The genetic structure of crucian carps colonies in Ukrainian water bodies was defined by gene marking. The sexual structure and ploidy were investigated, the duration of spawners maturation, life-span, rate of growth and the linear growth of independent species and biotypes were defi ned. The comparative biological analysis showed that virtually all the researched crucian carps had low linear growth index and early maturation terms. The hybrid individuals of C. auratus–C. carassius during the first years of life were characterized by the high rate of growth which was most likely determined by the “hybrid power” which is kept by this biotype only within the starting phase of existence, aft er which the active growth is signifi cantly reduced. The individual biological peculiarities of peculiar species and biotypes of crucian carps do not depend on their genetic nature but in most cases are defi ned by the external living conditions.