Sleep in fish, as in other marine animals, is a little-known phenomenon that is difficult to measure. However, as for humans, sleep is vital for animals, including fish.
Do fish sleep upside down?
Chances are you have noticed your fish sleeping upside down, however, it is not sleeping, it is in fact a disease called swim bladder disorder, it is quite simple to recognize when a fish is affected:
The diseased fish affected by swim bladder disorder loses total control of its swimming, floats on the surface or on the contrary sinks by swimming to the bottom. It may also regularly swim on its side and turn rapidly in an attempt to move.
How do fish sleep?
The fishes immobilize themselves between two waters, on the bottom or in the sediment, at night or during the day (depending on whether they are diurnal or nocturnal). Some even put on their pyjamas by changing color or by secreting a mucus envelope.
So yes, fish sleep, but in a different way than mammals. Moreover, they do not close their eyes and do not dream. In fact, they have no eyelids and no signs of a state similar to REM sleep, where dreams occur, have been detected in these organisms.
Why is your fish upside down (or on its side)
The causes can be many and varied. It can come from an injury following an attack, a shock, a pinch, … It can also occur by inbreeding or by selection for malformations For these reasons, Japanese goldfish, mollies balloon etc… are generally affected. Indeed, at a certain stage of their growth, the swim bladder does not develop properly and is compressed by other organs.
For the same reasons, the disease can also occur as a result of growth disorders in a small bed or an overcrowded aquarium. It should be noted that pollution can also affect the growth of a fish.
An internal tumor located on the swim bladder or on a nearby organ can also be the cause: various internal infections, viruses, bacteria, intestinal worms, … Indeed, a serious infestation can exert a pressure on the organs or damage them.
Finally, a strong constipation can also oppress the swim bladder.
What are the consequences of a fish that is upside down?
Whatever the cause of the swim bladder disorder, the effects are always the same. The fish, not being able to move properly, may not succeed in feeding, in integrating itself into its group (if gregarious), … and may die from this situation (inanition, cardiac arrest, killing by its fellow fish, …), especially if the disorders are permanent following a tumor, a serious injury, …
These disorders can also be temporary in the case of a light constipation.
How to treat your fish for swim bladder disorders?
Depending on the cause, a treatment can be considered. For bacterial infections, worm infestations or constipation, there are many specific treatments on the market. In the case of wounds, they can heal and the disorder can then disappear.
In the case of long term disorders due to tumors, severe growth disorders, genetic defects… the disease is unfortunately incurable.
When the first symptoms are identified, the fish can always be isolated in a hospital tank for a supply of fresh vegetable food (boiled vegetables) accompanied by an increase in temperature and a good maintenance (hygiene) which can sometimes overcome this disease.
In the case where the disease is considered incurable, some aquarists, after reflection and common sense, may decide to euthanize the fish before it inevitably dies by itself. Note that a fish that can swim, even with difficulty, will be able to live more or less normally. On the other hand, a very affected fish may suffer, sometimes for several months, before dying.