DEVRIES, A.L.*; CHENG, C.-H.C: Freezing avoidance strategies differ in Antarctic and Arctic fishes
Notothenioid fishes in Antarctica freeze at approximately -2.3oC. One degree of this freezing point depression is primarily due to NaCl, while the remainder is due to antifreeze glycoproteins (AFGP) and a recently discovered antifreeze potentiating protein (AFPP). AFGPs are present in the blood at 30 to 40 mg/ml while AFPP ranges from 2 to 4 mg/ml depending on the species of notothenioid. Only the antifreeze activity of the larger AFGPs 1-5 appeared to be potentiated, while the smaller AFGPs 7 and 8 are not. Thus fishes living in very icy shallow water like Pagothenia borchgrevinki have lower levels of AFGP 1-5 and high levels of AFPP, while Trematomus loennbergi living at 500 meters where the cold water lacks ice have high levels of AFGP 1-5 and low levels of AFPP. This relationship appears to correlate with depth and the amount of ice in the fishes environment. Arctic gadid fishes have freezing points between -1.9 and -2.1oC in the winter and also have AFGPs similar in size, composition and amount to the notothenioids but they do not have AFPP. There is no evidence of any other macromolecular antifreeze compound and thus the slightly elevated blood salt concentrations and the AFGPs appear to account for their low freezing points and freezing avoidance. In contrast, in the Antarctic notothenioids, the combination of elevated salt concentration (250mM), AFGPs and AFPP is responsible for the freezing avoidance.
