## 3 Derivation of Water Quality Criteria and Relevant Fish Assay
### Comparison of Acute and Chronic Toxicity for Fish and Priority Substances in WQS  
Based on the guidelines for deriving the WQS to protect aquatic eco-receptors, each organization presented different standards for classifying the acute and chronic toxicity in fish (Table 5). While most fish test guidelines follow a 4-day acute exposure without developmental distinction [1; 2; 3; 4; 5], Canada, Australia, and New Zealand clearly distinguish the exposure period by developmental stage, with common criteria of 7 days for fish embryos and larvae and 21 days for juvenile and adult fish [2; 5]. The fish species used in toxicity assays have rapid growth rates, so different developmental stages have different sensitivities to toxicants and pollutants [1; 2; 4]. These aspects eventually confirm the application of the appropriate exposure period at each developmental stage of the fish. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Acute/Chronic** & \begin{tabular}{c} **Test** \\ **Guideline** \\ \end{tabular}  & \begin{tabular}{c} **Test Species** \\ **Test Species** \\ \end{tabular}  & \begin{tabular}{c} **Exposure** \\ **Stage** \\ \end{tabular}  & \begin{tabular}{c} **Test** \\ **Duration** \\ \end{tabular}  & \begin{tabular}{c} **Endpoints** \\ \end{tabular}  \\ \hline Acute & \begin{tabular}{c} Freshwater fish \\ acute toxicity \\ test [16] \\ \end{tabular}  & \begin{tabular}{c} _Cyrrinus carpio, Oryzias latipes,_ \\ _Misgurnus anguillicandatus_ \\ \end{tabular}  & Adult & 4 days & \begin{tabular}{c} Mortality, abnormality, \\ growth (length/weight) \\ \end{tabular}  \\ \hline Acute & \begin{tabular}{c} Freshwater fish \\ effect test [16] \\ \end{tabular}  & \begin{tabular}{c} _Cyrrinus carpio, Oryzias latipes,_ \\ _Misgurnus anguillicandatus_ \\ \end{tabular}  & Adult & 4 days & \begin{tabular}{c} Mortality, abnormality, \\ growth (length/weight) \\ \end{tabular}  \\ \hline Fish acute toxicity & \begin{tabular}{c} Fish acute toxicity \\ test [51] \\ \end{tabular}  & \begin{tabular}{c} _Cyrrinus carpio, Oryzias latipes,_ \\ _Pocella reticulata, Danio rerio,_ \\ _Leponis macrochirus,_ \\ _Oncorhynchus mykiss_ \\ \end{tabular}  & Embryo & 4 days & Mortality, abnormality \\ \hline Fish early life stage & \ \begin{tabular}{c} Fish acute toxicity \\ test [16] \\ \end{tabular}  &
\begin{tabular}{c} _Oryzias latipes_ \\ _Oryzias latipes,_ \\ _O  
Fish are vertebrates, and fish tests using juveniles or adults can be unethical assessments for animal testing [4; 6; 7; 8]; these should be replaced by alternative test methods using fish embryos or larvae. Furthermore, fish embryo- and larval-stage organisms are not considered to be regulated by the ethics of animal testing [6; 7; 8], so fish embryo assays are comparatively utilized in toxicity assessment. According to the well-organized distinction between acute and chronic toxicity to fish based on the developmental stages [2; 4], the 7-day exposure in the fish embryo or larval test can be regarded as a discriminative baseline for chemical toxicity in early developmental stages of fish. Fish assays using embryos or larvae for less than 7 d are considered for acute toxicity testing. For the estimation of chronic toxicity, fish embryos or larvae should be exposed for at least 7 d, depending on the developmental stage. As suggested in the guidelines of each country and organization, chronic toxicity tests are recommended, so the early-stage or developmental-stage fish assay could be used as alternative tools to derive toxicity data for chemicals or toxicants for WQS. The EQS for waterbodies (WQS) considers various indicators, including the acute and chronic toxicity of aquatic eco-receptors, and physico-chemical and microbiological indicators. There are different regulations applied to derive the WQS in each country or organization, with multiple indicators considering the impacts on the aquatic organisms caused by the characteristics of specific substances.