Zebrafish (Danio rerio) responds differentially to stimulus fish: the effects of sympatric and allopatric predators and harmless fish.

The zebrafish has been an excellent model organism of developmental biology and genetics. Studying its behavior will add to the already strong knowledge of its biology and will strengthen the use of this species in behavior genetics and neuroscience. Anxiety is one of the most problematic human psychiatric conditions. Arguably, it arises as a result of abnormally exaggerated natural fear responses. The zebrafish may be an appropriate model to investigate the biology of fear and anxiety. Fear responses are expressed by animals when exposed to predators, and these responses can be learned or innate. Here we investigated whether zebrafish respond differentially to a natural predator or other fish species upon their first exposure to these fish. Naïve zebrafish were shown four species of fish chosen based on predatory status (predatory or harmless) and geographical origin (allopatric or sympatric). Our results suggest that naïve zebrafish respond differentially to the stimulus fish. Particularly interesting is the antipredatory response elicited by the zebrafish's sympatric predator, the Indian Leaf Fish, and the fact that this latter species exhibited almost no predatory attacks. The findings obtained open a new avenue of research into what zebrafish perceive as "dangerous" or fear inducing. They will also allow us to develop fear and anxiety related behavioral test methods with which the contribution of genes to, or the effects of novel anxiolytic substances on these behaviors may be analyzed.