Effects of Untreated Domestic Sewage on Zooplankton Collected from Vellar Estuary

The present study revealed the deleterious effect of untreated domestic sewage on plankton. The different groups of zooplankton tested for sewage toxicity showed a tolerance range of 23.5 to 45%. Based on the 24hr LC 50 values among the zooplankton, it was found that the Centropages typicus (copepod larva) was the most sensitive species (23.5%), Zoea larvae of the hermit crab, Clibanaius olivaceous (32%) and the larvae of prawn Penaeus indicus (38%) were moderately tolerance and the icthyoplankton, Ambassis commersonii (43%) and Therapon jarbua (45%) were the most resistant ones. Between the two species of ichthyoplankton tested, Therapon jarbua was more tolerant than Ambassis commersonii.