Texas stocks of northern and Florida largemouth bass (Micropterus salmoides salmoides and M. s. floridanus) were compared for resistance to cold shock. The 45 advanced fmgerlings of each subspecies had nearly identical rearing histories and were acclimated to a common temperature near 21 C. Laboratory tests were conducted at constant temperatures ranging from 5.3 to 13.5 C. Over all tests, more than twice as many Florida bass as northern bass died during the 7 days ofobservation. Weestimated that the 96-h median tolerance limit was about 6 C for northern bass and about 8.5 C for the Florida bass. These fmdings are consistent with the hypothesis that Florida bass stocked outside their original range may suffer higher overwinter mortality, owing to lesser cold tolerance, than native northern bass.
