Predation is an important interaction for the regulation of population dynamics due to the effect caused by the direct consumption of prey. However, some populations present strategies to detect risk of predation and react to the predator. Our objective was to evaluate the effect of the predation risk of Belostoma dentatum (Mayr), under the behavioral response of the red-eye tetra fish, Moenkhausia sanctaefilomenae (Steindachner), to the availability of refuge and the density of prey. We tested the hypothesis that the distance between prey and predator decreases if there is refuge and if the individual is in a group. We observed the position of M. sanctaefilomenae in relation to the water slide. In the first treatment, we added a predator; in the second, we included refuge; and in the third, we added two more fish. The occupation pattern inside the container was only detected in the presence of the predator. With the addition of the predator, the prey was restricted to the refuge. With the removal of refuges, the distance between predator and prey remained the maximum. On the other hand, when the two new individuals were added, the occupancy pattern was no longer detected, indicating the dilution effect on group behavior. These aspects indicate that in the face of the risk of predation by B. dentatum, the individual M. sanctaefilomenae may adopt different behavioral strategies, suggesting that they are able to perceive the predator and, thus, modify prey behavior. Prey are apparently interpreting environmental cues to increase chances of survival.