Rotifers considered as one of the important zooplankton in the ecological
system of fresh water lakes. It’s an essential food for many species of fish. So,
it’s important to be available all over the year with enough abundance. In the
predator pre
sence, polymorphism is considered an effective way for the species
protection. For that reason, one spine or more of the studied species (Keratella
cochlearis, Brachionus calyciflorus) are being built at the same time where the
predator (Asplanchna priodonata or different species of crustaceans) are in the
lake. These spines usually disappear during the predator absence. This study
also reveals that there is no clear role for the temperature or abiotic factors in
the polymorphism operation.
