A transgenic variety (red glofish) of the aquarium fish, zebra danio (Danio rerio) and wildtype zebra danios were exposed to the natural climate of north Texas in four, outside, 10,000-L microcosms during the winter of 2004–2005. At least 13 of 68 fish survived at temperatures as low as 7.5 C; however, none survived a 4 d exposure to 4 C following a cold front. These field results corroborate laboratory findings that the lowest temperature that these two varieties of D. rerio can survive is about 5 C.