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The paper presents the results of the sterlet sturgeon Acipenser ruthenus reintroduction into the Kama Reservoir (Perm Krai, Russia) by sterlet fry from hatcheries into the reservoir since 2001. The effectiveness of hatchery releases was evaluated by monitoring gillnet sampling 2014–2020. The results showed that the species was reported throughout entire Kama Reservoir, which contrasts with 1988–1994 data, when the species was registered only at the upper part of the reservoir near the Kama River mouth. The highest number and biomass values of catch per unit effort (CPUE) of the sterlet were found in submerged river channels – the deepest habitats with flow conditions which are close to the ecological requirements of the species. The distribution of the sterlet within the channel biotopes of the reservoir is defined by reduced variability. The biggest individuals and the widest size range of the sterlet were typical for the upper area of the reservoir and Chusovskoy Bay, which have the greatest flow. The smallest sizes were typical for fish from catches near the dam of the reservoir, which is consistent with the published data on the distribution of sterlet in reservoir conditions. The presented results may indicate the artificial formation of the sterlet stock in the Kama Reservoir maintained by hatchery releases. The revealed distribution of the sterlet in the reservoir determines the direction of further research on natural reproduction and thus formation of an artificially formed population. Also, future studies are required to assess the possibility of hybridization of the sterlet of artificial origin with natural populations of the species, since the low genetic diversity of the sterlet released into the Kama Reservoir which can lead to irreversible loss of genetic individuality of the natural stocks of the species in the catchment of upper course of the Kama River.

We estimated the proportion of hatchery and natural fall spawning chum salmon returning to the Amur River using chemical markers specific to hatchery-origin fry. We used otolith microchemistry technique to identify fish with artificial origin among returning spawners. First, we found that juveniles of artificial origin had higher values of the Sr:Ca molar ratio of the otoliths’ edge zone compared with juveniles of natural origin, what can be related to the use of rearing feed produced from raw materials of marine origin rich in strontium. Then we observed that most of the spawners from Anyuisky Hatchery and from the Amur River mouth at the start of the spawning migration has also the higher value of Sr:Ca molar ratio of the juvenile zone of otoliths. Also, adults with higher values of the Sr:Ca molar ratio are characterized by a skewed right in the peak of the age distribution. Both, the age structure and phenological shift in the time of spawning migration of individuals with higher value of the used chemical marker corresponds to results of studies on hatchery-produced chum salmon completed at different parts on Northern Pacific. The results of this study will be used in the management of Amur fall chum salmon fisheries, and also demonstrates the necessity of the development of specific measures for increasing the survival of juvenile anadromous salmonids released at large rivers and exposed to prolonged freshwater migration to the ocean. As a further application of the methodology, we plan to identify the markers specific to each of the hatcheries and main spawning tributaries belonging to Amur River catchments. This will be an important step in the evaluation of the contribution of different stocks in mixed fisheries and also in the estimation of the effect of hatchery releases on naturally spawning stocks of Amur fall chum.Following to, our results may indicate the applicability of this approach for the determination of artificial-origin fish in a mixed sample of the Amur fall chum salmon.