Background
The authors write that "most animals do not have a static heat tolerance; rather it changes in response to their recent thermal history through acclimation." However, as they continue, "given the long residence of Antarctic fishes in constant freezing seawater, this plasticity had long been thought either lost or marginal (Brett, 1970)." And they thus say that "given the future predicted increases in water temperatures in the southern Ocean from global climate change, understanding the heat tolerance of Antarctic fishes and its plasticity is critical for understanding the threat to this cold adapted fauna."

What was done
The critical thermal maximum (CTMax) is the temperature at which an animal loses the ability to escape from constant rapid warming (Paladino et al. 1980); and Bilyk and DeVries employed this methodology "to survey heat tolerance in a geographically diverse group of eleven species of Antarctic fishes acclimatized to the cold water temperatures of their natural habitats." And they also used this methodology on eight of the species "following warm acclimation to 4°C, which when compared to their environmental CTMaxs provided a measure of the plasticity of their heat tolerance," as they say that these fish "had been caught or held at temperatures below -0.9°C."

What was learned
The two researchers report that "when acclimatized to their natural freezing water temperatures, environmental CTMaxs ranged from 11.95 to 16.17°C," and that when the eight further-studied species were warm-acclimated to 4°C, they found that "all showed a significant increase over their environmental CTMaxs, with several showing plasticity comparable in magnitude to some far more eurythermal fishes."

What it means
Bilyk and DeVries say that "despite their low CTMaxs, all the Antarctic species maintained the capacity to increase their heat tolerance through warm acclimation," and they state that when this capacity was quantified, it showed "a surprising level of thermal plasticity at low temperatures," which they say was further surprising "given the presumed loss of selection for thermal flexibility that has long been assumed in this fauna." So even the coldest of the cold, it would appear, are ready to accept whatever challenges a warming world might present to them.

References
Brett, J.R. 1970. Temperature. Marine Ecology 1: 515-560.

Paladino, F.V., Spotila, J.R., Schubauer, J.P. and Kowalski, K.T. 1980. The critical thermal maximum -- a technique used to elucidate physiological stress and adaptation in fishes. Reviews of Canadian Biology 39: 115-122.