The paper deals with the susceptibility of several species of small freshwater fish to toxicants, The results indicate that small freshwater fish is highly susceptible to metal and organic phosphorus pesticide and that small freshwater fish can be used as experimental animal for toxicity test. Clear symptoms such as tumefied kidney and crooked body can be observed by exposing gold fish (Carassius auratus ) to cadmium toxicity, therfore it is possible to use gold fish as an experimental animal for the study of environmental toxicology and oncoiogy.