Gudgeon (Gobio gobio) is a freshwater fish of the gudgeon genus, carp family. It is a gregarious river and lake fish. Leads a benthic lifestyle. Reaches a length of 22 cm and weight of 65-70 g. Its usual size is 9.5-10 cm and 13-20 g. It matures at 2-3 years of age. Spawning is extended in time, eggs are hatched in separate portions in the current, usually in shallow waters, in early May - June, at water temperature of 12-16°C. Spawning substrate is sandy-pebble soils and aquatic vegetation. Absolute fecundity up to 3 thousand eggs. It feeds on zooplankton and benthic organisms, on spawning grounds it eats fish eggs, including its own. It has no commercial importance. It is used as bait for taimen and burbot fishing.
The size is small, but larger specimens are found. Appearance is quite specific: the body is spindle-shaped, slightly flattened on the abdomen side. Scales are large. The snout is elongated, the mouth is lower, the lower lip is interrupted in the middle, in the corners of the mouth there is a well-developed pair of antennae. There are 40-45 scales in the lateral line. The body is greenish-brown above, silvery on the sides, covered with bluish or blackish spots, sometimes merging into a continuous dark stripe, the belly is yellowish. The dorsal and caudal fins bear numerous dark spots. In the water, it is easily recognized by the large, widely spaced apart pectoral fins, which give the body a triangular shape.
Typical bottom-dwelling species, kept in large flocks throughout the year. Inhabits rivers in sandy and stony areas with medium current velocity. Often found in reservoirs, often in lakes and ponds with optimal oxygen regime.
According to the last revision of Gudgeon of the genus Gobio the range is limited to water bodies of the north-eastern part of Europe: Great Britain, southern Sweden, water bodies of the basins of the White, Baltic and Northern seas and the Volga River. Within this range populations are characterized by considerable morphological homogeneity.
It reaches sexual maturity at the age of 3-4 years, when its body length is at least 8 cm. The ratio of males to females is observed to be approximately equal. Spawning is batch spawning, starting at water temperature +7 °C; its total duration is 1.5-2 months. Fecundity does not exceed 10-12 thousand sticky eggs, which are deposited on hard substrates in shallow waters. Eggs are encrusted with silt particles, grains of sand, which makes them invisible. Larvae hatch with large pectoral fins and highly pigmented eyes. They do not react to light and remain lying on the bottom for several days. By the end of the growing season, young fish reach a length of 5 cm. Relates to typical benthophagous: larvae feed on small bottom invertebrates (rootworms, rotifers), young and adult fish consume mayflies and small mollusks, eggs of other fish.