Critical thermal minima of alligator gar (Atractosteus spatula, [Lacépède, 1803]) during early life stages

Summary Water temperature controls a plethora of morphological and metabolic functions in fishes and studies examining thermal tolerance of fishes and the responses of fishes to changing water temperatures have been conducted for over a century. Although there has been a renewed interest in the management and conservation of alligator gar, currently there are no data regarding the thermal minima of the species. In this study, we obtained alligator gar juveniles from a hatchery setting, acclimated these fish to three separate water temperatures (21, 24.5, and 28°C) and then subjected them to critical thermal minima trials to quantify lower thermal tolerance. Critical thermal minima results were found to be related with acclimation temperature and total length. Less developed gar experienced equilibrium loss at higher temperatures than larger, more developed gar. Also, alligator gar in the coldest acclimation trials (21°C) were able to tolerate the lowest temperatures. The mean CTmin temperature values obtained for each acclimation trial were 11.57°C, SD = 1.39 (21°C), 12.83°C, SD = 1.47 (24.5°C), and 14.16°C, SD = 1.60 (28°C). This study helps to fill an important data gap in alligator gar life history, and our results could be beneficial for management of alligator gar and determining potential future range distributions.