Diptychus is a genus of freshwater fish of the carp family. The body is covered with scales or naked or scales are present only in some areas. The mouth is lower, in the corners of a pair of antennae. They inhabit mountain water bodies of Central and Central Asia. Body length 45-50 cm, weight 1-3 kg. 3 species. The best known are Diptychus maculatus, occurring in the upper reaches of the Syr Darya, Chu, Ili, and rivers of the Issyk-Kul basin, and Gymnodiptychus dybowskii, inhabiting water bodies of the Issyk-Kul, Balkhash, and Alakol basins, as well as rivers of Central Asia. It is represented by river and lake forms. Diptychus maculatus matures in 2-4 years, naked - in rivers - in the fourth-fifth year of life, in lakes in 7 years and more. Eggs are bottom-dwelling, hatched on stony ground. Juveniles feed on plankton and aquatic vegetation, while adults feed on benthic organisms and partly on fish.
Adult Diptychus is up to 50 cm long and weighs up to 1 kg. It feeds on vegetation and invertebrate animals. Spawns in spring through summer. Its dwarf form - Diptychus sewerzowi - does not exceed 25 cm in length and weighs up to 200 g. Diptychus dybowskii inhabits mountain rivers and lakes; has 2 forms: river and lake; length up to 60 cm, weighs up to 3 kg. The most numerous was noted in Lake Issyk-Kul, where it served as an object of fishery. Like the marinka, mustache and temmuli, the eggs and innards of the osman are poisonous. It should be taken into account that osmans, or Altai osmans, are sometimes also called fish of the genus Oreoleuciscus.