Cold tolerance in sealworm ( Pseudoterranova decipiens) due to heat-shock adaptations.

Third-stage larvae of Pseudoterranova decipiens commonly infect whitefish such as cod, and the parasite can be transferred to humans through lightly prepared (sushi) meals. Because little is known about the nematode's cold tolerance capacity, we examined the nematode's ability to supercool, and whether or not cold acclimation could induce physiological changes that might increase its ability to tolerate freezing conditions. Even if third-stage Pseudoterranova decipiens larvae have some supercooling ability, they show no potential for freezing avoidance because they are not able to withstand inoculative freezing. Still, they have the ability to survive freezing at high subzero temperatures, something which suggests that these nematodes have a moderate freeze tolerance. We also show that acclimation to high temperatures triggers trehalose accumulation to an even greater extent than cold acclimation. Trehalose is a potential cryoprotectant which has been shown to play a vital role in the freeze tolerance of nematodes. We suggest that the trehalose accumulation observed for the cold acclimation is a general response to thermal stress, and that the nematode's moderate freeze tolerance may be acquired through adaptation to heat rather than coldness.