Thermal Preferences and Critical Temperatures of Invasive Lionfish Complex (Pterois volitans/P. miles)

Acute temperature preference and thermal limits were determined for locally captured, juvenile lionfish at four different acclimation temperatures (13°C, 20°C, 25 °C and 32°C). Temperature preferences were evaluated using an automated shuttlebox system that presents temperature stimuli in a subject-driven fashion. Subjects control the temperature with their movement throughout the tank. Acute preference was calculated as the mean temperature that the fish occupied during the first two hours of dynamic experimentation. Critical thermal methodology was used to determine the CTmin and CTmax of the lionfish with loss of equilibrium (LOE) as the endpoint. It is assumed that beyond this temperature, the fish would be unable to survive. Temperature was increased or decreased by 0.33°C per minute until the end point was reached. Thermal tolerance polygons provide a visual representation to the lower and upper thermal avoidance temperatures of the invasive lionfish, delineating the thermal range of the species. Their CTmin and CTmax (acclimated to 25°C) were compared experimentally to two other Florida reef fish ( Cephalopholis cruentata and Lutjanus apodus ). Acute preference data can be used to estimate final preferendum. This analysis has shown a final preferendum around 27-28°C, but no significant difference of acute preferences between acclimation temperatures. Final preferendum is shown to correlate well with optimal temperatures for growth, metabolic rate, digestions, etc. Thermal tolerance describes the range of temperature in which lionfish can survive. The thermal tolerance polygon shows a strong correlation between CTM and acclimation temperature, with the highest CTmax at 39.5°C and the lowest CTmin at 9.5°C. Additionally, at 25°C, lionfish have a smaller tolerance range compared to schoolmaster and graysby.