Fish predation pressure on and interactions between cladocerans: Observations using enclosures in three temperate lakes (Germany) and one tropical lake (Ethiopia)

Abstract

Observations were made on the response of cladocerans to fish predation and the interactions among cladocerans using enclosure experiments in three temperate lakes (Germany) and one tropical lake (Ethiopia). In all lakes large-sized cladocerans were removed by fish until small-sized ones and rotifers remained. In apparently all cases the cladocerans of small-bodied species assumed their largest sizes in no-fish enclosures. In fish-enclosures, the small-bodied cladocerans assumed high biomasses due to elevated food resources in the absence of competition from large-bodied cladocerans. It was also observed that in the absence of fish predation, the dominating large-sized species had an excluding effect on other small-bodied cladocerans. In all cases variations between lakes were observed in the behavior of cladocerans even when fishes were absent.