Aquaculture Crsp 21st Annual Technical Report

This study was conducted in cage aquaculture villages in Hongngu District, Dong Thap Province of Vietnam during November 2001 to November 2002. Cage culture areas are located in the confluence of So Thuong Canal and one branch of the Mekong River. The purposes of this study were to investigate the cage culture system and its related environmental conditions, to determine the quality and quantity of pollutants produced by cages, to detect the fate of pollutants in the river, and to recommend methods for pollution mitigation in cage culture. Ninety-five cage farmers were randomly selected for interviews, using a survey to investigate socioeconomic characteristics of farmers, cage culture practices, investment cost and return, problems, and other information. These farmers managed 156 cages out of a total of 204 cages in the study area. The survey consisted of a structured checklist and open-ended questions. The cage culture area was divided into three equal sections (upstream, middle stream, and downstream) in both the So Thuong Canal and the Mekong River. Nine cages—one from each section of the So Thuong Canal and two from each section of the Mekong River—were randomly selected from each section for measurement of water quality and determination of nutrients in fish, feed, and sediments. The socioeconomic survey showed that the major species cultured in cages are Pangasius spp. catfish in either monoculture or polyculture with P. hypothalamus, P. bocourti, P. conchophilus, or red tail barb (Barbodes altus). Almost all farmers used homemade feed prepared with locally available ingredients, and the homemade feed accounted for about 98% of the total feed input. More than 50% of farmers produced negative net economic returns, and most cage farmers listed lack of capital, unstable costs, and unstable fish prices as the top three constraints for cage culture. Water quality measurements in the present study showed that there were no significant differences in all water quality parameters among cages in different locations (upstream, middle stream, and downstream), between cage water and open water, or between the water in front of and downstream from the cage culture areas. Waste loadings from cage culture do not appear to have significant impact on fish production and water quality.