Hmmmmmm, again, this is an interesting issue too.
My experience with
fish and temperature changes has been both good and
bad. First, I
should note that I change my water directly from the
tap and check the
temperature coming from the tap by fingertip (yeah,
Mr Engineer uses his
fingers, good to plus or minus ~3 degrees). Second
I should mention I
check my temperature to the Celsius scale (only
because that is the type
of thermometers I have). Third I will mention that
I have fish from
Asia, Africa and South America mixed in most of my
tanks (Ack!! How can
that be??)
Soooo, ok, stick to the question please. Fish and
Temperature. Oh
yeah. Let's look at an example a little closer to
home to see if we can
draw some possible parallels to the aquatic world.
How about people?
You, me, the kid next door....perhaps the kid next
door is the best
example, or, even my own kids. Kids do not wear
coats.....simple fact.
I don't care what the temperature is outside, they
do not wear
coats....unless forced to do so. Do kids get sick
every time they go
out the door? Nope. Can they go out in hot weather
without a coat and
suffer no ill effects? Sure. How about warm
weather? Absolutely. Ok,
let's get to the cold weather level? Sure, they can
play in cold
weather without a coat and do fine too. Freezing
weather? Yep, this
works too. Seen it with my own eyes. Annnnnnnnnnd,
I am sure if most
of us think back to our childhoods (which for me is
a bit of a
challenge) we will remember times when we played
outside in the cold
without coats too and suffered no ill effects. The
key is the amount of
exposure to the outside temperature and health of
the individual when
temperature change occurs from what I have seen.
For instance......kids playing outside in 40 F
degree weather, without a
coat, can go for hours with no significant impact,
except rosy cheeks
perhaps. Go to temperatures below freezing and now
it is a matter of
how long the extremities (fingers, toes and nose)
can handle the cold
before the initial effects (burning sensation) of
frostbite set in.
Yet, even when we begin to feel the first stages of
frostbite it does
not mean that one will become sick from it. It's
amazing how well a
person can adapt to temperature changes from about
25 F to 100+ F with
no ill effects.
Now, let's expose that same person to a cold or flu
virus or bacteria
and do the same thing. Seems that the person is
more apt to becoming
ill as a result. The temperature change is an added
stress (your body
will try to maintain its set temperature) on the
body's system that
makes it easier for the virus or bacteria to
overwhelm the body's
defense systems. The interesting part of this is,
temperature change
will not make you ill initially, but, it can lower
your body's ability
to defend itself against viruses or bacteria.
Soooo, looking at this example, one would think that
if fish are like us
to some small extent they should be able to handle
temperature changes.
And, from my experience, they do.
Ok, but, fish are not warm blooded(Endotherms, like
us). Fish are cold
blooded(ectotherms) Well, this is true. Yet, can
cold blood and warm
blood make that much of a difference in temperature
tolerances?
Warm-blooded creatures, like mammals and birds, try
to keep the inside
of their bodies at a constant temperature. They do
this by generating
their own heat when they are in a cooler
environment, and by cooling
themselves when they are in a hotter environment. To
generate heat,
warm-blooded animals convert the food that they eat
into energy.
Cold-blooded creatures take on the temperature of
their surroundings.
They are hot when their environment is hot and cold
when their
environment is cold. In hot environments,
cold-blooded animals can have
blood that is much warmer than warm-blooded animals.
Cold-blooded
animals are much more active in warm environments
and are very sluggish
in cold environments. This is because their muscle
activity depends on
chemical reactions which run quickly when it is hot
and slowly when it
is cold. A cold-blooded animal can convert much more
of its food into
body mass compared with a warm-blooded animal.
What does this mean? Something interesting happens
here. A
disadvantage to being warm-blooded is that
warm-blooded bodies provide a
nice warm environment for viruses, bacteria and
parasites to live in.
Mammals and birds tend to have more problems with
these infections than
do reptiles and fish, whose constantly changing body
temperatures make
life more difficult for these invaders. However, an
advantage of this is
that mammals and birds have developed a stronger
immune system than
cold-blooded animals.
A cold blooded reptile or fish immune system is more
efficient when the
animal is warmer. This can be seen when treating
fish for ick. The
first thing that helps is to elevate the tank
temperature. This forces
the bacteria to replicate faster, but, it also
offers the fishes immune
system a chance to go into high gear to fight
infection too. However,
since bacteria probably grow more slowly in lower
temperatures, cold
blooded animals sometimes intentionally lower their
body temperatures
when they have an infection. This is proven out in
studies of disease
control in axolotls. Diseased axolotls can be
placed in a refrigerater
and cooled to near freezing and they seem to heal
quicker than if left
at higher temperatures. So, you can see cold
blooded animals walk a
thin line as to which is better, cooler temperatures
or warmer ones.
The key to the fish and axolotl temperature impact
is the duration of
the temperature (Hmmmm, sounds like my kids again).
Axolotls kept as
near freezing do not eat. How long can they go
without eating? Long
enough to fight off an infection if they are in
reasonable
condition.....but, not for significantly long
durations. How long can a
fish go at elevated temperature? Long enough to
allow ick medication to
kill off the parasite, but, they cannot live at
elevated temperatures
near as long as they can at cooler temperatures.
Ok Clay, what is the point of all this? In short,
the health of the
subject and duration of the temperature change are
the keys to the
potential adverse impact of environmental
temperature variance to the
subject. Temperature fluctuations over short
periods of time (swimming
through thermoclines) can be accommodated by fish
with no adverse
impact. This is only true provided the fish are
healthy to begin with.
If a fish is diseased, temperature fluctuations can
either improve or
degrade the subject's condition. Without trial and
error, I am not sure
if it can be predicted which way the diseased
subject will sway when the