Abstract
The data on hosts of Ellobiopsis in Central Asia waterbodies are nearly non-existent. All research in this direction was conducted in other regions (Europe and Brazil). Parasitological studies were carried out in different seasons in the North and Middle Caspian Sea. Twenty-one taxa were registered in zooplankton, and only dominants of community calanoids Acartia (Acanthacartia) tonsa and Calanipeda aquaedulcis were infected with Ellobiopsis sp. Calanoida C. aquaedulcis was reported for the first time as a host for Ellobiopsis. The number of parasites per host was equal to one. The body length of parasites varied from 0.10 to 0.80 mm. The highest infection degree was recorded in C. aquaedulcis (5.71%), and it varied from 2.61% to 3.35% in Acartia. The individuals in the juvenile developmental stages were infected in Calanipeda, while in Acartia, individuals in all developmental stages were vulnerable to infection. The infected calanids had reduced body lengths. The findings suggest the possible influence of Ellobiopsis sp. on quantitative variables of hosts in the Middle Caspian, especially on biomass, by reducing the body sizes of hosts. However, no effect on the abundance and biomass of the host and the structure of the zooplankton of the North Caspian Sea has been detected.