Acute toxicity of cadmium to freshwater fishes and its relationship with body size and respiratory strategy.

Acute toxicity assays in freshwater fishes are used in diverse local and regional regulations. Lethality is a complex biological process, depending on both extrinsic and intrinsic factors. The extrinsic parameters (pH, temperature, hardness and alkalinity, among others) have been widely studied and their influence on toxicity has been well characterized. In contrast, less attention has been given to intrinsic parameters (body size, sex, life habits) and their influence on toxicological sensitivity is poorly known. This work is focused on the effect of intrinsic parameters on lethality. For this purpose, we systematically reviewed experimental studies that reported data on acute lethality (LC50-96 h) of cadmium to freshwater fishes. We studied the allometric relationship between reported body weight and lethality, and the influence of the respiratory strategy and adaptation to extremely low-ionic strength environments on the sensitivity of fishes to cadmium. We observed a strong relationship between LC50-96 h and body weight. The fish group adapted to low-ionic strength water (OF) showed the highest sensitivity to cadmium, with the allometric constants being a = 0.0045 and b = -1.11, while the group of air-breathing fishes such as Channa marulius and Hepteroneustes fossillis exhibited the lowest sensitivity, with the allometric constants being a = 42.04 and b = -0.44.The effect of the intrinsic parameters can be easily combined with known toxicological models, thus contributing to the construction of models suitable for a wider range of species.