LAUSR

To investigate the effect of hypothermal (22 → 16 °C) and hyperthermal (22 → 28 °C) stress on the energy regulation of Litopenaeus vannamei cultured in long-term freshwater, the activities of hexokinase (HK), pyruvate kinase (PK), lactic dehydrogenase (LDH), and succinate dehydrogenase (SDH) were determined and compared with those kept in seawater. Results showed that at the early stage of thermal stress, HK, PK, and LDH activities increased and then decreased. At the end of the trial (48 h), all enzyme activities except PK and LDH activities in shrimps cultured in freshwater returned to the pre-experiment level. Following temperature stress, SDH activity of shrimps cultured in freshwater and seawater all decreased first and then increased, and finally reached the pre-experiment level, while SDH activity in gills of shrimps cultured in seawater was significantly lower than that before. At a constant temperature of 22 °C, compared with shrimps cultured in seawater, those cultured in freshwater had a lower level in HK, PK, and SDH activities, but a higher level in LDH activity. In summary, shrimps cultured in freshwater might rely more on anaerobic metabolism, while the opposite was true for glycolysis and aerobic metabolism. Because shrimps cultured in freshwater had a higher sensitivity to thermal stress, noticeable temperature variation especially when temperature decrease should be avoided in the freshwater intensive culture of L. vannamei.