gudgeon

Gudgeon is a common name for several small freshwater fish in the family Cyprinidae, most notably Gobio gobio, the common gudgeon, which is widespread across much of Europe and parts of western Asia. These fishes are small and slender, typically reaching about 7 to 12 centimeters in length, with a subdued coloration that helps them blend into river and stream substrates.

Gudgeons prefer clear to moderately turbid waters in rivers, streams, and ponds. They occupy a variety of habitats, often favoring areas with gravel, sand, and aquatic vegetation where they can forage along the bottom. They feed on small invertebrates, zooplankton, algae, and detritus, using a subterminal mouth to pick prey from substrates.

In the wild, gudgeons spawn in spring as water warms. They lay adhesive eggs among gravel, vegetation, or roots, with eggs hatching after several days to weeks depending on temperature. Juvenile gudgeons grow rapidly and reach sexual maturity within their first year, living several years in favorable conditions.

In angling, gudgeons are sometimes used as live bait for larger predatory fish, though they may also be released after capture in catch-and-release practices. Beyond fish, the term gudgeon appears in mechanical engineering to describe a gudgeon pin (piston pin) that connects a piston to a connecting rod, and the corresponding gudgeon bearing that supports the pin; the term reflects historical usage in engine construction.

Overall, gudgeon encompasses both a small freshwater fish and, in engineering terminology, a specific type of pin and bearing used in engines.