Vibrio cholerae O1 was found to be associated with six groups of zooplanktons during the study period. The study revealed that V. cholerae O1 had maximum association with rotifer (60.4%) and nauplii (76%) and minimum association with cladocera (3.39%). Vibrio cholerae O139 was also found to be associated with six groups of zooplanktons in three studied sites during the study period. The data revealed that V. cholerae O139 had highest association with rotifera in all sites (79.5%, 76% and 77.7% respectively) and lowest with copepod (2.46%) and ostracoda (2.69%). Zooplankton had more or less two peaks of swarm or bloom like from February to April (postwinter or spring) and September to November (pre-winter or autumn) which coincides with two seasonal cholera epidemics in Bangladesh. The findings therefore suggest a correlation between cholera epidemics and zooplankton bloom.
