THE DIETS AND RELATED ASPECTS OF FEEDING OF NILE TILAPIA (OREOCHROMIS-NILOTICUS L) AND COMMON CARP (CYPRINUS-CARPIO L) IN LOWLAND RICE FIELDS IN NORTHEAST THAILAND

The diets and feeding of Oreochromis niloticus and Cyprinus carpio raised in two lowland rice fields in northeast Thailand were examined by analysis of stomach contents a niloticus fed primarily on detrital aggregate (DA). Plant material was the second most heavily consumed food and varied in its dietary contribution between fish and two study fields. The animal component of the diet was negligible in volume. The diet of fish from one rice field (site 1 ) changed from plants to DA over the season, while DA was the most consumed food in the other study field (site 2) throughout the season. Chlorophytes were the dominant algal group in rice fields. The low abundance of cyanophytes may have led to the dietary reliance on DA and plants. Although C carpio showed an overwhelming reliance on detrital aggregate throughout the season, there was a distinct but small dietary prey component which consisted mainly of chironomids and corixids. Seeds of grassy weeds (Gramineae) were also common in the diet. Fish from site 1 consumed cyclopoids, the cladoceran Chydorus, and the conchostracan Cyclesteria hislopi in the first half of the season, while corixids, chironomids, C hislopi, and seeds constituted a greater proportion of the diet in the latter part. In site 2, C carpio fed mostly on chironomids and corixids, throughout the season. The relatively low abundance of chironomids and microcrustaceans in the fields seems to have contributed to detrital aggregate being overwhelmingly the food of C carpio. C carpio foreguts were less full during the season compared with O. niloticus. Both fish species exhibited similar patterns of growth in both study fields. The condition factor of C carpio was similar in both rice fields. O. niloticus from both fields had very similar condition factors although the seasonal pattern of values varied somewhat.