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 rai sed in two lowland rice fields in northeast Thailand were examined by analysis of stomach contents a niloticus fed primarily on detrital agg regate (DA). Plant material was the second most heavily consumed food and varied in its dietary contribution between fish and two study fiel ds. The animal component of the diet was negligible in volume. The die t 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 fi eld (site 2) throughout the season. Chlorophytes were the dominant alg al 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, th ere was a distinct but small dietary prey component which consisted ma inly of chironomids and corixids. Seeds of grassy weeds (Gramineae) we re 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, throughou t the season. The relatively low abundance of chironomids and microcru staceans in the fields seems to have contributed to detrital aggregate being overwhelmingly the food of C carpio. C carpio foreguts were les s full during the season compared with O. niloticus. Both fish species exhibited similar patterns of growth in both study fields. The condit ion factor of C carpio was similar in both rice fields. O. niloticus f rom both fields had very similar condition factors although the season al pattern of values varied somewhat.