MILSTEIN, A., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Israel
HEPHER, B., Agricultural Research Organization, Fish and Aquaculture Research Station, Dor, Israel
TELTSCH, B., Mekoroth Water Co., Central Laboratory, Nazareth, Israel

Abstract. Interactions between fish species as to their effect on the zooplankton populations in the ponds were studied in ten ponds of 0–1 ha each. The ponds were stocked with bottom‐feeding fish: common carp, Cyprinus carpio L., and male hybrid tilapia Oreochromis niloticus L. ×O. aureus (Steindachner), and a filter feeder: silver carp, Hypophthalmichtys molitrix (Valenciennes), at varying proportions. A Principal Component Analysis of the data showed that the fish combination present in the pond accounted for 30% of the overall variability, through the first two components. The first zooplanktonic component (ZC1) can be considered as expressing community structure, showing high zooplankton diversity on one pole and low diversity on the other. The second component (ZC2) is related to the time of appearance of certain zooplankton groups. The most striking differences occurred between ponds with and without silver carp. The presence of the other bottom‐feeding fish caused a reduction of zooplankton diversity, but not so pronounced as that of silver carp. The interactions among silver carp, zooplanktonic trophic groups and algal size are discussed. It is concluded that the effect of silver carp on the zooplanktonic community is a compound one, which includes both direct predation and depletion of their food resources. Copyright © 1985, Wiley Blackwell. All rights reserved