Fisheries research was carried out on the Khantayskoye reservoir in 1977–2020. This article presents the results of these works. In the first years after the flooding of the Khantayskoye reservoir, pike and common species of whitefishes (Siberian vendace, peled and whitefishpyzhyan) constituted the basis of the fishery. The share of other fish (carp, burbot, perch) was insignificant. The sharp increase in the food supply for planktophages and benthophages was short-term. Trophic depression began to appear in the early 80s (3–5 years from the moment the reservoir was filled). From this moment to the present time, whitefish species have a slowdown in linear and weight growth, an increase in the timing of puberty, a decrease in fertility. Of the whitefish fish, only Siberian vendace and whitefish are present in the fishery, the numbers of which have significantly decreased. Since the mid-2000s, the number of peled has decreased significantly and this species of fish has become rare in the reservoir. . Currently, there is a relatively high number of pike. Roach, ide, pike and perch actively mastered the channel of Kontiki, where before was practically absent. The increased number of these species affects the number of whitefish in their spawning areas, and their reproduction, including the safety of eggs.The parasite fauna of the main commercial fish species of the Khantayskoye reservoir was investigated. The most pathogenic were myxosporidia Henneguya zschokkei (Gurley, 1894), the causative agent of peptic ulcer disease in whitefishes.

A comparative analysis was carried out investigating the parasite faunas of coregonids (humpback whitefish, peled, least cisco, and tugun) from the Lower Ob Ural tributaries (Rivers Synya, Voykar, Severnaya Sos'va, Sob, Shchuch'ya) and from the Khatanga River. Surveys revealed 48 parasite species, most with a complex life cycle (29 helminth species and 3 myxosporidian species whose development involves benthic organisms). Semianadromous whitefish spawning in Lower Ob tributaries were shown to have a poorer species composition of parasites (13-16 species) compared to land-locked whitefish from the Khatanga (23 species). The parasite fauna of semi-anadromous peled from the Lower Ob had the most diverse species composition among the rest of coregonids, with relatively high similarity between the rivers Voykar and Synya, while that of the S. Sos'va River stood apart. Resident ecotypes of peled from the rivers Shchuch'ya and Khatanga were similar in the species composition of their parasites in spite of the substantially different geographical locations of the catchments. Least cisco within the Lower Ob basin (Rivers Voykar and Sob) featured a high similarity of the parasite species composition, which was, however, very different from that in least cisco from the Khatanga. Some freshwater parasites (infusorians, monogeneans, trematodes and leeches) apparently get lost in the brackish waters of Khatangsky Bay, while the crustacean Coregonicola orientalis is introduced into the river during the spawning run. The parasite fauna of tugun was the richest in the Khatanga (17 species), relatively poor in the Sob (5) and Shchuch'ya (6 species), and generally reflected the features of the fish ecology in each specific river. K e y w o r d s:

The results of ichthyological and parasitological studies of the Kureiskoye reservoir are presented. The features of the formation of ichthyofauna during the formation of a reservoir and its industrial use are shown. The ichthyofauna of the Kureiskoye reservoir was formed on the basis of the indigenous fauna of the river. Kureyki. The modern composition of fish includes 22 species. Grayling fish are represented only by the Siberian grayling — Thymallus arcticus (Pallas, 1776). This species has a relatively small number of scales in the lateral line (no more than 95). Grayling is found in Lake Munduyskoye, which on average has about 100 scales. Since Munduyskoye Lake belongs to the river basin Kureyka, we believe that the second species, the black Baikal grayling Th. baicalensis (Dybowski, 1874) is also present. The main processes of its formation took place as in the Khantaskoye reservoir. Currently, the number of salmon and whitefish is decreasing. These groups of fish previously formed the basis of the composition of the original ichthyofauna. Today salmon and whitefish are found in the zone of backwater and flooded tributaries of river channels. The composition and number of whitefishes has changed especially. Tugun practically disappeared, others (peled, wild boil, vendace, and whitefish) began to be found singularly. The dominant role is played by pike, which uses peat islands for its spawning, as well as perch and roach. The transformation of the reservoir led to radical changes in the composition and structure of communities of all groups of organisms in the aquatic biota. This influenced the composition and abundance of fish parasites. The parasite fauna of the fish of the Kureyskoye reservoir is represented by widespread species of helminths. Infection with helminths mainly occurs when fish feed on planktonic crustaceans.