This International Standard specifies a method for the determination of the long-term sublethal toxicity of substances soluble in water under specified conditions to a species of anadromous fish [ Oncorhynchus mykiss Walbaum (Teleostei, Salmonidae) - common name, rainbow trout] in fresh water. NOTE 1 “Substances” is considered to include pure chemicals tested singly or in mixtures, waste waters, process waters or other waters whose sublethal toxicity to fish it is necessary to determine. A range of concentrations of waste and process waters should be tested (see 8.2). The response measured is the Change in rate of growth of fish exposed to the test substance over periods of 14 d and 28 d (see [I] in annex B). NOTE 2 The mass of each fish at the Start of the test, the period of exposure, the feeding regime and temperature range have been Chosen to ensure that the control fish will be growing exponentially throughout the test. The method is applicable for assigning, for each test substance, a category of prolonged sublethal toxicity to Oncorhynchus mykiss under the test conditions. The results are insufficient by themselves to define water quality limits for environmental protection. lt is possible for the method to be adapted for use with other freshwater fish and marine and brackish water fish with appropriate modification of the test conditions, particularly with respect to the tempera