Thermal Adaptation - Antifreeze Glycoprotein

The Antarctic Icefish (Dissostichus Mawsoni) is a cryophilic (cold-loving) fish species endemic to the Southern Ocean. They are stenothermic, meaning that they can only survive in limited environmental temperatures. The Southern Ocean varies between -1.9 and 3°C (Deacon 1984; Eastman 1993). Antarctic Icefish can grow to over 2 metres in length and reach 40 years of age (Brooks et al. 2010). How does a fish that lives in sub-zero arctic temperatures survive for 40 years? This blog post will address the adaptations of the Antarctic Icefish and how it thrives in extreme cold.

Fig. 1: Antarctic Icefish (Dissostichus Mawsoni) next to a Bald Notothen (Pagothenia Borchgrevinki)

(Fields 2012)

The Antarctic Icefish belongs to a suborder of ‘white-blooded’ fishes called Notothenioids. The evolution of Notothenioids has resulted in several biological adaptations allowing them to maintain circulatory and cellular function (Beers & Jayasundara 2015). Notothenioids possess ‘antifreeze’, a glycoprotein which prevents the growth of ice crystals by binding water molecules to them in the blood (Russo et al. 2010). This process is known as adsorption inhibition, likened to by DeVries as “putting a silk-stocking around the ice crystal” (Goodman 1998). Notothenioids also have membranes and specifically cold-adapted proteins to maintain metabolic rate.

The Antarctic Icefish has evolved so specifically to cold waters, that it is foreseeable that climate change will present significant threats to not only Notothenioid species, but other cryophilic marine organisms. The heat tolerance of Antarctic fishes was first studied by Somero and DeVries (1967) who determined the upper incipient lethal temperature (UILT) in three species of Notothenioids; the Striped Rockcod (Trematomus hansoni), Emerald Rockcod (Trematomus bernacchii) fishes and the Bald Notothen (Pagothenia Borchgrevinki) (Bilyk 2011). These fishes shared UILT values of only 5-7°C after being acclimatised to habitual arctic temperatures of -1.9°C. The heat intolerance of marine invertebrates such as a species of Brittle Starfish (Ophionotus victoriae) is more concerning, with fatalities recorded when subjected to temperatures as low as 2°C (Bilyk 2011).

The Antarctic Icefish has evolved with specialised biochemical adaptations which allow it to thrive in its sub-zero habitat. However, the icefish along with other species in its ecosystem will be threatened with extinction as global warming increases the temperature of the Southern Ocean.

References:

Beers, J. M. and Jayasundara N, 2015, ‘Antarctic notothenioid fish: what are the future consequences of ‘losses’ and ‘gains’ acquired during long-term evolution at cold and stable temperatures?’, The Journal of Experimental Biology (2015), pages 1834-1845

Bilyk, K. T. DeVries, A. L. 2011, ‘Heat tolerance and its plasticity in Antarctic fishes’, Comparative Biochemistry and Physiology, Part A 158 (2011) pages 382–390

Brooks, C. M, Andrews, A. H, Ashford, J. R, Ramanna, N, Jones, C. D, Lundstrom, C. C, Cailliet, G. M, 2010. ‘Age estimation and lead–radium dating of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea’, Polar Biology

Deacon, G., 1984. ‘The Antarctic Circumpolar Current’. Cambridge University Press, Cambridge.

Eastman, J.T., 1993. ‘Antarctic Fish Biology: Evolution in a Unique Environment’ Academic Press, San Diego.

Goodman, B. 1998, ‘Where Ice Isn't Nice’, BioScience, Vol. 48, No. 8 (Aug., 1998), pages 586-590

Russo, R. Riccio, A. Di Prisco, G. Verde, C. Giordano, D. 2010, ‘Molecular adaptations in Antarctic fish and bacteria’, Polar Science 4 (2010), pages 245-256

Figures: 

Fields, L. G. 2012, ‘“Mortimer Bob” with a borch for scale’, photograph viewed 19/03/2016