BIOMANIPULATION BY ECOTONE MANAGEMENT IN A LOWLAND RESERVOIR

The comparative studies on fry of dominant fish species in the lowland Sulejow Reservoir have demonstrated the importance of an unstable eco tonal shoreline zone in whole system dynamics, which affects water qua lity. Ecotone zone utilization by fish determines their reproductive s uccess and consequently pressure of fry on a zooplankton community. De nsity of perch, which dominates in the fry community of the Reservoir, influences the utilization of ecotonal resources by dominant cyprinid fry-roach. A reverse relationship between perch and roach fry densiti es has been demonstrated, which in turn, affects utilization of zoopla nkton by roach fry. At stations of highest perch density roach reduces feeding on zooplankton and eats more algae and insects. The knowledge of competitive relations between perch and cyprinid fry has been an i mportant aspect of application of the biomanipulation concept in the r eservoir ecosystem, to improve fish yield and water quality. Hypotheti cal models of energy flow through the reservoir's ecosystem with poor and well developed flooded riparian ecotonal zones are established.