The nine-spine stickleback, Pungitius pungitius, is Britain’s smallest freshwater fish and one of the toughest, able to withstand oxygen-poor water and a variety of temperatures.
Like its more numerous cousin, the three-spine stickleback, the males play a significant role in the breeding process. They build a nest and, once the female has laid her eggs, the males protect them from predators.
Using their fins, they channel freshwater through the nest to make sure there is a good oxygen supply. When the young hatch, they continue to protect them, herding them together and taking on any creature that tries to eat them.
Once the young develop their own spines, parental duties cease and the young are driven away.
Considering the fish is only 8cm (3in), defending their young can be a dangerous business. Although their spines lock upright to prevent them being swallowed, they are not as prominent as those of the three-spine variety.
The males do not turn red for danger in the breeding season like their larger cousins, only going dark underneath and lighter above.
Although they are called nine-spine, they can have anything from eight to 12 spines. They live in ponds, lakes, rivers and estuaries, and are often the first fish to colonise once-polluted waterways.
