Critical thermal minima (CTMin) were determined for subadults of Penaeus merguiensis acclimated at 15, 18, 21 and 24 àfor 3 weeks. The effect of cooling rate on CTMin was also investigated. The CTMin of prawns from these respective acclimation groups were 5.3, 6.0, 7.4, 9.0 and 4.7, 5.4, 6.0, 7.3 àat the cooling rate of 1 àh1 and 3 àh1 respectively. Both acclimation temperature and cooling rate had a significant effect (P < 0.01) on the CTMin. Observation during the acclimation period showed that the growth rate of prawns acclimated at 24 àwas much higher than those acclimated at 21, 18 and 15 î The results indicate that P. merguiensis can overwinter in aquaculture ponds in southeast Queensland, Australia, or other subtropical areas and attain good growth if simple overwintering facilities are available.