Over the past 50 years, overfishing and low recruitment (meaning a fish survives to market size) have drastically reduced wild yellowfish populations and harvest. In 2022 yellow perch support a much smaller commercial fishery and have evolved into a viable food fish species for aquaculture, which may involve breeding, rearing, and then harvesting fish, shellfish, and aquatic plants. Basically, it’s water farming. The development of aquaculture techniques to safely, efficiently and locally raise yellowfish by producers and researchers and organizations such as Sea Grant is underway.

I am part of a University of Minnesota Sea Grant (MNSG) project team raising yellowfish to compare methods and production costs between two common fish farming systems: recirculating aquaculture (RAS) systems and flow-through systems.

Person feeding Yellow Barch (fish) larvae in a tank.
Minnesota Sea Grant Aquaculture Extension employee Kieran Smith feeds yellowfish larvae in a tank. Credit: Amy Wardrobe/MNSG.

Historically, most yellowfish producers used large open-air ponds or flow-through systems that required large amounts of water, were difficult to clean, and difficult to remove fish waste. With the development of indoor RAS, water can be purified and reused with the help of certain types of bacteria (nitrifying bacteria). These bacteria convert the harmful waste products (ie, ammonia and nitrite) naturally produced by the fish into a less toxic form of nitrogen (ie, nitrate). RAS also helps isolate the fish from changing environmental conditions such as too hot or too cold water temperatures or predators and can reduce disease outbreaks.

In 2021, MNSG partnered with a local aquaculture expert, Chad Hebert, to help fine-tune our yellowfish aquaculture methods and help develop a user guide for aquaculture producers. We established a RAS at the Minnesota Aquatic Invasive Species Center Containment Lab on the St. Paul campus of the University of Minnesota. In Spring 2022 we successfully incubated and hatched our second batch of thousands of yellowfish eggs and grew them from fish larvae to juveniles measuring just under two inches long in mid-July. Growing her to this size took a lot of effort and dedication.

Yellowfish embryos and larvae under the microscope.
Photographs of yellowfish (Perca flavescens) embryos (A & B) and larvae (C) under the microscope. Perch eggs are spawned in a gelatinous matrix known as a “tape” or “tangle” that adheres to aquatic vegetation and/or substrate and is believed to reduce predation by other fish. Photo (C) shows a perch larva 10 days after hatching. The air pocket in the center of the fish is called the swim bladder, which provides buoyancy in the water. Just below the swim bladder is the digestive tract, or intestines, full of rotifers and brine shrimp. Photo credit: Kieran Smith

In the wild, newly hatched yellowfish larvae feed on a variety of microscopic aquatic animals known as zooplankton. In our RAS we offer our yellow perch larvae as live food such as rotifers and the like Artemia (i.e. brine shrimp), similar to what they would find in the wild, until they are large enough to eat kibble in pellet form. The MNSG project team not only breeds fish, but also different types of live food, each with its own challenges.

Plastic container of pellet sized fish food
As adults, our yellowfish eat pelleted fish food (Otohime brand EP2 fish food; 2.3mm pellets) purchased from Reed Mariculture. Credit: M. Thoms/MNSG.

Our Yellow Bass will not reach a crop size of 6-8 inches for 8-10 months.

When the project is completed by the end of 2023, the project team will produce a detailed handbook on rearing yellow perch in a RAS for fish producers. Our goal is to develop methods and cost estimates that are accessible for small to medium-sized producers to hatch, feed and raise yellowfish in a RAS to juvenile and market size. If we are successful, the handbook will provide information producers can use to increase local production of fresh, delicious yellowfish. Local fish production can also help address food insecurity issues across the Great Lakes region.

MNSG’s Yellow Perch Project is funded by, and is one of, a $134,879 grant from the National Sea Grant Office 13 nationwide projects developed to address the ongoing and long-term impacts related to the COVID-19 pandemic on seafood resources, including aquaculture and the link between aquaculture and wild caught fisheries.

For more information or to speak to a member of the project team, please contact Amy Wardrobe, MNSG Fisheries and Aquaculture Instructor, Don Schreiner, MNSG Interim Training Program Manager, or Kieran Smith, MNSG Aquaculture Training Staff .

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