Study on fish mortality caused by the combined effects of pesticides and changes in environmental conditions

An accident killing many fish occurred in a drainage canal on reclaimed land. More than 10 000 mullet were killed in the accident. Newspapers reported that a decrease in salinity, caused by gate repairs, and a lack of oxygen, caused by rapid increase in the temperature, were the causes of the accident. In addition, our investigation discovered the possibility of pesticide inflow. The effects of these factors were estimated through experiments using mullet. A Shallow Sea Ecological Model (SSEM) was used to simulate the pesticide inflow and salinity change. The SSEM is based on the Object-Oriented Programming concept and it was very easy to extend the SSEM for modelling this accident. The extended SSEM revealed that the combined effects of water quantity, the decrease of salinity and the pesticide inflow caused the accident. The SSEM predicted that by decreasing the amount of pesticide down to one fifth of the actual level, the accident might not have occurred.