I have a fish bowl and they are all swimming with their mouth touching the water surface, almost always.

  • Are they hungry?
  • Do they suffer from insufficient oxygen concentration in water?
  • Is the water dirty?
  • Any other possible problem?

Swimming: mouth touching the water surface


The bowl is a sphere of maybe 1 foot in diameter. There is no filter or pump. No equipment. I change water, more than 50%, each morning. I keep new water overnight inside a separate container, before changing. I feed twice a day, each time maybe 10x grains of fish food.

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    Welcome to pets.SE! Please add information about: The size of the bowl, the water changes you do or equipment (filter, pump) you use and which result a water test give (nitrite nitrate ammonia...) until now it could be all, from less oxigen, to toxination... Commented Mar 26, 2021 at 5:31
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    you should read this fishlore.com/NitrogenCycle.htm and get a real fishtank with filtration and heating,those round fishbowls will never get the biological balance right.starting a new tank takes time often from 1 week to over a month. Commented Mar 26, 2021 at 6:19
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    Please read this. Those typical round goldfish bowls are much too small even for a single fish, not to mention several. It should be illegal to sell them, because they always lead to animal cruelty. But since the image of those bowls was and still is perpetuated by media. people ask for them and many pet shops care only for the money, not the wellbeing of the living and feeling creatures they sell.
    – Elmy
    Commented Mar 26, 2021 at 6:41
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    Related: pets.stackexchange.com/questions/19656/…
    – SerenaT
    Commented Mar 26, 2021 at 10:18

1 Answer 1


Fish swimming with their mouth constantly glued to water surface is a sign that they are gasping for breath. However, the reason for them being short for breath usually isn't the low oxygen concentration in the water itself, but toxic effect of water pollutants: ammonia (NH3), which burns fish's gills and disables them from extracting oxygen from the water; and nitrite (NO2-), which binds to hemoglobin in fish's blood, blocks oxygen from being transported to all the tissue, and causes generalized hypoxia.

Nitrite poisoning could be recognized by looking at the color of fish's gills - healthy gills are bright red, while nitrite poisoning makes them tan-brown.

If the bowl has diameter of around 1 foot, then - considering its shape visible on the photo - it has the volume of less than 10 liters and this is extremely small. In case of goldfish, there should optimally be at least 20 gallons (around 76 liters) of water volume for one goldfish and 10 gallon (around 38 liters) for each additional beyond one. Goldfish are exceptionally dirty and have a high bio-load, which means they require a large amount of water to safely dilute their excreted waste before it gets neutralized by the filtration system.

Having a functional filter in the aquarium is essential, so please install it as soon and possible.

Please also read about nitrogen cycle in the aquarium - it takes around a month to cultivate the essential bacterial flora in the filter to enable the filter to safely neutralize the waste generated by animals and decomposing matter in the aquarium.

Also, holding water overnight doesn't necessarily make it appropriate for aquarium use because some tap water facilities sanitize it with chloramine instead of chlorine. Chloramine is synthesized in water by treating it with both ammonia and chlorine. Chloramine isn't volatile enough to diffuse out into the air as fast as chlorine and it could take well over a few weeks for it to do so. It is a lot safer and more convenient to use a water conditioner from pet shop - it doesn't need to be a fancy nor expensive one, just please make sure it says "neutralizes chlorine and chloramine" on the label. Both chlorine and chloramine could also burn fish's gills and cause them to gasp for breath at the water surface.

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    Additionally, some water facilities will add ammonia in the treatment process--using a good dechlorinator can take that out of the water, too.
    – Allison C
    Commented Mar 26, 2021 at 13:50
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    @AllisonC Hi thanks for comment and upvote, yes you are correct but this information is already indirectly present in the answer because chloramine is what is present in the water treated with both ammonia and chlorine, and as far as I understand if a water conditioner's label says "neutralizes both chlorine and chloramine" then it implicitly says that it neutralizes ammonia as well. Chloramination article. I don't know what is the chemical mechanism of neutralizing ammonia and I don't know whether it is permanent, as far as I know it ...
    – lila
    Commented Mar 26, 2021 at 14:26
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    @AllisonC ... neutralizes ammonia by converting it to the practically-harmless ionized form (ammonium) and temporarily stabilizes it in this form, but nonetheless it is reversible; I remember reading many times that it only neutralizes ammonia for about 24 hours. One the other hand, chlorine is neutralized permanently because free chlorine is reduced to harmless chloride ions which are highly stable and cannot spontaneously reverse back to free chlorine.
    – lila
    Commented Mar 26, 2021 at 14:30
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    Right, I'm just making a note for explicitness/clarity :)
    – Allison C
    Commented Mar 26, 2021 at 14:34

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