Threespine stickleback

Those spines aren't there just for looks

Even though we call them threespine sticklebacks, these fish can sport two to four spines on their backs (but three is the average). Sharp spines and large bony side plates provide essential armor against predators for these slow-moving fish. The spines can be locked in an erect position, making the animal extremely hard to swallow.

Dad's the king of his (seaweed) castle
In early spring and summer, male sticklebacks begin creating nests. They dig a small pit in the sand, then construct a spherical mass of plant material and debris, glued together with a substance the male produces from his kidneys. Afterwards, he bores a small tunnel in the sphere by swimming vigorously through it. All this takes five to six hours.

Once the nest is ready, the male begins a zig-zag dance to attract females. His throat turns a bright red; studies have shown that females prefer males with brighter red colors. This may be because males with more intense colors are better at finding food and could pass that trait to their young.

Eventually a female will follow him into the nest and lay between 40 and 300 eggs—the male then returns to fertilize them. From that time on mom goes her own way, but dad stays behind to fan the eggs (providing them with oxygen) and to protect them from predators. He continues caring for the young fry after they hatch and even teaches the little ones self-defense by chasing them around!
Celebrate stickleback diversity!
Threespine sticklebacks come in many varieties—some live in freshwater and feed at the surface of lakes and streams; other freshwater types prefer to feed at the bottom. But some spend most of their adult lives in the ocean, returning to fresh or brackish water only to breed.

The freshwater sticklebacks probably evolved from saltwater types after being stranded in lakes during the last glacial melt. There are so many variations of threespine sticklebacks that some observers claim there is a different subspecies in almost every lake in the Northern Hemisphere!
A researcher's dream
Because of all the variations developed over time, evolutionary biologists love to study how these small fish have adapted to different environments. But that's not all—researchers also are interested in their breeding and social behaviors, and how the fish work together to protect themselves against predators. The fact that the fish are easy to collect, easy to keep in aquaria and can be found in northern oceans and low-elevation fresh water from Asia to Europe to North America, also make them popular research subjects.


 Threespine stickleback range

Quick Facts

Diet: Carnivore
Size: 2”-4"