Abstract: Since direct acoustical recognition of concentration layer of copepods C. euxinus, swimming trajectories of chaetognaths S. setosa in the Black Sea were studied using an echosounder at 120 and 200 kHz and ADCP (Acoustic Doppler Current Profiler) at 150 kHz. Sagitta setosa were acoustically discriminated with respect to vertical migration and vertical distributional range depending on stage status in months. C. euxinus were acoustically discriminated with respect to vertical migration and swimming speed, according to dissolved oxygen (DO) concentration and the timing of migrations. Upward migration was completed in about 3.5 h, starting 2.5 h before and ending 1h after sunset (average rate: 0.95 cm s⁻¹) in summer. Species ascended discretely from the suboxic to the lower boundry of the cold intermediate layer (CIL) at 0.82 cm s⁻¹, and passed up the CIL and thermocline fast (2.3 cm s⁻¹). Downward migration took less time (2 h), starting ~1 h before and ending ~1 h after sunrise. Swimming speed within the thermocline and CIL was 2.7 cm s⁻¹; copepods subsequently returned to daylight depth at a sinking speed of 0.57 cm s⁻¹. Chaetognaths were migrated daily between subsurface and oxycline or suboxic zone (OMZ). The lower limits changed to be the oxycline and OMZ depending on abundance of adult and immature (young) individuals in the concentration layer. In July and September, individuals of a new generation did not migrate and stayed in subsurface water. During January through May, all adults exhibited diel vertical migration and co-existed with the copepod C. euxinus during the day time in the OMZ while during June through October, two different layers of S. setosa underwent during their diel vertical migration: The upper layer was immature individuals and the lower layer was mature individuals.