Abstract
This study investigates how fish are affected by the insecticide Padan 95SP (95% cartap hydrochloride, CH) used by rice farmers in the Mekong Delta, Vietnam. The impact on survival rate, acetylcholinesterase (AChE), total red (RBC) and white blood cells (WBC), blood glucose and lysozyme activity were measured in silver barb (Barbodes gonionotus), raised in a rice field. The field experiment included a control and two treatments, 0.7 kg (R) and 1.4 kg (2 R), of Padan 95SP/ha. Each treatment had three replicates. The water concentration of Padan 95SP decreased from 38.70 and 24.27 to 2.57 and 1.47 µg/L during the first seven days after exposure in the R and 2 R treatments respectively. Although causing only a few fish mortalities, the spraying of Padan 95SP caused significant physiological and immune responses in silver barb. The strongest AChE inhibitions of 18% and 34% were reached after one day in fish from the R and 2 R treatment respectively. The fish recovered fully after seven days. After an initial small increase during the first day, the RBCs, WBCs, and lysozyme activity decreased and were significantly lower in the treatments than in the control between day three and seven, but reached normal levels after 14 days. The glucose levels increased significantly during the first three days but decreased to the same levels as the control after seven days. Despite only few fish mortalities, the results suggests that the use of Padan 95SP has a negative effect on the long-term production of healthy fish in the Mekong Delta.