Responses of laboratory exposed catfish (Clarias gariepinus) to environmentally relevant concentrations of p,p′-DDT

Abstract

Technical grade DDT is annually sprayed for malaria control in many under developed countries world wide. Despite the controversy surrounding the use of DDT, minimal research concerning the effects on indigenous fish species in these areas has been conducted. In this study, the objectives were to identify some of the effects of sprayed p,p′-DDT on the common African sharptooth catfish species (Clarias gariepinus) under laboratory conditions. The effects were assessed by exposing specimens to three environmentally relevant concentrations of p,p′-DDT (0.66, 1.36 and 2.72μg/l) for 21 days and analysing a suite of biomarkers in the plasma, gonads and body morphometrics. The biomarkers were specifically selected based on their practicality in developing countries, which could potentially be utilised for continued monitoring, and included alkali-labile phosphate (ALP), calcium, magnesium and zinc as the indirect measures of vitellogenin, gonadosomatic index, gonad mass manipulated using analysis of covariance, and condition factor. The results showed no significant (p<0.05) dose-dependent changes in the plasma, gonads and body condition of C. gariepinus, indicating that these species were not responsive to the p,p′-DDT concentrations when exposed sub-chronically. This lack of a response suggested that mature C. gariepinus are tolerant to 21 days exposure of low levels of p,p′-DDT.