The ninespine stickleback (Pungitius pungitius), also called the ten-spined stickleback, is a freshwater species of fish in the Gasterosteidae family that inhabits temperate waters. Widely but locally distributed throughout the UK and along the Atlantic coast of North America, it is also found in many northern and eastern European countries, in Greenland and in Turkey, and in the Far East. Despite its name, the number of spines can vary from 8 to 12.
It lives in extremely weedy ditches and rivers as its small spines do not offer much protection. They have scutes or bony plates all the way down their body.
During the breeding season (April to July), the male develops a black belly and builds a nest suspended on a piece of waterweed, about an inch or so above the substrate at the bottom. The female is attracted over by the male and she lays eggs inside the nest. The male guards these eggs and the young fry when they hatch. Then when they have their spines he drives them away to look after themselves.
Source: en.wikipedia.org/wiki/Ninespine_stickleback - 07.12.2011
With a size of roughly 6 centimeters the Ninespine Stickleback is even smaller than portraited here.