Four-hundred Calanus sinicus specimens with food in their alimentary canals were collected in August (Summer, 100 specimens), October (Autumn, 100 specimens) 1992 and February (Winter, 100 specimens) and May - early June (Spring, 100 specimens) 1993, using a vertical haul with a big plankton net (GG 36 mesh, diameter of the net 80 cm, length of the net 260 cm) during the fundamental ecological survey for fishery resource enhancement in the Bohai Sea.

Analysis of the alimentary canal contents of the specimens showed that this species is phytoplanktonivorous, and feeds mainly on diatoms, which occupy 94.6% in its food composition. Coscinodiscus radiatus, Coscinodiscus excentricus, Coscinodiscus sp. and Coscinodiscus asreromphalus are its main prey, occupying 89.2% in its total diet. Although the Calanus sinicus food organism group has certain seasonal variations, it is not very significant. The mean food group replacement rate is only 13.7%. But its food species has clear seasonal changes. The mean food species replacement rate reaches 50.5%. A seasonally decreasing (autumn> spring > winter> summer) pattern of the feeding intensity of Calanus sinicus accords with the seasonal change in the biomass of Coscinodiscus in the environment. Calanus sinicus apparently prefers to feeding on the most dominant and easily available phytoplankton-Coscinodiscus. A notable phenomenon among the zooplankton is that the feeding intensity of predatory species is much higher than that of filter-feeding species.