October 25, 2013 in Uncategorized
Chaenocephalus aceratus & family Channichthydiea
(Photo 1, of the family Channichthydiea, commonly know as Antarctic Ice fish)
Chaenocephalus aceratus is a fish with clear blood. It belongs to a family of sixteen known members of the Channichthydiea (common, Antarctic Icefish), sub order Nototheioidei. The Channichthydiea are peculiar possessing a gene mutation that stopped the production of haemoglobin – normal in the oxygen/blood transport system. This gene mutation and a variety of environmental factors are thought to be responsible for the interesting physiological development of the Channichthydiea as a whole and Chaenocephalus aceratus in particular. There have been recent concerns over global temperature rise. Chaenocephalus aceratus’ unusual physiology might be particularly useful to look at when studying fish stress in response to changes in the ocean environment.
Chaenocephalus aceratus overview
Chaenocephalus aceratus was discovered by Ditlef Rustad, a zoologist researching near Bouvet Island, Antartica, 1928, (Jabr, 2012). Immediately noticeable was that this fish had major differences with other known Antarctic fish. The fish had no swim bladder, the skin was scale-less, tissues were translucent, gills white and, most notable, the fish exhibited colourless blood. It is now known that a gene mutation occurred to suppress the haemoglobin making function within the now known family Channichthydiea. This lack of pigmented protein throughout the tissue layers allows light to pass though virtually uninhibited giving a glassy look and apt common name – the ice fish- as can be seen in photo 1 & photo 3. Much work has since been carried out on Chaenocephalus aceratus to discover how such an organism was able to evolve and thrive in the now exacting and hostile marine Antarctic climate.
Photo 1, Chaenocephalus aceratus, www.bbc.co.uk
The Antarctic environment has changed significantly over the last +/- 40 million years (Eastman, 2005) and as the continental land mass moved toward the south pole. The fossil record emerging from Antarctica supports the theory that the earlier environment was warmer, likely bio-diverse rich and populated with organisms that were poor at adapting fast to local climate change as the continent cooled to the harsher modern climate. Global fluctuations and then rises in planet oxygenation impacted on both marine and atmospheric environments. (Holland, 2006) Changes in climate and ocean currents had a marked effect on Antarctica culminating in the formation of both an ice sheet over Antarctica and of the formation of opposing circumventing currents around Antarctica known as the coastal Polar Current (anticlockwise) and Antarctic Circumpolar Current (clockwise), (Denny, 2008), see map 1., (Team, 1993)
Map 1 Showing the two polar currents encasing the Antarctic continent, Polar Current moving anti clockwise, Circumpolar Current, clockwise.
The cooling marine environment allowed for greater oxygen solubility in sea water resulting in oxygen rich waters. Water cooling deterred or killed off much the historic marine biodiversity of the Antarctic continent and the opposing Antarctic current system effectively trapped in the adapting organisms. Thus limited, trapped, adapting marine species were left to acclimatise in the emerging colder, oxygen rich environment. The threat of predation decreased as historic predators unable to adapt to the new conditions were naturally removed from the locale. Ecosystem niches in the benthic layer and water column historically held by temperate favouring marine organisms had been vacated and had become available for occupation by local inhabitants such as the Nototheioidei with Chaenocephalus aceratus eventually taking posts on the sea floor.
Physiological coping mechanisms for Chaenocephalus aceratus
Chaenocephalus aceratus has developed strategies for survival in Antarctic waters. These included maximizing oxygen uptake, albeit as a response to a lacking haemoglobin, and developing Antifreeze proteins (AFP), insurance against freezing to death in icy waters.
The colourless, haemoglobin free blood of the Chaenocephalus aceratus, see Photo 3, test tube to the right.
Photo 3, Photo Kristin O’Brien. Test tubes containing blood drawn from two related Antarctic fish, the one on the right from an Ice fish.
arose due to a gene mutation thought to have occurred between 10-12 million years ago (mya), (Bruce D. Sidell, 2006). Oxygen is therefore not bound to blood proteins, as with hemoglobin in other Nototheioidei, but moved as a solute. Noticeable in the anatomy of the modern Chaenocephalus aceratus is an enlarged heart, more than four times greater in size than the heart of a comparable Nototheioidei cousin. Accompanying the bigger pump is a more extensive and capacious capillary system, to transport the blood at approximately four times greater flow. (Bruce D. Sidell, 2006). The lack of blood proteins makes the blood less viscous and therefore less prone to sluggishness in the cold. The high partial pressure of dissolved oxygen in the surrounding water plus the scale free skin of Chaenocephalus aceratus, also allows for oxygen transfer through the fish skin. It is suggested that the resulting blood/oxygen transport system evolved because of unfavourable gene mutation rather than a response to the environmental situation, (Bruce D. Sidell, 2006).
