Acute toxicity of an organophosphate, dimethoate to an air breathing fish, Colisa fasciatus (Bl. & Schn.)

Acute toxicity bioassay was carried out in a static renewal system to assess the toxicity of dimethoate to Colisa fasciatus. Mortality was recorded at 24, 48, 72 and 96 hr exposure and data was analyzed by US EPA software version 1.5 based on probit methods to calculate LC₅₀ values and 95% lower and upper confidence limits. LC₅₀ values of dimethoate for 24, 48, 72 and 96 hr were found to be 22.15 mg/L, 21.99 mg/L, 21.74 mg/L and 21.65 mg/L, respectively. Behavioral alterations such as decreased opercular movement, surfacing, abnormal swimming, increased mucus secretion and loss of balance were also observed in the exposed fishes.