Gut pigment and abundance of the female Calanus euxinus (Hulsemann) were measured from several water layers (defined by density values), with 3-5 h intervals during 30 h and 21 h at a station in the southwestern Black Sea in April and in September 1995, respectively. The female C. euxinus was observed to begin migration to the upper phytoplankton-rich layer approximately 3 or 4 hours before the sunset. Only a fraction of the female Calanus population (0.2% in April and 3.6% in September) did not migrate but remained at the depth of the oxygen minimum zone during the nighttime. The migrating population was determined to have spent 7.5 h in the euphotic zone in April and 10.5 h in September. The grazing rate of female Calanus euxinus was measured from the gut content data collected from the layers which contain the euphotic zone. The percentage of primary production grazed by the female C. euxinus was calculated as 14.5% in April and 9.5% in September.