116: Brook Stickleback

An interesting little fish closely related to the seahorse

Sticklebacks are a family of small fish who inhabit the temperate zones of the Northern Hemisphere. Most live in saltwater oceans but a few species live in freshwater, including the Brook Stickleback, which lives in Colorado, and might even be a glacial remnant that has lived here for 20,000 years – or might be a recent migrant, introduced from a bait bucket in the 20th century. No one is sure! In Colorado, they live in the South Platte basin, and are threatened by dam construction and habitat destruction.

Sticklebacks are characterized by having 2-10 unconnected dorsal spines which project from the top of the fish. They also do not have scales. Wait – record scratch – what? I thought all fish had scales! Turns out, no no no. I think we’ve talked before about how the category “fish” is extremely diverse, even including some animals (agnates) which are technically vertebrates but have a piece of cartilage instead of a spine. Scales on most fish are protective structures that grow from the dermis, and are probably the evolutionary root of teeth and hair in other vertebrates, including humans. Scaleless fish have simply evolved different protective structures. For example, catfish have a layer of mucus that can sense chemical changes in the water around them rather than scales. As far as sticklebacks go, some have developed bony armor plates on their bodies – not the kind that live in Colorado, though.

Sticklebacks also have distinctive personalities. A recent study found that, as social animals who live in groups, individual sticklebacks can display shyness, boldness, and understanding of social dynamics and group leadership.

Sticklebacks are closely related to pipefish, sea dragons, and seahorses, so their hands on parenting methods may be familiar to you if you know about seahorses. During midsummer spawning, males secure a territory and build a nest from algae and aquatic vegetation. The nest has a single entrance. After mating, the males provide protection for the eggs. Eggs take around 10 days to hatch. Baby sticklebacks are then carefully watched over by the male, who will allow them to wander beyond the nest but then scoop them up in his mouth and deposit them back in it if there is a threat or if they wander too far.