but they reached their
autumn minimum when the number of copepoda was maximum value. It is known that protozoa serve as
major food items for the macro-zooplankton [19]. Godhantaraman and Uye [20] reported the dominance
of microzooplankton to their ability to exploit smaller food particles unavailable to most
mesozooplankton, particularly copepods. Modenutti et al. [21] found that the presence of some rotifersand copepod species depressed the numbers of ciliates in Lake Rivadavia, Argentina. In the present study,
the density of protozoa was recorded to annual average 8515ind./l in the lake. In general, smaller
protozoan species such as Tintinnidium fluviatile and Askeuasia sp. dominated the protozoan community
of Hulun Lake. Protozoa is regarded by many authors as being a good indicator of organic pollution [22-
24]. Whink et al. reported the shift to smaller zooplankton in Lake Victoria to increased eutrophication,
resulting in a shift from diatoms to cyanophytes[25].