An Automated Low-Cost Solution for Creating a Multiple-Step Thermal Gradient to Record Daily Fish Thermoregulatory Behavior.

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 Danio rerio. Our apparatus provides the opportunity to investigate the behavioral thermoregulation of captive fish, and our results highlight the importance of considering thermal preferences when designing husbandry protocols.