Fish, Water Temperature and Oxygen
Date: January 2008
Do fish breathe better in hot or cold water and why?
If a fish can get enough oxygen to live, then it can breathe well enough.
Having "more" oxygen isn't necessarily "better." There are fishes that live
in hot water, cold water, and everything in between. Some need a lot of
oxygen, some don't. Cold water can carry more oxygen, but that doesn't mean
it's better for fishes.
Even though "more" oxygen isn't necessarily "better", there are some factors
that affect how much oxygen is available to a fish, so I'll share a few more
First, is the maximum amount of oxygen that can dissolve in the water. For
both salt and fresh water, oxygen solubility (solubility is the word we use
for the maximum amount that can dissolve) increases in colder water. Hotter
water cannot hold as much oxygen as colder water. Having more oxygen in the
water may help a fish to breathe more. As a side note, this is considered
'weird' -- usually, hotter things dissolve better, but the opposite is true
for gases. Gases tend to dissolve more easily in liquids when they're cold,
but solids tend to dissolve more easily in liquids when they're hot.
Second, is the amount of oxygen that's actually in the water. At the
surface, air can exchange into water easily, and the water right at the
surface will be at (or close) to the maximum. However, as you go deeper, the
amount of oxygen decreases below the maximum. This is because fish or
chemical reactions in the water use the oxygen, or currents in the water
carry oxygen-rich water away and leave oxygen-poor water. All of these
factors can make a fish unable to get as much oxygen as it might need.
Third, are various biological factors such as how well-suited for various
temperatures a given fish is. Some fishes prefer cold water, while others
prefer warm. Some fishes actually do better in oxygen-poor water, while
others prefer oxygen-rich water. Also, various impurities in water can
prevent fishes from breathing -- for example, some kinds of chemicals bind
to gills and stop them from working. I am very much not a fish biology
expert, so I won't spend much time on this, but all of these can influence a
fish's ability to get as much oxygen as it needs.
So overall, the answer depends on the fish and where it is, but cold water
can hold more oxygen than hot water can.
Hope this helps,
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Update: June 2012