Threespine Stickleback

Threespine stickleback 

Gasterosteus aculeatus 

A stickleback is another one of those fish that everyone seems to have heard of but they don't know much about. Sticklebacks really are very interesting little critters, with an emphasis on little. Probably, most anyone who has spent any time peering into the edge of a small pond or lake in Alaska has seen sticklebacks but they are often dismissed as just aminnow. So what makes them interesting? First, they are definitely not a minnow. 

As many as 60 species of sticklebacks have been described worldwide but for every actual species there may be  more than one developmental form that may have been misidentified as another species. So it is most likely that there are fewer than 60 species. Nevertheless, five species are recognized in North American waters. Of these, two are found in Alaska, the threespine stickleback and the ninespine stickleback. Sticklebacks may be found in marine, brackish, and freshwaters with both anadromous and nonanadromous forms. The life histories of the threespine stickleback and the ninespine stickleback are generally similar, but the ninespine stickleback is not anadromous and it is more widely distributed in Alaska than the threespine stickleback.  Where both species are present, however, the threespine stickleback is typically more abundant. 

Sticklebacks are small fish. Adults range in length from about one and a half inches to a trophy-class size of about four inches in length. They are weak swimmers and they have no scales. 

Think about this. Here is a small fish that has no scales and cannot swim well. Where would you expect to find this fish? In a bigger fish’s stomach. Well, yes, but there is more to this story. 

Although sticklebacks do not have scales, they do have other good defenses. some, including the threespine stickleback, wear a body armor of hard bony plates that cover most of the body. And they also have several—up to about a dozen—very sharp spines which they can lock into a rigid, upright position. Some point upward and some point outward. The actual number of spines and plates vary between species and populations of the same species. After a predator tries to swallow one or two, it usually learns to leave others alone. 

Different populations of threespine stickleback can have fully marine, anadromous, or fully freshwater life forms. The marine type is the least common. Within each of these types, populations may evolve the size and distribution of plates and other body features, depending on local conditions and predators.  Marine and anadromous threespine sticklebacks are normally larger and have fully developed plates along their entire side.   

In Alaska, threespine stickleback are found mainly in coastal drainages and nearshore waters from Norton Sound and south, including the Alaska Peninsula and Aleutian Islands, though a few populations are found along the coast of the Arctic Ocean. Sticklebacks are among the most abundant freshwater fish in Alaska. Sticklebacks are also found farther south to central California and freshwater forms are found as far south as Baja California. Populations occur in the Great Lakes and on the Atlantic coast of North America, as far south as Chesapeake Bay. They are also found in northern Europe and Asia with a few freshwater populations around the Mediterranean Sea. 

Threespine stickleback spawning is in spring and early summer after an inshore movement from offshore to shallow, still water areas. Males establish and defend territories and develop bright red spawning colors. Territories are vigorously defended with ritual displays, biting, and chasing. Dominant males build nests for spawning. Not like a bluegill or a trout, but like a bird. Sticklebacks are usually found in or near weeds and, as spawning time nears, the male takes bits of weeds and glues a nest together with a secretion from his kidneys.  The nest is a cylindrical or tube-shaped affair with a horizontal orientation. If vegetation is absent, spawning is over sandy areas. 

After the male has built a nest, he looks for a bit of companionship. His eyes turn bright blue, his body color darkens and his sides turn blue, green, and bright red; then, he begins a dance. When a female comes near, this courtship dance intensifies with zigzag motions and head-wagging, and, in his frenzy, he stands on his head to entice her into the nest. Finally, she enters the nest and quickly lays some eggs which the male fertilizes. Abruptly, the female departs and the male takes over to guard the incubating eggs until they hatch. 

Sticklebacks are not prolific. Each female lays only about 80 to 1,000 eggs. But they don't need to be prolific because usually they occur in large numbers, the nest is secure and the male is a good guardian as he fans the eggs with his fins. Hatching occurs in about 7 to14 days in Alaska, depending on local conditions. The hatchlings are smaller than a quarter inch in length and they remain in the nest until they absorb their yolk sac. After they are free-swimming, they remain with the male for several days before they disperse. Afterwards, the male may build a new nest and attract a new mate. 

Threespine stickleback typically do not live long. In most populations they mature, spawn, and die in their second summer though some fish may live to two or even three years old.  The oldest known sticklebacks are around five years old.  Marine and anadromous threespine sticklebacks grow to a larger size. 

Threespine stickleback have small, weak mouths, so they feed on small, weak prey but their bodies are shaped to allow them to slip quietly through their weedy habitat, where they find a wide variety of food items including plankton, small mollusks, and insects.  Historically, sticklebacks have been considered competitors for food with juvenile sockeye salmon but this has not been supported by research. 

Sticklebacks have little direct importance to humans but historically, there have been some limited commercial stickleback fisheries for rendering into oil. Nevertheless they are still of special interest. 

Sticklebacks are eaten by many species of birds and other predators. In some lakes, they may be eaten in large numbers by fish such as rainbow trout and northern pike, usually in situations where there are large populations of sticklebacks and limited amounts of other prey. Some colleagues have told me that stickleback spawning aggregations in Karluk Lake are so dense that grizzly bears scoop them up for food. Ship Creek, in downtown Anchorage, had been previously named Stickleback Creek or Needlefish Creek in the Den’ina language. The stream was important because the anadromous run of sticklebacks was the first opportunity for a fresh protein source after a winter of limited resources and near starvation. 

Some research scientists have serious interest in sticklebacks.  With their rapid generation rate and variable characters, sticklebacks are excellent study specimens to learn about the effects of habitat and communities on evolutionary changes. Sticklebacks are also widely studied in many other fields of research including behavior, genetics, toxicology, developmental biology, biomedical biology, and ecology. 

References: Bell and Foster, 1994; Kari and Fall, 1987; Morrow,1980; Mecklenburg, et al. 2002; Paxton and Eschmeyer, 1994.