The distribution and relative abundance of fish eggs and larvae encountered at the mouth of Coleroon Estuary has been studied.

Eggs of Stolephorus sp., Cynoghssus sp., Mugil cephalus, Thryssa sp., Sardinella sp. and the larvae of Stolephorus sp., Ambassis commersoni, Therapon sp. and Alectis indicus have been collected and identified.

Hydrographical parameters such as temperature, salinity, pH, rainfall and dissolved oxygen were also recorded simultaneously to understand the influence of these parameters on the distribution and abundance of Ichthyoplankton.

The results of the present study indicate the abundant occurrence of fish eggs and larvae during March and April; however an inverse trend was earlier observed by Venkataramanujam and Thangaraja at Vellar Estuary during the same period, which may perhaps be due to the bar-built mouth which is reduced to a small stream during summer, when freshwater inflow is nil. The Coleroon Estuary, on the other hand, is wide open, year-round and hence these two estuaries appear to be distinct from each other hydrobiologically.