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
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.