Why do fish float upside down when they are dead?

Answer 1

While this is not always true, the reason this happens is that when the fish dies the gasses from the bacteria feeding on the now deceased fish begin the build up inside the fish, thus causing its belly to become lighter than the rest of its body and turning it upside down.

Answer 2

The poor thing is dying from poison in its water. My advice is do a water change ASAP. It is just possible the fish could recover. Then may I suggest that you follow the basic rules of fishkeeping if you want to be successfull at keeping fish. The rules are. :- 1 inch of fish needs a MINIMUM of 1 gallon of water. :- Every tank needs a permanently running cycled filter (to remove the ammonia). :- Every tank needs at least 50% of its water changed every week (to reduce the nitrate). Fail to follow one or all of the above and I can guarantee you will have constant health problems with your fish.

Answer 3

Fish have air bladders along their spine inside the body cavity. While it is true the fish could be dying, that isn't always the case. If the water is not well oxygenated the fish can't extract enough oxygen to keep the bladder full. this will create an unbalanced weight condition forcing the fish to roll upside down. Unless the fish can find more oxygenated water it will eventually die. If a fish is in an aquarium, be sure the oxygen pump is operating properly, or move them immediately to clean, fresh, water. This can save them.