Polyarthra prefers food in a large size range (approximately 1�C40��m) [37], which enables it to dominate throughout the year.Cladocerans had a negative correlation with rotifer densities in this study. third Planktonic rotifers often are abundant when only small cladocerans occur but typically are rare when large cladocerans are present. Cladocerans share available food with rotifers. The main species of cladocerans are filter feeders [4�C11, 42]. They feed on nanoplankton and other small particles, but cladocerans often show dominance over rotifers due to their large body sizes and other factors [43]. The extremely low density of cladocerans in this lake could be attributed to fish predation. There were approximately 11000kg of fish, mainly composed of silver and bighead carp, released to the lake after it was refilled.

Though the primary purpose of fish release was to inhibit the potential Microcystis bloom by direct predation, the fish also predated the large zooplankton population, especially cladocerans, because of their nonselective filtering habit. The rotifers may benefit from this fish behaviour. The observed copepods mainly consisted of Cyclopoida, which prey on rotifers [44, 45]; however, there was no significant relationship between them detected in our study, most likely due to the low prey pressure on rotifers. It has been often observed that the abundance of rotifers is proportional to the trophic status of a water body [23]. Many rotifer indices were established to evaluate the lake trophic status. The average values of H��, J, and DMg indicate that the lake was somewhat mesotrophic.

However, these indices exhibited poor relationships to TP, TN, and chl.a. Compared to the nutrient concentration, the relatively high index was most likely due to the instability of the lake ecosystem after dredging. According to the intermediate disturbance hypothesis, disturbance should promote biodiversity. Furthermore, a diversity of aquatic environments, such as islands and macrophytes, may provide more niches.More complex indices for rotifers, including the saprobic index and QB/T [5], were established for saprobic and trophic evaluation according to rotifer trophic preference. Some studies have established a linear regression formula describing the relationship between trophic status and the rotifer community index [11, 46].

These indices were reliable in the lakes they studied.However, it is very hard to establish one-to-one causal relationships between rotifer composition and trophic conditions. The responses of rotifers to environmental factors were found to be nonlinear, sometimes unimodal Anacetrapib or bimodal, in our study. Nutrient elements indirectly affect rotifers via the food chain. Moreover, apart from trophic conditions, other abiotic factors [47] as well as food composition (esp.