Comparison of the acute toxicity and behavioural effects of two pyrethroids on African catfish Clarias gariepinus fingerlings

Abstract

Two of the most-commonly used pyrethroid insecticides were subjected to static bioassays to determine their acute toxicity to Clarias  gariepinus fingerlings, followed by comparisons of their impact on mortality and behavioural changes in the fish. The LC₅₀ values for  deltamethrin (DMT) at exposure durations of 24, 48 and 96 h were 12, 9 and 8 µg l⁻¹, respectively; the LC₅₀ values for cypermethrin (CYP)  at the same exposure durations were 55, 44 and 26 µg l⁻¹, respectively. The estimated safe limits ranged from 8×10⁻¹ to 8×10⁻⁵ µg l⁻¹  for DMT, and 26×10⁻¹ to 26×10⁻⁵ µg l^-1 for CYP. The tested substances had an acute toxicity effect on fish development as they caused  death, and chronic toxicity effects as they changed fish behaviour. Fish exposed to either one of these pesticides showed behavioural  alterations, such as loss of static balance, excessive mucous secretion, irregular swimming, gulping of air and skin discolouration. The  results reveal that CYP was less toxic (96-h LC₅₀ = 26 µg l⁻¹) than DMT (96-h LC₅₀ = 8 µg l⁻¹) based on the greater LC₅₀ value and a lower  percentage of mortality. To avoid potential ecotoxicological risks to aquatic life, use of these pyrethroids in both terrestrial and  freshwater ecosystems must be treated with caution.