Creature Feature: Blue suckers can warn us when something is wrong with the river

Seldom seen bottom-feeders only live where the water is deep and clean, like the St. Croix, and can alert scientists to pollution.




4 minute read

Blue sucker (Photo: Spencer Neuharth / USFWS)

Blue suckers (Catostomus elongatus) demand big and clean rivers, which means they are rare. They are listed as a species of special concern in Minnesota, and threatened in Wisconsin. The St. Croix River is about as healthy as a river around here gets, and it is home to these fish that get very little attention, unless you want to know if the river is clean.

Because blue suckers are very sensitive to too much sediment in the water, or increases in other pollution, scientists look to them like a canary in a coal mine for degradation. If blue suckers disappear, something might be wrong.

Sentinel species

A scientist with the Minnesota Pollution Control Agency recently shared some information about blue suckers on social media. Mike Koschak uses living things like fish, insects, and more to assess the health of lakes and rivers. He pointed out the blue sucker’s sensitivity to water contamination makes it important.

Of the 100 or so fish species found in the St. Croix River, 14 are suckers and their cousins, buffalo, and redhorse in the St. Croix. Some are abundant like the redhorse sucker, some uncommon, like the river redhorse — and like the blue sucker.

The fish was originally found far up the St. Croix, separated by the Taylors Falls dam since 1906, but none have been seen above the since 1979.

Fickle fish

While its range includes the entire Mississippi River and its tributaries, as more rivers have been affected by human activity, the St. Croix and other streams in Minnesota and Wisconsin have become a refuge.

“Wisconsin populations of blue sucker represent some of the largest remaining in the upper Mississippi River basin, and therefore merit careful management,” the Wisconsin DNR states. “This species is intolerant to turbidity and pollution, so sources of pollution discharge and soil runoff within its range should be monitored and minimized.”

The lower Wisconsin River, which enters the Mississippi near Prairie du Chien in southwestern Wisconsin, is another blue sucker hotspot. The video below features a Wisconsin DNR biologist talking about their attempts to learn more about the fish and its habitat needs:

General information

Courtesy Fishes of Minnesota. Photographs by Konrad P. Schmidt, Text by Nicole Paulson & Jay T. Hatch in cooperation with the Minnesota Department of Natural Resources’ MinnAqua Aquatic Program.

What’s In a Name?

Blue sucker: named for its deep blue color

Cycleptus (sigh-klep´-tuss) refers to its small, round mouth; coined by the namer
elongatus (eelong-got´-tuss) means “elongate” in Latin; based on its long body.

Where Do They Live?

The blue sucker is one of Minnesota’s rare fishes, known only to live in its large, southern rivers, including the lower portions of the Minnesota, St. Croix, and Mississippi rivers. They are commonly located in deeper fast moving channels of these rivers where the bottoms have lots of gravel or cobble. They are found living with the following fish: shorthead redhorse, common carp, shovel nose sturgeon, sauger and walleye.

Cool Fact: The blue sucker is the most rare sucker in the state, but recently has been found in increasing numbers.

How Big Do They Get? How Long Do They Live?

The blue sucker has not been carefully studied. We believe it commonly lives to 7 or 8 years old, but it can live for more than 10 years. Lengths of 500-600 mm (20-24 in) or more are common. These fish typically weigh 2-3 kg (4-6 lbs). The Minnesota state record for this fish is 6. 85 kg (14 lbs 3 oz) and was caught from the Mississippi River in Wabasha County.

What Do They Eat?

Blue suckers keep roughly the same diet during the juvenile and adult period of their life cycles. Adults just include larger food items. They eat mostly aquatic insect larvae but also include crustaceans, plant materials and algae.

What Eats Them?

Since these fish are rare there is little known about what predators they may have. Young suckers are probably eaten by walleye and smallmouth bass, as well as fish-eating birds when they swim into slower shallow waters.

How Do They Reproduce?

Once again since these fish are so rare, there is little known about them. The spawning season probably runs from early May to mid June in Minnesota when the water temperatures exceed 10 °C (50° F). Adults probably migrate upstream into the areas or moderately swift current and good gravel bottoms. Recently hatched larvae probably drift downstream to areas of slower water over sand or finer gravel. No sucker species is known to provide any kind of parental care after spawning.

Conservation and Management

Currently, blue suckers are considered rare in Minnesota and are listed as a species of Special Concern. Like many species of large rivers, their life cycle probably has been impacted by the construction of locks and dams and the interference with free flow of the river.


  1. Cycleptus elongatus Species Profile, Minnesota DNR
  2. Blue Sucker (Cycleptus elongatus), Wisconsin DNR
  3. Blue sucker, Cycleptus elongatus (Lesueur, 1817), Fishes of Minnesota


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Creature Feature: Blue suckers can warn us when something is wrong with the river