# Tropical fish cant live in cold waters



## acestro (Jul 7, 2003)

Honestly I have guesses and theories but I cant remember if this has ever been explained to me in a convincing fashion.

Anyone know? Curious about your guesses as well.


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## BlackSunshine (Mar 28, 2006)

because they cannot produce their own internal heat and their organs are adapted to certain enviroments. If a tropical goes into cold his organs start to shut down as does his metabolizim.
This is also why If you feed a tropical fish frozen chunks of food it could place him into shock because it cools his body rapidly.


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## mr_rob_boto (Aug 31, 2003)

oh damn... I'm going to have to let those chunks thaw from now on. Good to know though


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## acestro (Jul 7, 2003)

So.... minnows produce their own internal heat? I dont think that's true.


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## BlackSunshine (Mar 28, 2006)

no no. their organs are adapted to function in colder climates. I would assume that their heart rates are a tad slower then tropical fish.
I was saying the production of heat is why they cannot rapidly switch climates like for example people can. Much like reptiles. when cold climate comes on their bodys start to function slowly. But unlike reptiles fish can't really function or hibernate. So because they don't have that ablity rather then just taking a nap they suffer and eventually die. thats if the initial shock of climate change dosen't kill them right away. 
I would also guess that cold water fish would do better in tropical waters then tropicals in cold water.


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## acestro (Jul 7, 2003)

Your last statement is true for the most part, except some cold water species are used to higher oxygen levels (cold water holds more oxygen). But why tropicals cant tough out a winter the way natives do is still a tricky question.

My understanding is that there are some enzymes that keep cool water fishes from simply 'falling over' when it gets cold. But I still havent seen a good explanation. Good discussion so far though


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## MR.FREEZ (Jan 26, 2004)

i think , just my thought though, that it would have to

do with their red blood cells and how their blood carries

oxygen. fish in antarctica







have no red blood

cells cause the water is so rich in oxygen they dont

need them. tropical fish live in higher temp water

were oxygen could be very low, maybe i dont know

just one of those thing bouncing around in my head


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## flyboy (May 11, 2004)

Very interesting question. One of the big factors is that enzymes have a specific range of temperature that they operate at. Once that temp is breached, either too hot or too cold, the enzyme fails to function. Enzymes at low temperature operate too slowly to be efficient. And since enzymes are proteins, at high temps they denature, loose there 3-D shape and structure. In climates like Antartica, fish have stores of glycoproteins in the blood which act as an "Anti-freeze." That is a big factor as well. Since blood by volume is 55 percent plasma, and plasma is 90 percent water and water freezes. These ice crystals form in the blood and as you can imagine the results are horrific.

Freez, you are correct as to fish in Antartica have a special adaptaton within their blood, however they DO have erythrocytes (RBC's). It is hemoglobin, the iron-containing metalloprotien which transports oxygen, that they lack. This makes the blood thinner, which decreases the amount of force needed from the heart to push the blood through out the arteries, thus allowing their metabolism to be slower and conserve valuable energy.

On a side note, did you know mature Erythrocytes do not have a nucleus? They have one at first but then spit it out to acquire more room for more hemoglobin, and help the RBC to achieve the biconcave structure which is perfect for collecting oxygen. Our bodies are amazing, we fit together like a puzzle, each part complementing the other to sustain life.

Here is a link with some good info. Here


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## MR.FREEZ (Jan 26, 2004)

righton flyboy, i know there was more to it

for those fish in the "real deep south"









was a long time ago i saw that info somewere


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## flyboy (May 11, 2004)

Lol, yea. Living organisms have an amazing ability to adapt to their surroundings.


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## Polypterus (May 4, 2003)

Ace is this a trick question? Tropical or coldwater or temperate is a rather subjective term on the individual species level.

Temperature can directly affect a variety of functions (metabolism, physiology, etc.) in a specific species differently, Many of these internal functions are naturally selected for by the species through their interaction with the surrounding habitat and niche. Different localitites of the same species can also show varied Temperature preference depending on a variety of selection pressures. Some species have been shown to have Circadian ideal temperature preference.

It is very hard to pigeon hole this subject into a simple package as it is incredibly variable from species to species. There are many "tropical" fish that have Temperature preferences or tolorances to what many would call "Coldwater", Likewise there are "Coldwater" fish that can adapt to "Tropical" temperatures or that for some physiological function (I.E. Spawning) seek "Tropical" temperature ranges.


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## acestro (Jul 7, 2003)

Yeah, it is sort of a trick question. But I'm impressed at the discussion that is evolving.

The specificity of enzymes to temperature and pH was the first thing I had thought up, but I dont know if that's enough to explain it. I need to see if I can find any real work done with it.



flyboy said:


> On a side note, did you know mature Erythrocytes do not have a nucleus? They have one at first but then spit it out to acquire more room for more hemoglobin, and help the RBC to achieve the biconcave structure which is perfect for collecting oxygen. Our bodies are amazing, we fit together like a puzzle, each part complementing the other to sustain life.


While this is true for mammals, it is not true for other vertebrates. Most animals have nucleated blood cells, including birds from what I know.

Kinda weird actually :laugh:

Another cool thing to look into might be digestion and diet (of course we aren't going to find a silver bullet for this vague question). There are tons of algae eating fishes in the tropics (salt water) and they are conspicuously absent in the cooler areas (where you get algae dominated communities). Temperature may affect (again) enzymes for digestion, or just digestion in general.


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## flyboy (May 11, 2004)

Oh, I didn't realize that other vertebrates had nucleated RBC's. I have been mostly interested in Human anatomy and physiology and assumed this was true for most, if not all, vertebrates. That is very interesting that birds do not have this feature, especially since they have so many large muscles needed for flight which require a lot of energy.

Metabolic BioChemistry is very interesting. I have always been interested in proteins, including enzymes. One of the things I like learning about is how we regulate homeostasis through positive and negative feedback.


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## acestro (Jul 7, 2003)

flyboy said:


> Oh, I didn't realize that other vertebrates had nucleated RBC's. I have been mostly interested in Human anatomy and physiology and assumed this was true for most, if not all, vertebrates. That is very interesting that birds do not have this feature, especially since they have so many large muscles needed for flight which require a lot of energy.
> 
> *Metabolic BioChemistry is very interesting. I have always been interested in proteins, including enzymes. One of the things I like learning about is how we regulate homeostasis through positive and negative feedback.*


Good stuff.

Birds are reptiles essentially, they have more similarities to crocodilians than mammals.

Also, birds are a close second to mammals in oxygen efficiency. How can birds do so well with nucleated RBCs? I'd guess it's because their respiratory system may be the most efficient in the animal kingdom (air sacs with no stale air).


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