Behavioural temperature regulation is a low priority in a coral reef fish (Plectropomus leopardus): insights from a novel behavioural thermoregulation system.

Current understanding of behavioural thermoregulation in aquatic ectotherms largely stems from systems such as 'shuttle boxes', which are generally limited in their capacity to test large-bodied species. Here, we introduce a controlled system that allows large aquatic ectotherms to roam freely in a tank at sub-optimal temperatures, using thermal refuges to increase body temperature to their thermal optimum as desired. Of the 10 coral grouper (Plectropomus leopardus; length ∼400 mm) implanted with thermal loggers, three fish maintained themselves at the ambient tank temperature of 17.5-20.5°C for the entire 2-4 days of the trial. Of the other seven fish, body temperature never exceeded ∼21.5°C, which was well below the temperature available in the thermal refuges (∼31°C) and below the species' optimal temperature of ∼27°C. This study adds to a growing literature documenting an unexpected lack of behavioural thermoregulation in aquatic ectotherms in controlled, heterothermal environments.