Studies on the Toxicity of a few Pesticides on Colisa fasciatus and Notopterus notopterus with Reference to Histopathology and Histochemistry. Part 1: Bioassay Studies

An attempt has been made to study the toxicity of two commonly used pesticides aldrin (organochlorine) and ethyl-parathion (organophosphorus) to the fish Colisa fasciatus (Anabantidae) and Notopterus notopterus (Notopteridae). During bioassay studies, the behaviour of the fishes was recorded. The aldrin concentration used lies between 0.021 mg/1 and 0.042 mg/1 for C. fasciatus and 0.00056 mg/1 and 0.00135 mg/1 for N. notopterus. The ethyl-parathion concentration used lies between 1.8 mg/1 and 3.7 mg/1 for C. fasciatus and 0.49 mg/1 and 1.00 mg/1 for N. notopterus.

• – The effect of lethal aqueous concentrations of pesticides on the Fishes prior to death are usually manifested by excitation, erratic swimming ability, difficulty in respiration, increasing in ventilation rate, jerky movements of body and fin fast, up- and downward movements, convulsions, loss of equilibrium, loss of the original colour of the body skin and the excess secretion of mucus by the gills and the body wall.
• – the TL_m values for 24, 48 and 96 hours of exposition are determined for both species of fish and both pesticides at the following variables:

• ? three levels of temperature,
• ? three levels of dissolved oxygen,
• ? three levels of pH,
• ? three fish sizes.

• – statistical analysis of variance shows, that all variables have a significant effect on the TL_m values of both pesticides for both fish species;
• – Aldrin (chlorinated hydrocarbon) is more toxic than ethylparathion (organophosphate) at all variables;
• – Colisa fasciatus is the more resistant species than Notopterus notopterus.
• – the relationship between the total number of the fishes N₀, survival numbers N and time t can be expressed by a mathematical formula as:
• – the harmless concentration to C. fasciatus ranged from 0.0049 mg/1 to 0.0161 for aldrin, 0.54 mg/1 to 0.99 mg/1 for ethyl-parathion and to N. notopterus from 0.00012 mg/1 to 0.00045 mg/1 for aldrin, 0.10 mg/1 to 0.21 mg/1 for ethyl-parathion;
• – the aldrin should be diluted at least 4000 times and ethyl-parathion 320 times of its actual concentration.