Nine-spined stickleback

Identification

The nine-spined stickleback is even smaller than its three-spined cousin — adults average just 5 to 6 cm. The body is slender and elongated, with 7 to 12 short spines along the back (despite the name, there are rarely exactly ten). Unlike the three-spined stickleback, this species lacks the prominent bony lateral plates. The color is olive-green to brown with dark crossbars. During spawning season, males turn jet black with white-edged pelvic fins.

Behavior & ecology

The nine-spined stickleback lives hidden among dense aquatic vegetation, feeding on small crustaceans, midge larvae, and water fleas. It is shyer than its three-spined relative and avoids open water. Like its cousin, the male builds a nest for reproduction, but it hangs among water plants rather than sitting on the bottom. The species tolerates low-oxygen and acidic conditions, allowing it to survive in peat ditches and marshes where other fish species cannot.

In the Netherlands

The nine-spined stickleback occurs throughout the Netherlands but is less common than the three-spined species. It prefers shallow, densely vegetated waters: peat ditches, polder channels, marshlands, and small ponds. The species serves as an indicator for waters with rich bank-side vegetation. It has no closed season and no minimum size, and is not a target for anglers. In the food web, it serves as prey for pike and other predators, but its hidden lifestyle makes it less vulnerable than the three-spined stickleback.