When done correctly, venting can effectively allow those built-up gases to escape from the swim bladder, improving a fish's ability to swim back down to the depths from which it came – and increasing its chances of survival. ... This can cause further injury to the fish.

Should you vent a fish?

It is best to vent the fish as quickly as possible with a minimum of handling. If the fish's stomach is everted out of the fish's mouth, do not attempt to push it back into the fish's body. ... The fish's everted stomach should not be punctured.

When should you vent a fish?

If a fish appears to be normal (not bloated and able to swim down on its own) then venting is not necessary. To vent hold the fish gently but firmly on its right side and insert the venting tool at a 45 degree angle at the base of the pectoral fin.