Fish husbandry and rice culture management factors influencing the yield of introduced fish in ricefields of the Vietnamese Mekong Delta were studied by multiple regression analysis, A significant (P < 0.001) regression model was computed in which feed input and duration of culture period positively, and ricefield area, rice seeding rate and the year of the survey negatively affected the yield of introduced, as well as indigenous, fish. The negative impact of larger ricefields is probably the result of the escape of fish. This is also probably the reason for the year of survey since the average yield of introduced fish was 92.5 kg hal in 1995 (because of an extreme flood) as compared to 164.8 kg ha(-1) in 1994. A high seeding rate of rice results in a dense stand which suppresses the growth of fish. Opportunities for improvement of fish production are proper ricefield construction, reduced seeding rates, stocking fingerlings early in the dry season and more intensive feeding.