ABSTRACT
Species to be used in toxicity tests are obtained from two principal sources. Toxicity may be affected by the action of such factors upon the chemical speciation of the toxicant and hence its availability and also by their action upon the test organism and so its response to the toxicant. Through-flow systems greatly improve the constancy of toxicant concentrations and other conditions within test vessels and, where desirable, facilitate a higher concentration of test organisms. Traditionally, fish have been the principal group used in aquatic toxicology. Several freshwater triclads can be maintained without difficulty in the laboratory and although toxicity tests with triclads were carried out as long ago as 1937 by Jones, the group does not play a major role in aquatic toxicology. Tests may be of very simple design and, therefore, cheap and easily replicated or on the other hand, very complex, allowing precise control of experimental factors and simulation of environmental conditions.
