The study was conducted Thoi Hung commune, Co Do district, Can Tho city. The objective of the study was studying effects of quinalphos insecticide on changes of cholinesterase activity and growth performances of common carp Cyprinus carpio cultured in rice-field.

Experiment was designed two concentrations: control (no quinalphos) and recommended dose (based on the producer); quinalphos insecticide was applied twice a during the experiment. Each plot of 1.000 m² approximately, three replicates, 2 fish/m² (weight of 5-8 g). OM 4218 variety was used in this experiment. Experimental time was 132 days. Fish were collected at day 0 (before application); day 1, day 7 and day 14 after the first and second exposing time.  Brain, muscle, gill and liver were collected to measure ChE activity. Growth parameters of common carp were mesured including in weight gain, day weight gain, specific growth rate. Survival and fish yield were determined after harvest. Rice yield and economics efficience of rice-fish system were also recorded during the experiment.

The results showed that at day 1 of the first and second exposing time, brain, muscle, gill and liver ChE activities were considerably inhibited 71-85%, 74-91%, 69-86% and 61-79% as compared to the control, respectively (p0.05). Total income and cost of rice-fish system in the control were significantly higher as compared to the recommended dose. These systems were no profit because of using commercial feed in experimental time.