Fish Acute Toxicity (OECD 203)
Freshwater Fish, Acute Toxicity Test (OECD 203, JMAFF, EC C1)
Species specified for Japanese MAFF regulations
The preferred freshwater species are rainbow trout (Oncorhynchus mykiss) or carp (Cyprinus carpio).
Fish are introduced into glass aquaria containing water to which the test substance has been added at known concentrations. Fish are observed for mortality and sub-lethal symptoms at specified periods of time. The results of the test are expressed in the form of LC50 values (that is the concentration causing 50% mortality among the test population).
The duration of exposure is normally 96 hours. The maximum concentration at which no mortality occurs (NOEC) and the minimum concentration at which 100% mortality occurs are also reported together with observations of toxic symptoms. The slope of the dose/response curve is provided wherever possible. This provides useful extra information for use in environmental risk assessment or hazard classification of the test substance.
In order to reduce the numbers of fish tested, but still informing the hazard-assessment process, the fish test is now commonly conducted as a limit test with a single concentration tested. The lowest concentration causing effects in studies previously conducted with algae and invertebrates is used to demonstrate the LC50 for fish is below that concentration, therefore demonstrating that the fish is not the most sensitive of the organisms tested. Where mortalities are seen a full range of concentrations is tested to determine the LC50.