Water: Deprived of Oxygen, killing fish?

[dant]

How can there be no oxygen in water!?

In other words, water is chemically: H2O - and being deprived
of oxygen, means there is only H2 left, ergo, no water?

Can someone explain?

 

[mkrnhr]

Hello dant,
I do not recall chemistry courses from middle school. But the fish do not "breath" the oxygen from H2O molecules. They breath the O2 molecules that are dissolved in water.
Pure water is only H2O molecules, but in "normal" water, you have water H20 molecules, O2 molecules, CO2 molecules, and many others.

 

[dant]

As I understand it, water needs to be oxygenated (replenished)
by churning air (oxygen) with water, otherwise oxygen would
bleed itself out of the water and return to the atmosphere.

So perhaps the water in the harbours are not oxigenated enough
to support the fish ecosystem, they are basically death traps.

On the other hand, the water could be polluted, interfering with
their sensitive bio-systems, also leading to their deaths.

I guess I can understand what is meant by "oxygen deprivation"
and it could take many forms, two as listed above.

 

[flashgordonv]

I used to keep freshwater fish in an Aquarium. One of the key things I needed to do was make sure the filter returns agitated the water at the surface so there was a constant interchange and replenishment of oxygen in the water. Early in my fish-keeping career, I accidentally changed the water flow so it vented under the surface, and I lost the entire tank of fish overnight.