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Mesocosm Studies on the Effect of Propanil on the Water Quality and Plankton Communities of Four Aquaculture Pond Systems

Peter Perschbacher and Regina Edziyie

A study was conducted to evaluate propanil effects on water quality and plankton of four different aquaculture systems: penaeid shrimp, goldfish, hybrid striped bass, and channel catfish. Propanil or Stam is a common rice herbicide, which has impacted adjacent channel catfish ponds by reducing phytoplankton. The experimental design utilized 500-L outdoor mesocosms filled in triplicate with water from the four systems in four trials. After filling from nearby pond systems, propanil was added at 0.2 times the full rice field application rate, which was judged to be a potential drift or runoff level. This was equivalent to 0.1 mg/L. Beginning 24 h after application, morning water column samples were taken daily until the treatments returned to normal as indicated by no differences from the controls. Ten parameters were measured. Although results indicated short-term impacts, dissolved oxygen and zooplankton levels (for fry ponds) were reduced to potentially harmful levels. In addition, impacts depended on the phytoplankton levels, as indicated by chlorophyll a. Low levels (shrimp ponds), and high levels (goldfish ponds) were least affected. Greatest impacts were in the mid-range of approximately 200 ug/L (channel catfish). Farmers should monitor oxygen levels and zooplankton in fry ponds if propanil contamination is suspected.