The redfin (cardinius erythrophthalmus) is a freshwater fish of the redfin genus of the carp family. The body is tall, the mouth is terminal, facing upwards. It inhabits water bodies in the basins of the Baltic and southern seas of the country. It is a lake fish, less often a river fish. Matures in the third to fifth year of life. Spawning is batch spawning in April-June. Eggs are hatched on vegetation. Fecundity from 90 to 400 thousand eggs. It feeds on aquatic vegetation, bottom invertebrates, eggs and young fish. Cardinus erythrophthalmus is of local commercial importance.

Typical gregarious fish species, inhabits lakes and rivers flowing into the North, Baltic, Black, Azov, Caspian and Aral Seas. Introduced by humans to Ireland, Morocco, Madagascar, Tunisia, New Zealand, Canada, and Spain. In New Zealand and Canada, it is considered a nuisance species, displacing native fish species. The main habitat of the redfin is bays and river channels, as well as flowing ponds and lakes, where reeds, reeds and other aquatic plants grow in abundance. Here it is quite often found in community with crucian carp, tench and bream and leads an almost sedentary life, rarely moving away from its chosen place.

Externally, it resembles roach. The easiest way to distinguish it is the golden color of the scales and fiery red fins. And also the color of the eyes: in redfin - the eyes are orange, with a red spot at the top, while in roach - blood-red. Another difference is the number of soft rays on the dorsal fin: the redfin has 8-9 of them, while the roach has 10-12. Sometimes there are hybrid forms of these fish, possessing features of both species. The body length can reach 51 cm, and the maximum known weight is 2.1 kg; the usual size is 16-19 cm and weight 100-300 g. Life expectancy is up to 19 years. The body is slightly flattened on the sides and covered with relatively large scales. One dorsal fin. The anal fin has 3 hard and 8-12 soft rays and 36-39 vertebrae.