Issyk-Kul Scaleless Osman
Status: 2 [CR: D]. Lake form, very rare, critically endangered. Endemic, has higher growth rates compared to other forms.
Brief description of the adult form. The body is moderately compressed laterally, bare, with scales only along the lateral line, around the anal opening, and the anal fin. On a silver or golden background, there are spots of brown or bluish-gray color. A large fish, reaching 60 cm in length [10].
Distribution general and in the country. Areas of the northern, western, and southern regions of Lake Issyk-Kul and its tributaries [3].
Habitat. Areas where tributaries flow into the lake.
Population. In the first half of the last century, the catch volume reached 700-800 centners/year, in the 60s - only 20 centners. Very rarely encountered, especially in recent years.
Life cycle (lifestyle). Males reach sexual maturity at 4-5 years of age with a length of 18-22 cm. Females mature at 5-6 years. Spawning is partial, extended over time (from April to September), occurring in shallow areas on "snags." The fecundity of females weighing 200-2000 g ranges from 4000 to 32,700 eggs. The highest fecundity is observed in large producers - individuals weighing 1000-2000 g. Feeds on filamentous algae, chara shoots, and zooplankton. Adults prefer zoobenthos - mollusks, amphipods, mysids [2].
Limiting factors. Late attainment of sexual maturity [2, 3]. Unregulated fishing. Deterioration of natural spawning conditions. Possibly, the pressure from introduced predatory fish species.
Breeding. To artificially replenish the fishery stock, in 1965, the Ton fish hatchery was built on the southern shore of Lake Issyk-Kul. The biotechnics of artificial breeding were developed by A.O. Konurbaev [2]. Currently, artificial reproduction is not being carried out.
Existing conservation measures. Since 1966, fishing has been prohibited, but the population continued to decline and is currently very low.
Recommended conservation measures. Resumption of artificial reproduction, prohibition of fishing during the spawning period, declaration of a 5-year moratorium, protection in reserve areas. Establishment of mobile artificial reproduction points, continuation of research on the distribution of the species in the lake, and development of proposals for the creation of specially protected areas.
Кёк чаар, Ала буга
Issyk-Kul Scaleless Osman
Diptychus dybowskii lansdelli Gunther
Status: Category 2 [CR: D], rare critically endangered subspecies (limnicolous form) of Tien Shan sub-endemic species. The subspecies is endemic to the western, northern, and southern parts of Issyk-Kul Lake and corresponding inflows. It is a large fish, up to 60 cm in length and 16 kg in weight; young fish feed on filamentous algae, stonewort, and zooplankton, while mature fish prefer zoobenthos (shellfish and crustaceans). Males achieve sexual maturity at 4-5 years, with a body length of 18-22 cm; females mature at 5-6 years. Females weighing 0.2-2.0 kg have a fecundity of 4,000 to 32,700 eggs; the spawning period is from April to May. In the first half of the last century, the annual catch was 0.7-0.8 tons; in the 1960s, it was only 0.02 tons. Despite the prohibition of fishing for Scaleless Osman in Issyk-Kul Lake in 1966, the stock is declining, and in recent decades, the species has become very rare. Limiting factors include late sexual maturity (long ontogenesis), unregulated excessive fishing, deterioration of spawning conditions, and possibly the impact of introduced predatory fish. In 1965, the Ton fish farm was created for the artificial support of the natural propagation of the species; there is a developed technology for breeding, but currently, the species is not bred. It is recommended to conserve this species, resume breeding, prohibit fishing for five years, and protect spawning and feeding sites.
