BackgroundThe present study compared lethal concentrations (LC50-96 h) of CdCl2, CrCl3, and Pb (NO3)2 between two scaled and scaleless freshwater fish species: Cyprinus carpio (Cyprinidae) and Pangasius hypophthalmus (Pangasiidae).MethodsThe experimental fishes were obtained from fish markets/ponds with average lengths and weights of approximately 11.68 ±1.92 and 9.8±1.9 cm, and 25.92±6.3 and 18.61±3.22 g for C. carpio and P. hypophthalmus, respectively. The fishes were exposed to different concentrations of cadmium (Cd) (0, 10, 20, 40, 80, 100, 120, 200 mg L-1) lead (Pb) (0, 20, 40, 50, 60, 90, 150 mg L-1), and chromium (Cr) (0, 5, 10, 20, 30, 40 mg L-1) for 96 h. Physicochemical parameters, such as dissolved oxygen, pH, and temperature of aquaria as well as mortality rate of the fishes, were monitored daily. ResultsThe 50% lethal concentrations (LC50-96 h) of CdCl2, CrCl3, and Pb (NO3)2 for P. hypophthalmus were found at 64.89, 7.46, and 48.06 mg L-1, and those of CdCl2, CrCl3, Pb (NO3)2 for C. carpio were detected at 84.8, 17.05, and 77.33 mg L-1. The ratios of heavy metal toxicity factors (TF) were greater for common carp compared to those for the catfish. ConclusionOur preliminary findings suggest that common carp C. carpio with higher LC50 (and LC100) values appears to be more tolerant to heavy metals exposure than the catfish (P. hypophthalmus). This may be due to the resistance to the heavy metals through protection from the carp's scaled body versus scaleless body of the catfish.