A firm, flaky fish story

A firm, flaky fish story

I was born in Minnesota and was an avid fisherman in my youth and walleye (glazed sander) has always been my go-to catch. A firm, flaky walleye fillet made a fantastic meal, whether freshly caught from the lakes of northern Minnesota or at a restaurant closer to home in the Twin Cities.

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

Perch yellow. Image Credit: Robert Colletta/USD Department of Agriculture, Agricultural Research Service.

This was not always the case. During the early to mid-20th century, large numbers of wild yellow perch were harvested by recreational and commercial fishers throughout the Great Lakes region. Over the past 50 years, overfishing and poor recruitment (meaning a fish surviving to marketable size) have dramatically reduced wild yellow perch populations and harvest. By 2022 yellow perch supports a much smaller commercial fishery and has become a viable food fish species for aquaculture, which can include breeding, rearing, and then harvesting fish, crustaceans, and aquatic plants. Basically, it’s farming in the water. The development of aquaculture techniques to raise yellow perch safely, efficiently and locally by producers, researchers and organizations like Sea Grant is ongoing.

I am part of a project team at the University of Minnesota Sea Grant (MNSG) raising yellow perch to compare production methods and costs between two common fish farming systems: aquaculture systems in recirculation (RAS) and continuous flow systems.

Person feeding yellow perch (fish) larvae in a tank.
Minnesota Sea Grant Aquaculture Extension Associate Kieran Smith feeds yellow perch larvae in a tank. Image credit: Amy Schrank/MNSG.

Historically, most yellow perch producers used large outdoor ponds or circulating systems that required a lot of water, were difficult to clean, and difficult to remove fish waste from. With the development of indoor RAS, water can be cleaned and reused using specific types of bacteria (nitrifying bacteria). These bacteria convert harmful waste products (i.e. ammonia and nitrite) created naturally by fish into a less toxic form of nitrogen (i.e. nitrate). RAS also helps insulate fish from changing environmental conditions such as too hot or too cold water temperatures or predators and can reduce outbreaks.

In 2021, MNSG partnered with local aquaculture expert, Chad Hebert, to help refine our yellow perch aquaculture methods and contribute to the development of an Aquaculture Producers User Manual. We have set up a RAS at the Minnesota Aquatic Invasive Species Center Containment Lab on the St. Paul Campus of the University of Minnesota. In the spring of 2022, we successfully incubated and hatched our second batch of thousands of yellow perch eggs and grew them from larval fish to juvenile fish which, in mid-July, were just under two inches tall. long. Growing them to this size took a lot of effort and commitment.

Perch embryos and larvae under the microscope.
Photos of embryos (A & B) and larvae (C) of yellow perch (Perca flavescens) under microscopy. Perch eggs are laid in a gelatinous matrix known as a “ribbon” or “skein” which 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 bubble in the center of the fish is called a swim bladder, which provides buoyancy in the water. Just below the swim bladder is the digestive tract or intestine filled with rotifers and brine shrimp. Image credit: Kieran Smith

In the wild, newly hatched yellow perch larvae feed on a wide range of microscopic aquatic animals called zooplankton. In our RAS we offer our perch larval live foods such as rotifers and Artemia (i.e. brine shrimp), similar to what they would find in the wild, until they are large enough to eat dry pelleted food. The MNSG project team not only grows fish, but we also grow different types of live foods, each presenting their own challenges.

Plastic container with granulated fish food
As adults, our Yellow Perch eats pelleted fish food (Otohime brand EP2 fish food; 2.3mm pellets) purchased from Reed Mariculture. Image credit: M. Thoms/MNSG.

Our yellow perch will not reach a harvest size of 6-8 inches for 8-10 months.

When the project is completed at the end of 2023, the project team will produce a detailed manual on how to raise yellow perch in a RAS for fish producers. Our goal is to develop methods and cost estimates accessible to small and medium growers to hatch, nurture, and grow yellow perch to fry and market size in a RAS. If we are successful, the manual will offer information that growers can use to increase local production of fresh, delicious yellow perch. Local fish production can also help solve food insecurity issues throughout the Great Lakes region.

The MNSG Yellow Perch project is funded by a $134,879 grant from the National Sea Grant Office and is one of 13 national projects designed to address the ongoing and long-term impacts associated with the COVID-19 pandemic on seafood resources, including aquaculture and the link between aquaculture and wild fisheries.

For more information or to speak to a member of the project team, contact MNSG Fisheries and Aquaculture Extension Educator Amy Schrank, MNSG Acting Extension Program Manager Don Schreiner , or MNSG Aquaculture Extension Associate Kieran Smith.

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