Upper and lower temperature tolerance limits for juvenile red drums from texas and south carolina

Upper and lower temperature tolerance limits, reported as temperatures lethal to 50% of the test fish (LT50s), were determined for juveniles of red drum Sciaenops ocellatus obtained from Texas and South Carolina brood stock. This information on red drum thermal tolerance limits was used to determine whether a more northerly distributed population exhibits greater cold tolerance and could therefore be used to improve success of stocking programs. A 96-h temperature tolerance test was performed on juveniles (71-155 mm total length) acclimated to water temperatures ranging from 12.0 to 28.0°C at a salinity of 20%o. Test fish were transferred directly into a series of high-temperature (27.0-37.0°C) or low-temperature (2.0-16.0°C) water baths. The upper LT50 for Texas red drums acclimated to 28.0°C was within 1.1°C of that calculated for South Carolina red drums acclimated to the same temperature (upper LT50s were 35.7 and 34.6°C). Upper LT50s for fish acclimated to 20.0 and 12.0°C were also similar between the two stocks. Likewise, lower LT50s were similar between the two stocks of red drums: as determined from fish acclimated to 14.0 and 28.0°C, ranges of lower LTSOs were 2.8-9.0°C for the Texas stock and 2.6-9.3°C for the South Carolina stock. The lower LT50 could not be determined for red drums acclimated to 12.0°C, because only three fish died. No consistent differences in temperature tolerance limits were found between the two hatchery stocks, precluding any recommendation to stock one group instead of the other.