Stickleback

Sticklebacks are fish from the family Gasterosteidae. There are 16 acknowledged species in five acknowledged genera, although recent discoveries have called the precise definitions into question. An unusual feature of sticklebacks is that they have no scales, although some species have bony armour plates, and strong and clearly isolated spines in their dorsal fins, hence the name. They are related to pipefish and seahorses.

Sticklebacks are most commonly found in the ocean, but some can be found in fresh water. The freshwater taxa were trapped in Europe, Asia, and North America after the ice age, and have evolved different features from the marine species. Sticklebacks are carnivorous, feeding on small animals such as insects, crustaceans and fish larvae.

In their mating behaviour, unusual among fish, the males construct a nest from vegetation held together by secretions from their kidneys, then attract females to the nest. The female lays her eggs inside the nest where the male can fertilise them. The male then guards the eggs until they hatch.