Barbodes gonionotus (Bleeker) is a popular fish species in rice-fish culture. In Vietnam's Mekong Delta, the species is often grown in polyculture with Oreochromis niloticus (L.) and Cyprinus carpio L. In this study, we used the data of eight experiments into such polycultures at the Co Do rice-fish experimental station to look whether the rice stage or fish biomass had any effect on the specific growth rate (SGR) of B. gonionotus. The B. gonionotus net production figures varied from 1.7 to 547.7 kg/ha, while the SGR varied from 0.27% to 3.58% body weight/day. We found that SGR values did not depend on the developmental stage of the rice crop. However, the SGR values significantly decreased with increasing standing biomass (SB) of B. gonionotus, O. niloticus or wild fish. We concluded that intraspecific and interspecific competition is an important issue in B. gonionotus culture in rice fields. Besides this, SGR values were higher in the wet season and in plots with inorganic fertilizer or pig manure application. (C) 2002 Elsevier Science B.V. All rights reserved.