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

ABSTRACT 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.