Abstract
Population dynamics of two cladoceran species, Holopedium gibberum and Bosmina longirostris, in Lake Ozenuma were studied during ice-free seasons in 1987 and 1988, and diel changes in vertical distribution of the two populations were investigated in summer. Both species were distributed in the whole water column during July-October, and showed no marked diel vertical migration. The population parameters(density, biomass, %adult, egg ratio, birth rate) were relatively stable. Fish predation pressure seemed high among the H. gibberum population, since mean body length and minimum reproductive length of the animals were markedly smaller in Lake Ozenuma than those reported in other fish-scarce lakes.
