The gudgeon is distributed throughout most of Europe and into Russia, but it is not native to Ireland. Although it is an introduced species, gudgeon are considered benign as they have no significant impact on native species or ecosystems. They are thought to have been introduced as live bait and have a patchy distribution around Ireland, mostly in rivers and canals around the Midlands and border counties.
Gudgeon are small, rather pretty fish, with iridescent silvery purplish scales and dark streaks on their backs and tails. They often form shoals and can communicate with each other by making a squeaking sound. Gudgeon have downwards facing mouths with a pair of whisker-like barbels that they use to forage for insect larvae, crustaceans and molluscs on the bottom, especially in shallow water.
Gudgeon spawn at night in the early summer, and their eggs stick to rocks and plants until they hatch. Gudgeon typically live for three to five years and rarely exceed 20cm in length.