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Bubble on side of fin, blood.

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  • Regular Member

On of my tropical fish (danios) has a large clear bubble on its fin, there is also blood around the bubble. The water is still clear, the other fish seem fine as well.

It does look quite bad, I have already lost one of the fish after it jumped out of the tank via the small space in the back for cables. Could anyone offer advice on how this (what ever it is) could be treated. I have added a link to a video below of the fish:


Many Thanks.

  • Test Results for the Following:
    • I have not tested.
    • Other Required Info:
      • * Brand of test-kit used and whether strips or drops?
      • * Water temperature?
      • * Tank size (how many gals.) and how long has it been running? 28 Gallons 6 Months
      • * What is the name and "size of the filter"(s)?
      • * How often do you change the water and how much? 1 Month
  • * How many days ago was the last water change and how much did you change? 3 weeks.
  • * How many fish in the tank and their size? 3, small.
  • * What kind of water additives or conditioners? Tap water treatment
  • * What do you feed your fish and how often? Flakes
  • * Any new fish added to the tank?No
  • * Any medications added to the tank?No
  • * Any unusual findings on the fish such as "grains of salt," bloody streaks, frayed fins or fungus? See above
  • * Any unusual behavior like staying at the bottom, not eating, etc.? all hovering at the top.
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  • Regular Member


Even though the tank is very understocked with 28 gallons, you need to be doing weekly to fortnightly water changes to prevent a build up of bad bacteria. Fish usually will only jump if there's something wrong with their environment.

Is the tank heated and filtered?

Can you get your water tested by your local fish shop? They'll usually do this for free. Make sure to also take in a tap water sample and have that tested.

Once you know your parameters, it will be important to quarantine your sick danio. The blister might eventually pop, which is a potential risk to the other fish

Edited by Narny105
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  • Regular Member

Thanks for the reply, the tank is filtered, but not heated.

I have had a closer look and it does not appear to be a bubble, the fin and area under the eye look red raw.

I have changed the water and placed the sick danio in its own container for now. He seems to be ok.

Edited by Ronnie_1990
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Guest Mr Grump

Please complete the info form, this could easily be toxins.

Any fish keeper needs a test kit, get the API one from your local shop. We need at the minimum your Ammonia, Nitrite, Nitrate & pH levels as well as the tank temperature. Water changes need to be 20% once a week at the minimum. Is the tank cycled? Which product do you use to treat the tap water? What sort of filter do you have?

In the meantime, I strongly suggest that you carry out a 50% water change, treating the water with Seachem Prime as directed on the bottle. Do the water tests as a matter of urgency.

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  • Regular Member

I have changed the water around 70%, but unfortunately the fish with the large red patch on its fins has died. It seemed to be ok swimming around, but it just suddenly stopped. It has not turned sideways, could this indicate gas in its system? The other two fish appear fine as well but I am now worried they could get the same condition. Does anyone know what it could of been?

I am going to order a test kit and will do it as soon as it arrives.

Thanks for the help so far.

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  • Regular Member

You'll need a heater just to maintain it at around 24-25C

Since you're unsure of your pH, restrict water changes to a smaller ammount until you're able to test. A big pH swing can be just as stressful. Until it arrives, I would be doing daily 20% changes.

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