Studies on the biology of mullets in the Kayamkulam Lake were conducted with emphasis on growth and feeding habits.

The occurrence of mullet fingerlings in large numbers with Mugil troscheli Bleeker, as the dominant species from October to March and their sudden disappearance after March attracted the attention of the author. An attempt was made to analyse this phenomenon based on the study of their habits. The data collected indicated that 1 - 3.5 cm length groups are mainly plankton feeders forming large surface shoals locally called ' Thuli'. The stomach contents of 4 - 5 cm length groups showed for the first time spirogyra filaments and bits of aquatic weeds, apparently indicating that they have partially adapted to a semidemersal habit. In 5.5 - 7.5 cm and above length groups, the food mainly consisted of Oscillatoria, Spirogyra, etc. But there was the continuous presence of sand particles and aquatic weed remains. This seems to indicate that the fingerlings have completely given up the planktonic habits and have become semidemersal living partly by browsing on the aquatic weeds and by nibbling at the detritus and films of Oscillatoria found covering the bottom of the lake.