[John Harrison]

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?

[Nizzle]

For an important chemical reaction, poikilotherms [cold-blooded animals] may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms [warm-blooded animals] 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.[citation needed] 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.

source: http://en.wikipedia.org/wiki/Poikilotherm

So to answer your question: They have specialized enzymatic systems.

[thedoc]

Listen to the answer to this question on our podcast.

[yoyo jojo]

Can cold blooded animals live in warm water??

[Henryjones]

cold blooded animals have that skin that protect them

[Kryptid]

cold blooded animals have that skin that protect them

Skin alone is insufficient for temperature regulation in a cold climate.

[charles1948]

On the "cold-blooded" point, this brings up something I've wondered about.  Dolphins.

These originated, according to conventional evolutionary theory, from ancestors that lived in the sea.  Where they were, presumably, cold-blooded.

Then these ancestors came out of the sea and evolved to live on land.  Where they became warm-blooded mammals.

Then these land-living mammals,  for not very clear reasons, took a kind of retrogressive step, by going back into the sea again.

And this brings up the thing that puzzles me.  When they went back into the sea  - why didn't they go back to being cold-blooded again?

Why did they stay warm-blooded?   I mean if they were going to retrogress by going back into the sea, shouldn't they have gone the whole hog, so to speak.  And lost not just their land-based legs, which degenerated into fins and flippers, but their entire warm-body metabolism.

And so turned into versions of comparably-sized cold-blooded fish such as sharks.

Sharks seem to do very well by being cold-blooded.  So why are dolphins still warm-blooded?

[Kryptid]

Some sharks are warm-blooded.

There are advantages to being warm-blooded over cold-blooded, such as the ability to retain high energy levels despite cold conditions. That would give them an edge when hunting cold-blooded prey or escaping cold-blooded predators.

[evan_au]

Sharks seem to do very well by being cold-blooded.  So why are dolphins still warm-blooded?

One reason is that it takes a lot of oxygen to maintain an active lifestyle and a large brain.
- This is an ecological niche which was not filled by fish
- It easier to get this oxygen from the air than it is to extract it from sea water.

Well-oxygenated surface water may only contain around 8 mg O₂/l, while the air contains 210 mg O₂/l.

See: https://rwu.pressbooks.pub/webboceanography/chapter/5-4-dissolved-gases-oxygen/