Abstract. The effect of benzodiazepine anxiolytic diazepam in Danio rerio was investigated. Methods. A stress test on novelty situation was used: a fish was placed first in a beaker with a dissolved pharmacological substance (or water) and then into a novel tank for 6 min, where the trajectory, the path length, the number of movements to the upper part of the novel tank, the number and time of the pattern of freezing of the experiment were measured. Results. In response to the novelty of tank, the fish was shown to react by submerging to the bottom, increasing the freezing, and reducing the number of movements to the upper half of the novel tank. After diazepam exposure (administration), the fish was not only in the lower, but also in the upper part of the novel tank. A pharmacological analysis of diazepam effect in Danio rerio showed that in a certain dose range of 110 mg/l anxiolytic reduces (in comparison with the control group of fish) the number and time of freezing, increases the number of movements in the upper half of the tank and the swimming time in upper part of the tank. Diazepam causes a disinhibition of motor activity at doses of 1 and 5 mg/l, which may be explained by the effect of small doses of tranquilizers on presynaptic GABA-A autoreceptors. Diazepam 20 mg/l has a depriving effect. Conclusion. Diazepam acts in a higher dose range (110 mg/l) than phenazepam (0.11 mg/l) in Danio rerio. At the same time, diazepam is characterized by a domed dose-dependent effect, in contrast to the action of phenazepam. The prospect of using Danio rerio as an animal model in behavioral pharmacology is not inferior to studies in rodents.

We studied the effect of benzodiazepine anxiolytic phenazepam after the predator presentation to Danio rerio. The test of novelty was used: the fish was placed first in a beaker with a dissolved pharmacological substance (or H2O) and then into a novel tank for 6 min, where the trajectory, the path length, the number of movements to the upper part of the novel tank, the number and time of the pattern of freezing were measured. It is shown that, in response to the novelty of tank, the fish are reacted by submerging to the bottom, increasing the frizing, and reducing the number of movements to the upper half of the novel tank. After phenazepam administration, the fish were not only in the lower, but also in the upper part of the novel tank. The average path length did not change significantly in the range of doses used. The number and time of the frizing, as well as the time spent in the lower part of the novel tank, decreased more than 2 times compared to the control group of animals and showed a dose-dependent effect. The number of movements to the upper part of the novel tank for the experiment increased significantly from 1 in the control to 57 after phenazepam in a dose of 1 mg/l. At the same time, the number of movements of fish to the upper part of the novel tank significantly increased more than 2 times from 3th min of the experiment with the use of phenazepam in a dose of 1 mg/l. Predator presentation (Hypsophrys nicaraguensis) caused an increase in the number of freezing (temporary immobilization) and a decrease in the length of the trajectory of movement in the novel tank as compared with the Danio rerio control group. Phenazapam at a dose of 1 mg/l removed the effects of a predator, while exhibiting a typical effect: the number of movements to the upper part of the tank during the experiment significantly increased to 30; the time at the bottom of the tank was halved. It was concluded that the novelty stress test and the test with a predator are highly sensitive for studying anxiety-phobic reactions in Danio rerio.