## 3 Results  
### Cumulative Mortality of Zebrafish and African Clawed Frog Embryos  
The results of the cumulative mortality of the zebrafish and African clawed frog embryos are presented in Tables 1 and 2. In the embryonic test on zebrafish, no significant differences were observed between the control and experimental groups exposed to fluoxetine hydrochloride and citalopram hydrochloride as single substances and their mixture at the same time of exposure (Table 1). No mortality was found in the control group during the embryotoxicity assay. The highest cumulative mortality (8.3%) was found in the experimental group exposed to fluoxetine hydrochloride at 100 ug/L at 72 hpf. The same mortality was also observed in the experimental group exposed to the medium concentration of both antidepressants (fluoxetine hydrochloride--10 ug/L, citalopram hydrochloride--1 ug/L). However, this cumulative mortality was already recorded at 24 hpf. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Group** & **Concentration** & **24 hpf** & **48 hpf** & **72 hpf** & **96 hpf** \\ \hline control & - & 0 & 0 & 0 & 0 \\ \hline  & 0.1 ug/L & 0 & 0 & 0 & 0 \\  & 1 ug/L & 0 & 0 & 0 & 0 \\ F & 10 ug/L & 5.6 & 5.6 & 5.6 & 5.6 \\  & 100 ug/L & 5.6 & 5.6 & 8.3 & 8.3 \\  & 1000 ug/L & 5.6 & 5.6 & 5.6 & 5.6 \\  & 1000 ug/L & 5.6 & 5.6 & 5.6 & 5.6 \\ \hline  & 0.01 ug/L & 0 & 0 & 0 & 2.8 \\  & 0.1 ug/L & 0 & 0 & 2.8 & 2.8 \\  & 1 ug/L & 0 & 0 & 0 & 0 \\ C & 10 ug/L & 2.8 & 2.8 & 2.8 & 2.8 \\  & 1000 ug/L & 0 & 0 & 0 & 0 \\  & 10,000 ug/L & 0 & 0 & 0 & 0 \\  & 100,000 ug/L & 5.6 & 5.6 & 5.6 & 5.6 \\ \hline  & low & 2.8 & 2.8 & 2.8 & 2.8 \\ F + C & medium & 8.3 & 8.3 & 8.3 & 8.3 \\  & high & 2.8 & 2.8 & 2.8 & 2.8 \\ \hline \end{tabular} Abbreviations: F—fluoxetine hydrochloride; C—tialopram hydrochloride; hpf—hours post-fertilization; low—fluoxetine hydrochloride 0.1 ug/L, citalopram hydrochloride 0.01 ug/L; medium—fluoxetine hydrochloride 100 ug/L, citalopram hydrochloride 1 ug/L, citalopram hydrochloride 100 ug/L, citalopram hydrochloride 100 ug/L, citalopram hydrochloride 100 ug/L.  
\end{table} 
Table 1: Cumulative mortality (%) of zebrafish embryos exposed to antidepressants as single substances and as a mixture. No significant differences (\(p>0.05\)) were observed between the control and the experimental groups at the same time of exposure. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Concentration** & **24 hpf** & **48 hpf** & **72 hpf** & **96 hpf** \\ \hline control & - & 0 & 0 & 0 & 5.6 \\ \hline  & 0.1 ug/L & 0 & 0 & 0 & 0 \\  & 1 ug/L & 0 & 0 & 0 & 5.6 \\ F & 100 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 5.6 & 5.6 \\  & 10,000 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 0 & 5.6 \\  & 1000 ug/L & 0 & 0 & 0 & 5.6 \\  & 100,000 ug/L & 0 & 0 & 0 & 5.6 \\  & 100,000 ug/L & 0 & 0 & 0 & 5.6 \\ \hline  & low & 0 & 0 & 5.6 & **44** \\ F + C & medium & 0 & 5.6 & 5.6 & 11.1 \\  & high & 0 & 0 & 0 & 5.6 \\ \hline \end{tabular} Abbreviations: F—fluoxetine hydrochloride; C—tialopram hydrochloride; hpf—hours post-fertilization; low—fluoxetine hydrochloride 0.1 ug/L, citalopram hydrochloride 0.01 ug/L; medium—fluoxetine hydrochloride 1000 ug/L, citalopram hydrochloride 100 ug/L.  
\end{table} 
Table 2: Cumulative mortality (%) of African clawed frog embryos exposed to antidepressants as single substances and as a mixture. Bold font and the asterisks indicate a significant difference (\({}^{\star}\)\(p<0.05\), \({}^{\star\star}\)\(p<0.01\)) between the control and the experimental groups at the same time of exposure. 5.6% at 96 hpf. A high toxic effect was found in the highest test concentrations of both antidepressants, fluoxetine hydrochloride (10,000 ug/L) and citalopram hydrochloride (100,000 ug/L), as single substances, where a 100% mortality was observed at 72 hpf. These results were significantly different to the cumulative mortality in the control group at the same time of exposure (\(p<0.01\)).