Fish, as a basal group within vertebrates, are excellent models to explore the integration mechanisms of the environmental and social keys of biological rhythms.

We investigate circadian and seasonal rhythms in two animal models subjected to extreme environmental conditions that impose different challenges on the biological clock: electric fish (Gymnotus omarorum) exhibit daily rhythms of locomotor activity and electrical behavior in a natural environment in permanent darkness, while Annual fish (Austrolebias reicherti) face their biological clock in an extremely dynamic environment, with enormous seasonal variations in light, temperature, conductivity and turbidity.