## 3 Derivation of Water Quality Criteria and Relevant Fish Assay
### Australia and New Zealand  
Australia and New Zealand published the freshwater and marine water quality guideline in 1992 and updated the content in 2000, and the current version has made some amendments regarding the technical rationale for deriving toxicity values in 2018 [4; 45; 46]. The WQS derivation for water quality in Australia and New Zealand covers the various taxonomies associated with trophic levels and nutrient cycling. Fish are a typical families of a realistic biological community, which consume some living organisms as a feeding activity. Furthermore, the ethical problem of animal experimentation has been an issue for fish assays, so relevant matters have been reviewed. Accordingly, the Commonwealth Scientific and Industrial Research Organisation (CRISO) modified the technical rationale for some detailed explanations for deriving the WQS value for toxicants in Australia and New Zealand [4; 46].  
Firstly, the definitions of acute and chronic toxicity were re-defined. In 2000, acute toxicity was defined as the rapid effects caused by substances in living organisms (for instance, death); continuous or prolonged exposures of test organisms for weeks to years on test organisms were considered as chronic toxicity [45]. Previously, chronic toxicity only included some biological responses of long duration with slow processes affecting one life-stage of living organisms [45]. The revised definition covered several common tests, including larval development tests, which had been classified as acute or chronic assays. Re-defined acute toxicity means lethal or sub-lethal effects occurring after a short exposure to chemicals; chronic toxicity has also been defined as lethal or sub-lethal effects for substantial portion of the lifetime of an organism (greater than 10% of the life span). Adverse effects on sensitive early-life-stage organisms have also been considered as chronic toxicity [4].  
Especially for fish toxicity, the classification of acute and chronic toxicity is determined by the initial stage of development at the time of exposure and test duration with various endpoints. In juvenile or adult fish, the effects of substances for durations of less than 3 weeks are considered as acute toxicity; impacts from a longer exposure period are considered to be chronic toxicity for fish. Accordingly, the 7-d toxicity test for juvenile or adult fish is regarded as an acute toxicity assessment. For early-stage fish, including embryos and larvae, the classification of the exposure duration is one week, with a test duration of less than 7-d being an acute effect; if the exposure duration is longer than 7 days, the effects are considered to be chronic toxicity.  
Considerable endpoints have been expanded in the revised guideline [46]; both traditional endpoints (survival growth and reproduction) and non-traditional endpoints, such as swimming ability and physiological or biological changes, can be used to assess the toxicity of organisms. Some endpoints related to fish embryos can be measured within a week, which is considered by experts to be acute or chronic toxicity, and the relevant basis for the decision should be documented.