ABSTRACT
First, we shall wonder why we should consider feeding rhythms after all. On one hand, we should note that food is hardly constantly available in the natural environment, being usually restricted to a particular time when food availability is highest. On the other hand, fish must trade off between food availability and the occurrence of predators, which is also highest at a certain time. Under such a cyclic environment, fish have evolved time keeping mechanisms to predict feeding time and so their physiological processes can be activated in advance, allowing the animal to avoid risk or exploit a given food source more efficiently (Madrid et al., 2001). Indeed, fish are not active throughout the 24 hours, but they usually display most of their activity along the light or the dark phase. These behavioral patterns in many species have been fixed genetically due to the pressure generated by stable selective forces such as avoidance of predators, the availability of preys or the optimization of food (Daan, 1981).
