## 4 Comparison of Toxicity in Adult Fish and Embryo Assay  
Previous research has tried to validate the fish embryo test as an alternative test method to adult fish tests [56; 57; 58; 59; 60; 61; 62; 63; 64; 65]. Based on zebrafish toxicity assays, various chemical species were exposed to fish embryos, and their resultant toxicity values were compared with those for adult fish tests and compared to those for other fish species; this research was applied to reduce the unnecessary sacrifice of adult fish by animal testing. To evaluate the applicability of the FET (fish embryo test) in chemical toxicity testing, [PERSON] et al. [56] compared and analyzed the fish and embryo toxicity data for 143 chemicals and identified the toxicity correlation for overall chemicals between adult fish and fish embryos. The lethal and sub-lethal endpoints were also observed during the chemical exposure. Compared to zebrafish embryo toxicity, all the fish embryo data, including _P. promelas, O. latiges_, and _C. gariepinus_, showed similar toxicity trends; this proximity confirmed that the zebrafish embryo toxicity data can be considered as representative of toxicity for chemical exposure among various fish species, except for high-molecular-weight surfactants. Furthermore, the adult fish assay has similar toxicity trends derived via FET, so FET can be a suitable alternative for adult fish test. [PERSON] et al. [57] proposed the FET as an alternative tool for adult fish assays by comparing the toxicity data of chemical species. The toxicity value of the FET showed  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Substance**} & \multicolumn{2}{c}{**US EPA [53]**} & \multicolumn{2}{c}{**Canada [54]**} & \multicolumn{2}{c}{**ECHA [55]**} \\ \cline{2-7}  & \multicolumn{2}{c}{**Freshwater**} & \multicolumn{2}{c}{**Freshwater**} & \multicolumn{2}{c}{**Emission Medium**} \\ \cline{2-7}  & **Short-Term** & **Long-Term** & **Short-Term** & **Long-Term** & **Inland Surface** & **Surface Water * \\ \hline Heptachlor & 0.52 & 0.0038 & — & 0.01 & 0.0003 & 0 \\ \hline Iron & — & 1000 & — & 300 & 0 & 0 \\ \hline Lead & 65 & 2.5 & — & — & 14 & 14 \\ \hline Malathion & — & 0.1 & — & — & — & — \\ \hline Mercury & 1.4 & 0.77 & — & 0.026 & 0.07 & 0.07 \\ \hline Methoxychlor & — & 0.03 & — & — & — & — \\ \hline Mirex & — & 0.001 & — & — & — & — \\ \hline Nickel & 470 & 52 & — & — & 34 & 34 \\ \hline Nonylphenol & 28 & 6.6 & — & 1 & 2 & 2 \\ \hline Parathion & 0.065 & 0.013 & — & — & — & — \\ \hline Pentachlorophenol & 19 & 15 & — & 0.5 & 1 & 1 \\ \hline PFOS & 71 & 0.25 & — & — & 36 & 7.2 \\ \hline PFOA & 3100 & 100 & — & — & — & — \\ \hline PCBs & — & 0.014 & — & 0.001 & — & — \\ \hline Selenium & — & — & — & 1 & — & — \\ \hline Silver & 3.2 & — & — & 0.25 & — & — \\ \hline Sulfide- & \multirow{2}{*}{—} & \multirow{2}{*}{—} & \multirow{2}{*}{—} & \multirow{2}{*}{—} & \multirow{2}{*}{—} & \multirow{2}{*}{—} \\ Hydrogen & & & & & & \\ \cline{1-1  
similar sensitivity to those of fish adult tests, except for permethrin and allyl alcohol. [PERSON] et al. [58] also compared the fish toxicity data of chemical groups in fish embryos and adults and found that large functional groups of chemicals such as industrial organic compounds, pesticides, and surfactants showed similar toxicity trends, and these trends were also confirmed upon interspecies comparison. Unfortunately, some neurotoxic compounds (aldicarb, azinphos methyl, cyanizine, dieldrin, diquat dibromide, endosulfan, esfenvalerate, and picloram) have low embryonic toxicity in fish compared to adult fish toxicity [59; 60]. The toxic impacts of movement in larval fish corresponded to lethality in adult fish, and the neurotoxic impacts can be predicted by determining the motility of larval fish [60]. These observations suggest that the fish toxicity data for organic compounds or non-ionic chemicals could contain uncertainties for extrapolation to ionic chemicals or inorganic compounds of different chemical functional groups.