Background. This study raises awareness to the use of toxic pesticides and reiterates the well-known danger of these pesticides. The acute toxicity of two pesticides, dichlorvos and lindane against the African air-breathing catfish, Heterobranchus longifilis fingerlings was investigated under static bioassay in the laboratory. Relevant patents relating to acute toxicity of pesticides against fish were reviewed. Invention concerning the detection of biomarkers in material from a living organism relates to a method of testing whether a living organism has been exposed to stress, such as pesticide exposure.
Methods. Range finding bioassays were conducted to get the range of concentrations for the definitive bioassays. The range of concentrations of test media for dichlorvos was 0.2 - 1.5 mg l-1 while that of lindane was 35 - 80 mg l-1. The median lethal concentrations were determined using probit analysis.
Results. The test pesticides were found to be differentially toxic to the test species. The 96h LC50 values of 0.8187 and 41.566 mg l-1 for dichlorvos and lindane respectively indicated that dichlorvos was highly toxic while lindane was slightly toxic to the test species. Computed toxicity factor showed that dichlorvos was 50.8 times more toxic than lindane. The unpaired t-test showed that dichlorvos was significantly (p < 0.05) more toxic than lindane. The physical and chemical parameters data showed that over the 96h periods, the test pesticides caused slight increase in temperature, dissolved oxygen and ammonia of the test media, when compared with the untreated control. But they differentially altered pH, conductivity and alkalinity.
Conclusion. Since H. longifilis is sensitive to the test pesticides, it can therefore be considered as a good test species for the determination of acute toxicity and poisoning resulting from the pesticides and possibly for other compounds with similar intrinsic characteristics.
Keywords: Pesticides, dichlorvos, lindane, acute toxicity, Heterobranchus longifilis