###### Abstract  
Over the past twenty years, the prescription of antidepressant drugs has increased all over the world. After their application, antidepressants, like other pharmaceuticals, are excreted and enter the aquatic environment. They are dispersed among surface waters mainly through waste water sources, typically at very low concentrations-- from a tenth up to hundreds of ng/L. Frequently detected antidepressants include fluoxetine and citalopram--both selective serotonin reuptake inhibitors. The aim of our study was to assess the embryotoxicity of fluoxetine hydrochloride and citalopram hydrochloride on the early life stages of zebrafish (_Danio rerio_) and the African clawed frog (_Xenopus laevis_). The embryos were exposed to various concentrations of the individual antidepressantsants and of their mixtures for 96 h. The tested levels included both environmentally relevant and higher concentrations for the evaluation of dose-dependent effects. Our study demonstrated that even environmentally relevant concentrations of these psychiatric drugs influenced zebrafish embryos, which was proven by a significant increase (\(p<0.01\)) in the embryos' heart rates after fluoxetine hydrochloride exposure and in their hatching rate after exposure to a combination of both antidepressants, and thus revealed a potential risk to aquatic life. Despite these results, we can conclude that the African clawed frog is more sensitive, since exposure to the highest concentrations of fluoxetine hydrochloride (10,000 ug/L) and citalopram hydrochloride (100,000 ug/L) resulted in total mortality of the frog embryos. s 2021 20  
Antidepressants represent an important group of drugs that is widely used in the treatment of various mental disorders (e.g., depression, bipolar disorder, schizophrenia, other psychoses, chronic pain, autism, insomnia, anorexia). The main function of antidepressants is to create a neurohumoral balance by influencing the activity of neurotransmitters [12; 14; 19]. According to the mechanism of action, they can be divided into several groups. Tricyclic antidepressants, so-called first-generation antidepressants, are among the oldest types of drugs used in the treatment of depression that act as a blocker of the reuptake of one or more neurotransmitters. Unfortunately, they have more adverse effects compared to other groups. The most important representatives of this group are, for example, nortriptyline, amitriptyline, and clomipramine. Another group of antidepressants is selective serotonin reuptake inhibitors (SSRIs), which are among the most commonly prescribed antidepressants. The most important representatives are fluoxetine, serntraline, citalopram, and others. Other frequently prescribed types of antidepressants are serotonin and norepinephrine reuptake inhibitors (e.g., venlafaxine), which are used for the treatment of major depression, anxiety, mood disorders, etc. Compared to the other groups, they have milder side effects. Another type are antidepressants that act as reversible inhibitors of monoamine oxidases (e.g., moclobemide) [14; 15; 20; 21]. Recently, the presence of antidepressants in fresh and marine ecosystems has increased. Therefore, it potentially poses a significant ecological risk to various non-target aquatic organisms [22; 23; 24; 25; 26; 27]. Antidepressants are detected in surface waters at concentrations most often ranging in orders of magnitude from a tenth to hundreds of ng/L [14]. Higher concentrations are detected especially downstream of hospitals or in wastewater treatment plants [28; 29]. Although the detected levels of these medications are relatively low, it is known that even such environmentally relevant doses can disturb the physiological functions of exposed aquatic organisms [14]. Ecotoxicological studies confirm a number of negative effects on various aquatic organisms, such as the induction of oxidative stress [25; 30], embryotoxicity [31], immunotoxicity [32], developmental abnormalities [33; 34; 35], histopathological findings [32; 34], etc.