Attempts have been made to correlate the abundance of eggs and larvae of flat fishes belonging to families Cynoglossidae and Soleidae with the hydrographical parameters of the environment, particularly the salinity. The eggs and larvae were found to occur in the Cochin backwater during the pre-monsoon period but not during the south west monsoon period. During the south west monsoon period larvae belonging to very early stages were found at the marine end (Fairway Buoy). The continued or prolonged existance of very low salinity appears to restrict the distribution of flat fish larvae. In the post-monsoon period also the eggs and larvae were not found in regions of very low salinity. Larvae of Cynoglossus puncticeps (Richardson). C. brevis Gunther, C. cynoglossus (Ham. Buch). C. lida (Bleeker) and Solea heinii Steindachner were obtained in the collection taken from the estuary. From the data it is seen that each species has specific spawning period.