BIOLOGY OF CLUPEICHTHYS-AESARNENSIS (CLUPEIDAE) IN UBOLRATANA RESERVOIR, THAILAND, WITH SPECIAL REFERENCE TO FOOD AND FEEDING-HABITS

The freshwater sardine Clupeichthys aesarnensis is a zooplanktivore li ke many clupeids. In Ubolratana reservoir, Thailand, it feeds selectiv ely on larger zooplankters, especially Cladocera and to a lesser exten t on Copepoda. Other zooplankters are also consumed together with both living and dead insects and occasionally its own young. It feeds duri ng the day. Our results indicate that the slight seasonal differences in food consumed probably reflects differences in availability at diff erent seasons and sites. The fish grows in weight, as expected, at a h igher rate than the cube of its length. The condition factor is the sa me for males and females and shows some seasonal variation. Data on fe cundity and gonadosomatic index mark this fish as highly fecund and a year-round spawner. Its short life span, favourable growth and high fe cundity make it a valuable source of cheap protein. In 1990, 17% (abou t 300 tons) of the fish catch from Ubolratana came from this fish.