Preliminary report on zooplankton migrations in certain bodies of water of the middle Parana basin

Abstract

Investigations were made in order to establish the existence of vertical and horizontal zooplankton migrations in some bodies of water of the middle Parana basin and if this factor would affect the standing-crop estimations when only surface samples are taken, as is usual in shallow waters. For that purpose, samples in two bodies of waters of different characteristics were taken at different places, levels and hours, especially referred to their extension, depth and hydrophytia. Observations indicate an evident vertical movement, and irregularities in the horizontal distribution that must be taken in mind when careful results are desired.