Critical thermal minima (CTmin) values were determined for the Pacific white shrimp Litopenaeus vannamei juveniles at combination of four different acclimation temperatures (15, 20, 25, and 30°C) and salinity levels (10, 20, 30, and 40‰). The lowest and highest CTmin of shrimps ranged between 7.2°C at 15°C/30‰ and 11.44°C at 30°C/20‰ at cooling rate of 1°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‰ salinity had an influence on the CTmin values (P<0.01). As the acclimation-temperature was lowered from 30°C to 15°C, the thermal tolerance of the shrimp significantly increased up by 3.25–4.14°C. The acclimation response ratio (ARR) of the Pacific white shrimp exposed to different combinations of salinity and temperature ranged from 0.25 to 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°C throughout the cold-season to prevent mortalities.
Critical thermal minima (CTMin) and maxima (CTMax) values were determined for the Pacific white shrimp Litopenaeus vannamei post-larvae and juveniles at four different acclimation temperatures (15, 20, 25, and 30 °C). The CTMin of shrimp at these acclimation temperatures were 7.82, 8.95, 9.80, and 10.96 °C for post-larvae and 7.50, 8.20, 10.20, and 10.80 °C for juveniles, respectively, at 1 °C/h cooling rate. The CTMax values were 35.65, 38.13, 39.91, and 42.00 °C for post-larvae and 35.94, 38.65, 40.30, and 42.20 °C for juveniles at the respective acclimation temperatures. Both acclimation temperature and size of the shrimp affected CTMin values of L. vannamei (P<0.01). Overall, juveniles displayed significantly lower CTMin values than the post-larvae (P<0.0001). However, the CTMax response by post-larvae and juveniles were not significantly different from each other and no interaction was determined between the acclimation temperature and development stage (P<0.01). The area of the thermal tolerance polygon over four acclimation temperatures (15, 20, 25, and 30 °C) for the post-larvae of L. vannamei was calculated to be 434.94 °C. The acclimation response ratio (ARR) values were high ranging from 0.35 to 0.44 for both post-larvae and juveniles. L. vannamei appears to be more sensitive to low temperatures than other penaeid species and its cold tolerance zone ranged from 7.5 to 11 °C. In successful aquaculture temperature must never fall below 12 °C to prevent mortalities. Upper thermal tolerance is less of a problem as in most subtropical regions maximum water temperature rarely exceeds 34 °C, but care should be given if shallow ponds with low water renewal rate are being used.
Link to article, http://www.sciencedirect.com/science/article/pii/S0306456510000653