neon tetra

Why Is My Neon Tetras Mouth Open?

Your neon tetras will often open their mouths and breathe more rapidly. This is something that makes every aquarium owner worry about his/her neon tetras. But why do they do it? That’s what we’ll be looking at in this article. So let’s get started with all the possible reasons why your neon tetras mouth is open.

1- Sign Of Stress

It can be a sign of stress, Generally, Under stress, they will open their mouths very widely. This is a sign that they are in distress and should be removed from the aquarium as soon as possible.

If you have a community tank with other fish, then it is likely that your neon tetras have been bullied by another fish or some other creature like a snail or shrimp. If this happens, you should remove the aggressor or move them to another aquarium where they can be happy again.

Neon tetras mouth open is also a sign of illness in these fish so if you notice your neon tetra opening its mouth widely and constantly, then you should take it out of the water immediately and put it in a quarantine tank where it can rest until its health improves.

2- Sign Of Aggression

Neon Tetras betta fish companions

If you have more than one neon tetra in a tank, they can become aggressive towards each other. They will be constantly fighting and chasing each other around the tank. This can cause them to open their mouths wide as a sign of aggression.

3- High Nitrate Level

If you have a high level of nitrates in your tank, then the water can become oxygen-depleted. This is especially true for aquariums with live plants that use up much of the available oxygen in the tank. The fish may also be suffering from swim bladder disease or another illness that causes them to gasp for air at the water’s surface.

4- Due To Dehydration

One reason why neon tetras might keep their mouths open is that they are dehydrated. If you notice that your fish’s gills look “floppy” or that he has difficulty swimming for more than a few seconds at a time without stopping, then you should immediately check his water parameters to make sure that it isn’t too high or low for him to survive in it comfortably. If his water parameters are fine, then it’s likely that he just needs some extra water added to his tank so he can drink some more out of it until he feels better again!

5- Poor Nutritional Food

A poor nutritional diet can cause a neon tetra’s mouth to open. This is due to the fact that they are carnivores and need to eat meaty foods. If they do not have enough protein or vitamins in their diet, they will be unable to keep their mouth shut properly.

6- Sign Of An Infection

Neon tetras are very susceptible to infections and parasites, which can cause them to open their mouths for extended periods of time. If your fish has an infection or parasite in its mouth, you can use aquarium salt and medicine from your local pet store to help treat it effectively.

7- Water Is Too Hot Or Cold

The neon tetra needs to live in a tank where the water temperature is between 73 and 77 degrees Fahrenheit (23 to 25 Celsius). If the water is too cold, the fish may gasp for air at the surface of the tank or open its mouth wide in an attempt to get more oxygen. Neon tetras also like to live with other species of fish that are compatible with them, such as guppies or mollies. The best way to prevent this problem is to make sure your tank has good filtration and aeration to keep it clean and healthy for all living creatures that inhabit it!

8- High Salinity In Water

why are my neon tetras fighting

If your fish’s mouth is open, it could be a sign of high salinity in the water. Neon tetras are salt-tolerant and can live in brackish water, but not if the salinity is too high. You can acclimate the neon tetras to lower salinity by putting them in a bucket of tank water for 24 hours, then adding that bucket to their tank. Do this several times until you’ve reached the desired salinity level.

When Should You Be Worried?

If you are unsure if your fish is in distress or not, observe her behavior closely. If she is swimming around normally, eating, and acting like herself, then you can stop worrying about her. However, if she has been gasping for several hours and does not seem to be recovering from the stress of her environment (for example added movement from a new aquarium or sudden temperature change), don’t hesitate to act!


Because of their small size and tender breeding requirements, neon tetras can be a challenging fish to keep. If you regularly observe your fish exhibiting this mouth-open behavior, it is likely that one or more factors in the tank are stressing them out. It could be something as simple as an increase in light intensity or maybe an infection that has added stress to the tank. It’s always better to get help from your pet store.