Photoperiod and temperature are two of the most powerful environmental cues that entrain circadian clocks. Being ectothermic, fish must keep their body temperature within a physiological range to optimize biological processes mainly applying behavioral strategies. Here, we developed a low-cost, automated system that allows to create a horizontal multiple-step thermal gradient and video record fish behavior for long-term periods. To validate the system, we assessed daily thermal preference and locomotor activity in the teleost