A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Aquacu lture and aquatic resources management, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 2008

Farmer{u2019}s survey and long term toxicity test were carried out at Can Tho city in 2007 to evaluate the current pestic ides use and its effects on structure and population of zooplankton and benthic invertebrate as well as the survival rate and yield of wild and farmed rice fish systems. 54% of total 40 pesticides us ed in the region were inse cticides followed by fungicide (34%) and herbicide (12%).The most common insecticides were fenobucarb and alpha- cypermethrin. The yield of farmed fish of IPM rice fish farmers was significantly higher than non-IPM rice fish farmers. As produc er recommended, the dose of 0.45mg a.i./L fenobucarb and 15.2 og a.i./L alpha -cypermethrin did not affect on the survival rate but significant reduced yield for common carp (P <0.05). The survival rate and yield of common carp were significantly reduced at th e farmer dose of 1.35mg a.i./L fenobucarb and 25.8 og a.i./L alpha-cypermethrin (P< 0.05). The population dens ity of zooplankton and benthic invertebrate were not affected at the dose of 1.35mg a.i./L fenobucarb. The population densities of benthic i nvertebrate were significantly reduced at the both doses of 15.2 and 25.8 og a.i./L alpha-cypermethrin. Th e population density of zooplankton was not affected at the dose of 15.2 og a.i./L alpha -cypermethrin, but it wa s significantly reduced at the dose of 25.8 og a.i./L. It indicates th at the doses of insec ticides recommended by manufacture were safe for environment and aq uatic wildlife. Meanwhile, the doses applied by farmers highly affected on the structure and population density of zooplankton and benthic invertebrate, the survival rate and yield of stocked fish in rice and rice fish system.