Temperature Tolerances of Wild‐Type and Red Transgenic Zebra Danios

Seventy‐nine transgenic red zebra danios Danio rerio (also known as zebrafish; transgenics also known as glofish) and 78 wild‐type zebra danios acclimated to 20°C and 30°C had critical thermal maxima (±SD) of 38.8 ± 0.54°C and 41.3 ± 0.50°C (glofish) and 39.2 ± 0.34°C and 41.7 ± 0.35°C (wild‐type), respectively. The critical thermal minima (±SD) were 7.2 ± 0.48°C and 10.0 ± 0.50°C (glofish) and 6.2 ± 0.28°C and 10.6 ± 0.53°C (wild‐type), respectively. At both 20°C and 30°C acclimation temperatures, critical thermal maxima (CTMax) and critical thermal minima (CTMin) were significantly different between transgenic and wild zebrafish; however, differences were 1°C and less. The temperature tolerances would classify both varieties of zebra danios as eurythermal and place this species in the relatively rare category of fishes with a CTMax above 40.0°C. Compared with similar temperature tolerance data reported for other tropical fishes that have successfully been introduced into U.S. waters, the present data suggest both wild‐type zebra danios and red glofish are capable of overwintering in some southern U.S. waters.