Here’s a Valentine’s Day fish for you – a fish that literally builds its own love nest. The three-spined stickleback and its subspecies are spread out across many coastal waters of the northern hemisphere. It’s very adaptable and can live in fresh, brackish or salt water.
One of its most striking characteristics is on display during the breeding season. During this time, the male’s belly acquires a bright red color, his back glows intensely silver, and his eyes become blue. This species also display a very elaborate breeding behavior. In springtime, the male stickleback begins to gather leaves, algal filaments and other plant material in order to build himself a nest over a small pit that he has dug out. He glues all of these materials together with spiggin, a substance secreted from his kidneys. Once the nest is complete, he waits for a suitable mate, while at the same time guarding his territory ferociously. Whenever a potential partner shows up, he courts her with a kind of zigzag dance to try to convince her to visit the nest and lay her eggs. After he fertilises the eggs, his paternal instincts drive him to not only chase the female away, but also all other fish that approach the nest.
He takes care of the eggs by fanning them, meaning he positions himself in front of the eggs and moves his fins in order to bring water into the nest, and with it, oxygen. After a little more than a week the eggs hatch. Even though the male tries to keep them in the nest by sucking up any escapees in his mouth and spitting them back into the nest, in the end, the young ones win and leave him for the freedom of their own lives.