A critically endangered anadromous Acipenser nudiventris (A.n.) –  inhabited many Eurasian rivers. During the program for A.n. re-acclimatization in the Kuban River, where it was extinct, the heterogeneous A.n. broodstock was formed.

The different age-graded offspring from farmed broodstock are released annually: hundreds thousands larvae and dozens mature tagged females and males to natural spawning grounds 200 km above the upper dam in protected natural zones;
and thousands juveniles, 2-4 years old - into the Krasnodar reservoir.

From 2018, there has been a passage of mature A.n. breeders from the river by fish lift through a dam into the reservoir headwater.
Analysis of previous publications showed that in natural propagation conditions in the Kura and Ural rivers different age-graded A.n. (residents), grown from juveniles, not run off to the Caspian Sea, were represented mainly by males (till mature), but gonads of few encountered elder females did not developed above maturity stage I. Conversely, mature females dominated in the spawning ship sturgeon contingent, which run to the rivers from the sea (migrants).
These species-specific distinctive features of the behavior and formation of phenotypic groups of A.n. should be considered at recovery of A.n. population.
Therefore, the presentation considers the experiments results on determination the ratio of rheoreaction types of same-aged (60-61 days) A.n. juveniles using a straight-through 10-chambers hydrodynamic "fish pass" with video recording.
Threshold V_t and critical V_k (carrying) water flow velocity for hungry (1-3 days) and fed A.n. juveniles were determined at different lighting.
It was established, that unlike Russian and stellate sturgeons within the velocity range 0.3-0.7 V_k, 5-10 grams A.n. juveniles reliably differed in the ratio of rheoreaction types (against/along the current and finding sections without current).
This may serve as one of the reasons of life history peculiarities for the division of A.n. juveniles into groups (residents and migrants) with different behavioral and settlement strategies.

A. nudiventris, juveniles, behavior experiments, fish passage, rheoreactions, restocking, residents and migrants.