Influence of salinity on the thermal preference of juvenile thinlip mullet, Chelon ramada.

Changes in environmental conditions resulting from climate change are linked to shifting species' distribution ranges. While water temperature is a well-established determinant of fish biogeography, the role of salinity has received comparatively less attention, while there is ample evidence that salinity tolerance is temperature-specific. Grey mullets (Mugilidae family) are considered climate change indicator species due to their strong temperature dependence. Although mullets are euryhaline, salinity gradients have been shown to spatially structure grey mullet communities, potentially influencing their distribution and interactions with thermal niches. To improve predictions of how mullets may respond to climate change, we examined how salinity influences temperature preference in juvenile thinlip mullet ( Chelon ramada )—a euryhaline species common to temperate estuaries. Using a circular water temperature preference chamber, we found that juvenile C. ramada consistently preferred a temperature of 26.2 ± 0.1 °C, independent of salinity treatments (5 and 25 g/kg). This was contrary to osmoregulatory theory, which predicts that salinity may influence thermal preference due to the energetic cost of maintaining homeostasis. Instead, our findings indicate that, within the tested range, salinity does not modulate thermal preference in juveniles—suggesting that temperature alone may be a sufficient predictor of habitat selection under future climate scenarios. These results provide novel, species- and size-specific insights that can directly inform model predictions of thinlip mullet distribution in warming estuarine and coastal systems. • Osmoregulatory theory was tested in a climate change indicator species. • Behavioral thermoregulation was studied using a circular water temperature chamber. • Mullet preferred 26.2 ± 0.1 °C, independent of salinity treatments (5 and 25 g/kg).