Author(s): Aysha Siddiqa, Md. Jahidul Islam, Md. Shazadur Rahman, MN Uddin and Rubeca Fancy

Abstract: Pesticide is a major factor for fish mortality along with water temperatures. Six fish species namely Climbing perch (Anabas testudineus), spotted snakehead (Channa punctatus), Thai shorputi (Barbodes gonionotus), Indian torrent catfish (Amblyceps mangois), pool barb (Puntius sophore) and tangra (Batasio tengana) were exposed to various concentrations of Confidor 70WG to assess the lethal concentrations (LC₅₀). For 96 hours of exposure, the median lethal concentration (LC₅₀) values of Confidor 70WG on these five species were 46.49, 40.80, 35.32, 49.25, 27.61 and 44.51 ppm, respectively. Mortality rate and behavioral changes of fish at different concentrations were determined. Some physicochemical parameters of water such as temperature, pH, dissolved oxygen, total dissolved solids and electrical conductivity were also measured and compared with the aquaculture water quality standard. Temperature remained within the range of 25-30 °C and the pH of water was 6.6-7.0 in presence of pesticide. Physiological responses like rapid opercular movement, hyper secretion of mucus and frequent gulping of air was observed during the initial stages of exposure after which it became occasional. By the cause of Confidor 70WG, the pectoral fins of the fishes were reversed. In stress, the unusual behavior of experimental fishes may be due to obstructed functions of neurotransmitters.

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