[Mariana (OP)]

Jon wants to know:

How can 'cold-blooded' croakers be so active in the cold?

Each spring, the day after the ice clears, the first set of croakers appear in my pond. They spend about a week there, mating frantically. They swim around energetically in water that cannot be more than a few degrees above freezing.
I was always taught that "cold blooded animals" are sluggish in the cold, but they are not sluggish at all. Is my sense that cold blooded creatures are sluggish wrong? Are these frogs cold blooded?  What does it mean to be cold blooded?  (I take it to mean that they do not automatically regulate their body temperature to be a fixed/optimal temperature, but rather their body temperature is essentially ambient, perhaps a bit more in the sun, or while exercising strenuously).

Can you help answer this question?

[Mariana (OP)]

Dear Jon,

There was some discussion about 'cold-blooded' animals and what that means in our latest Q&A, broadcast on 10 February and published as a podcast on 12 February.

This is the link to it: https://www.thenakedscientists.com/podcasts/naked-scientists-podcast/zooa-why-cant-dogs-eat-chocolate [nofollow]

[AnnaScott]

And how "ice fish" lives - the distinctive features of ice fish include the fact that it has transparent blood, as well as virtually no bones, with the exception of the ridge. Cold frogs, amphibians, and others cope with cold water and at the same time have time to multiply.

[evan_au]

A discussion on ice fish from the South Pole:
https://www.sciencefriday.com/segments/this-antarctic-fish-has-blood-as-white-as-snow/

Many of these creatures that are active in cold environments have natural antifreeze in their cells, and sometimes enzymes that are optimised to operate at lower temperatures.

[AnnaScott]

The answer is worth. You have very correctly formulated a clear answer for everyone.