With the help of oxygen cylinders and masks.

No

Fish breathe underwater using the oxygen that is dissolved in water.

So, do they use a mini vacuum cleaner to absorb oxygen from water?

No.

To absorb oxygen from water, fish use special organs called gills.

Gills are full of blood vessels.

Also, the walls of the gills and blood vessels are very thin.

Now, during breathing.

Fish take in water through their mouth and forcefully push it through their gills.

When the water moves through the gills.

The dissolved oxygen from the water passes through the thin walls of gills and blood vessels, and enters the blood.

Apart from this, the waste carbon dioxide present in the blood passes into the water.

Thus helping fish to breathe underwater.

Eventually, the carbon dioxide-rich water is given out from gills.