What's In a Name?
Brook stickleback: refers to the spines on its back and the small streams where it lives

Culaea (kul-lay´-ah) a name created for this fish
inconstans (in-kon´-stans) means "variable" in Latin

Where Do They Live?
The brook stickleback is common throughout the state of Minnesota. It favors areas of rivers, streams, lakes, and ponds that have cool, unclouded (not turbid) waters with large amounts of vegetation. They often are found living with white suckers, creek chubs, fathead minnows, finescale dace, northern redbelly dace, and central mudminnows.

How Big Do They Get?
How Long Do They Live?
Brook sticklebacks are minnow-sized fish. They usually do not grow much bigger than 60 mm (2.4 in). The biggest ones reach about 80 mm (a little over 3 in). The brook stickleback is like many of the smaller species in Minnesota in that it lives for only 1 to 2 years, occasionally for 3 years.

What Do They Eat?
Brook Sticklebacks are mainly carnivorous ("meat eaters"), but they also sometimes eat algae. The usual diet includes acuatic (water) insect larvae, terrestrial (land) insects, waterfleas, worms, snails, and sometimes fish eggs.

What Eats Them?
Despite the sharp spines on their backs, brook sticklebacks are eaten by many other fish species. These include brook trout, largemouth and smallmouth bass, northern pike, yellow perch, walleyes, and bowfins. Fish-eating birds are also a big predator of this fish. They include herons, kingfishers, mergansers, and terns.

How Do They Reproduce?
Brook sticklebacks spawn in late spring and early summer in Minnesota (late May through June). Water temperatures must be above 10° C (50° F) but below 20° C (68° F) for good spawning. Males pick sites in the weeds and create their territories. There, they use algae, sticks, other plant matter, and their own sticky secretion to build a nest almost the size and shape of a golf ball. It has an opening at one end and is attached to the stem of a plant. When a female enters the male's territory, he rushes up to get her to go into the nest. He will even push her in the direction of the nest. Once inside of the nest the female lays her eggs and then forces her way out the other side of the nest. The male then enters the nest and fertilizes the eggs. Once he is done with that, he usually repairs the nest to receive other spawning females. Sometimes a male builds a second, larger nest and transfers the eggs to it (carrying them in his mouth). Each female that visits the nest may lay 50 to 100 eggs. The male will guard the nest and young until he loses control of the school of young fish.

Conservation and Management
Brook sticklebacks have no special conservation status in Minnesota. They are probably important as natural controls for mosquitoes and make an interesting aquarium fish.