Critical thermal minima (CTMin) were determined for the Pacific white shrimp Litopenaeus vannamei juveniles from four different acclimation temperatures (15, 20, 25, and 30 degrees C) and salinities (10 parts per thousand, 20 parts per thousand, 30 parts per thousand., and 40 parts per thousand). The lowest and highest CTMin of shrimp ranged between 7.2 degrees C at 15 degrees C/30 parts per thousand and 11.44 degrees C at 30 degrees C/20 parts per thousand. at the cooling rate of 1 degrees C h(-1). Acclimation temperature and salinity, as well as the interaction of both parameters, had significant effects on the CTMin values of L vannamei (P < 0.01). Yet, the results showed a much more profound effect of temperature on low thermal tolerance of juveniles. Only 40 parts per thousand salinity had an influence on the CTMin values (P < 0.01). As the acclimation temperature was lowered from 30 to 15 degrees C thermal tolerance of the shrimp significantly increased by 3.25-4.14 degrees C. The acclimation response ratio (ARR) of the Pacific white shrimp exposed to different combinations of salinity and temperature ranged between 0.25 and 0.27. When this species is farmed in sub-tropical regions, its pond water temperature in the over-wintering facilities (regardless of the water salinity level) must never fall below 12 degrees C throughout the cold season to prevent mortalities. (C) 2010 Elsevier Ltd. All rights reserved.