Observations on the thermoregulatory behaviour of juvenile spotted grunter, Pomadasys commersonnii (Haemulidae: Pisces)

The thermal preference of juvenile spotted grunter, Pomadasys commersonnii (Haemulidae), was determined in a horizontal thermal gradient. Temperature preference was tested over a range of 17–31°C at three salinities. The modal temperature preferenda at 5, 12 and 35 ppt were 25°C, 24.5°C and 25°C, respectively. They were not significantly different. The thermal preferendum of this species was found to be between 24°C and 25°C. Supplementary experiments were conducted to test the stability of the final thermal preferendum. Initial observation of the behaviour of juvenile spotted grunter indicated the presence of a strong circadian rhythm. However, diel variation in activity did not influence temperature preference. These data are important for the development of a culture protocol for this euryhaline species.