Antarctic fish inhabiting the southern reaches of the Ross Sea experience an almost constant mean annual temperature of -1.86’C, (Wilson, 2002). If temperature is seen to be constant then there is a potential motivator for evolving out the unnecessary mechanisms used to regulate (previously) fluctuating body temperatures. Differing studies conducted by (Wilson, 2002) and (Kevin T. Bilyk*, 2011) indicates that Antarctic fish and Antarctic Nototheioidei in particular have extremely low tolerances to heat increase, (Wilson, 2002). A suggestion is that Antarctic fish including Chaenocephalus aceratus have evolved their temperature regulation mechanisms to become redundant.
Sea Water freezes at around -2;C. The potential of ice-crystals forming, puncturing cell walls, piercing flesh and resulting in death is very real for marine fauna. However Antarctic fish possess antifreeze proteins (AFP) which seem to inhibit the growth of ice crystals and actually bind the ice into its fatty layer (Fletcher, et al., 2001). So whilst tolerance for heat rise is not currently an effecting factor for the Chaenocephalus aceratus of Antarctica the ice rich waters seems to have promoted evolution of antifreeze proteins (AFP) to keep the fish ice cold but not frozen.
Chaenocephalus aceratus of the family Channichthydiea have evolved and become successful in a climate too cold-hostile for other fauna to bear by investing in antifreeze proteins [(AFP), fats] with which to insulate itself with. In addition the Antarctic Ice fish compensated against the loss of genetic function (that historically supported the superior transport of oxygen to body tissues) by physically growing its blood transport system.
There is ongoing concern, in some quarters, regarding global temperature rises and the repercussions for the worlds’ ecosystems (Intergovernmental Panel on Climate Change, 2013). Chaenocephalus aceratus is uniquely placed to give early warning with regard to changes in the Antarctic micro climate it currently inhabits. A shift in climate patterns globally is likely to have an effect on the currents surrounding the Antarctic continent disturbing the natural closed ecosystem defences, the nutrient dispersal, the stability of water temperature and potential release of oxygen into less oxygenated waters or the atmosphere. Warmer waters may well encourage more temperate dwellers towards the Antarctic. Any fast rise in temperature above 4’C is likely to kill the family Channichthydiea. If heat doesn’t bring about demise then the rise in temperature may well cause super oxidation and death of fish tissues (Ansaldo, et al., 2000). Predation from outside visitors or competition by visitors for food may negatively impact on the fish. De-oxygenation of the Antarctic waters may leave Chaenocephalus aceratus and its family Channichthydiea literally gasping for breath (Hans O. Portner et al, 2006). However the author believes any study worth commenting on needs conducting over a geological time period to fully appreciate the capacity of this family to evolve in response to its changing environment.
Photo 4, Chaenocephalus aceratus on the sea bed
Ansaldo, M., Luquet, C., Evelson, P. & al., e., 2000. Antioxidant levels from different Antarctic fish caught around South Georgia Island and Shag Rocks. POLAR BIOLOGY Volume: 23 Issue: 3 , pp. Pages: 160-165.
Bruce D. Sidell, K. M. O., 2006. When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes. The Journal of Experimental Biology.
Denny, M., 2008. How the Ocean Works. Princeton: Princeton University Press.
Eastman, J. T., 2005. The Nature of the diversity of Antarctic Fishes. Polar Biology, Volume 28, pp. 93-107.
Fletcher, G., Hew, C. & Davies, P., 2001. Antifreeze proteins of teleost fishes. ANNUAL REVIEW OF PHYSIOLOGY, pp. 359-390.
Hans O. Portner et al, 2006. Climate – dependent evolution of Antarctic ectotherms. An integrative analysis. Elsevier, Deep Sea Research II, Volume 53, pp. 1071-1104.
Holland, H. D., 2006. The Oxygenation of the atmosphere and oceans. PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY BIOLOGICAL SCIENCES, pp. 903 – 915.
Intergovernmental Panel on Climate Change, 2013. http://www.ipcc.ch/report/ar5/wg1/#.UmmtYX5waP8. [Online]
Available at: http://www.ipcc.ch/report/ar5/wg1/#.UmmtYX5waP8
Jabr, F., 2012. How the Antarctic Icefish Lost Its Red Blood Cells But Survived Anyway. [Online]
Available at: http://blogs.scientificamerican.com/brainwaves/2012/08/03/how-the-antarctic-icefish-lost-its-red-blood-cells-but-survived-anyway/
Kevin T. Bilyk*, A. L. D., 2011. Heat Tolerance and its plasticity in Antarctic fishes. Elsevier, Comparative Biochemistry and Physiology, Part A, Volume Part A, pp. 382-390.
Team, m. f. t. O. U. C., 1993. http://www.eng.warwick.ac.uk/staff/gpk/Teaching-undergrad/es427/rice.glacier.edu-oceans/GLACIER%20Oceans-%20–%20Antsurfwater.htm. [Online]
Available at: http://www.eng.warwick.ac.uk/staff/gpk/Teaching-undergrad/es427/rice.glacier.edu-oceans/GLACIER%20Oceans-%20–%20Antsurfwater.htm
Wilson, e. a., 2002. Turning up the heat on subzero fish: thermal dependence of sustained swimming in an Antarctic notothenioid. Journal of Thermal Biology, pp. 381-386.