Science Questions

How do cold-blooded species cope in cold water?

Sun, 11th Oct 2009

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John Harrison asked:

How do cold-blooded species cope in cold water? We all know that reptiles have to sun themselves to build up the energy or ability to sustain their activity and to get to the right temperature. And this is attributed to the fact that theyíre cold-blooded. How is it then possible for other cold-blooded species like fish and invertebrates like octopus, squid and so on to sustain the high levels of activity that they do, that they can live in near freezing or actually freezing water?


The answer is to do with their metabolic rates and the fact that they can operate at those low temperatures.  I actually want to go into detail a little bit on what you call at the end, the freezing species.  This is the most interesting thing that was discovered back in the 1960s which is that there are fish in the Antarctic that create antifreeze and thatís how they live in very cold temperatures.  Because the crazy thing about the sea is that it doesnít actually freeze until -1.9 degrees centigrade where as normally water freezes at zero, we know that.  But itís because of those salts and the various impurities in seawater that means that ocean temperatures can get extremely low indeed especially down there in the southern ocean.  And so these Antarctic cod it was discovered that they have glycoproteins in their blood.  That means that their tissues their fluids inside them donít freeze until -2 degrees centigrade, so they are safe in the sea.  The glycoproteins work in a very clever way by actually attaching to the surface of small ice crystals by plugging gaps if you like between them.  And that stops them from getting any bigger so the fish themselves donít actually freeze despite the fact that they are sub zero in temperaturesand thatís really rather cool.  But then there are other reasons why they donít actually manage to swim around all the time and they are affected to some extent by what temperature there is and whatís going on in the environment.  Because it was discovered last year that some fish in the Antarctic hibernate.  The first fish that were shown to actually slow down, slow their heart rate, slow their movements when itís very cold and dark.  And that could actually be because itís dark and they need to be able to see to be able to catch their food.  So in fact what they do is say, ďOkay fine weíll have a bit of rest while we canít find our food and wake up when it gets warmer and lighter.Ē


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John Harrison asked the Naked Scientists: Cold Bloodedness: We all know that reptiles must sun themselves in order to build the energy / ability to sustain activity. This attribute is generally attributed to the fact that they are cold blooded. How then is it possible for other cold-blooded species (fish, invertebrates such as octopus, squid, etc.) to sustain high levels of activity in near freezing water? What do you think? John Harrison, Fri, 26th Jun 2009

For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. Frogs are a notable example of this effect.

Because their metabolism is so variable, poikilothermic animals do not easily support complex, high-energy organ systems such as brains or wings. Poikilothermic animals do not use their metabolisms to heat or cool themselves. For the same body weight, poikilotherms need half to 1/10 of the energy of homeotherms, and thus eat half to 1/10 of the biomass.


So to answer your question: They have specialized enzymatic systems. Nizzle, Tue, 18th Aug 2009

Can cold blooded animals live in warm water????? yoyo jojo, Wed, 5th Mar 2014

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