Single Cardinal Tetra has lump @ base of tail - please help

Hi, LLL. I'm so sorry your fish is having this problem. This could be a tumor, as you suggest, or it could be a bacterial infection. I have not, personally, had anything like this in any of my fish.

I did have a photo in my files that is somewhat... well maybe a little bit... similar that I will upload. It's hard to see the area well in your photo, and the red color of the Cardinal precludes easily seeing any redness in the area that might indicate infection.

Perhaps your own eye can see if the photo I provide here looks anything like your Cardinal's problem area.




This photo is from JBLonline, a company in Germany that has many products and services for aquaria, and they have a hospital section on their site that has many photos. This photo was reported to be a case of bacterial infection of the peduncle of this fish.

Do you see any similarities to your fish?

Indeed, the pic you found looks a lot more like yours. I didn't see that one on the JBL site.

The white-ish look in their picture is likely due to the scales standing away more than your Cardinal's are... or even some loss of scales in the pic from JBL.

Otherwise, your fish's lump looks strikingly like the JBL fish.

First prioity is to make sure your tank water is pristine. It's good you separated him form the others. Test your parameters with a good liquid test kit and make sure that ammonia and nitrite are at 0ppm, and nitrate around 20ppm.

A really good water conditioner is Prime, by Seachem. It will help with detoxifying ammonia, nitrite and nitrate, in addition to removing chlorine and chloramine in the water. Whatever is going on, he needs to have no traces of ammonia and nitrite in the water.

I had a technical rep from API tell me, the other day, that I needed to use Melafix and Pimafix for an infection that seems to be a skin or deeper tissue infection.

I was dumbfounded, because I thought he would suggest Furan 2, most likely, but he said, "Nope... I'd use Melafix and Pimafix." Well... you could try that first, along with pristine water, until you see more symptoms.

If you want to try more serious meds then I would go with Furan 2, which is a pretty broad spectrum antibiotic, it's absorbed through the skin, and should help with most bacterial pathogens that could be causing this.

Another is Maracyn 2, which is a broad spectrum antibiotic that is absorbed through the skin.

I hope this helps. Please keep us posted on his condition.

How long has this tank been set up?

YOu said 20 liters which is approximately 5 US gallons.

I usually dont criticize others on issue of overstocking but if you do have 5 cardianls and many guppies, it may be somewhat overstocked in 5G.

How is pH, NH3, NO2 in both 5 G and 1/2 gallon tanks before water change?

Check the pH/NH3/NO2 of tap if you are using tap to perform pwc.

DOnt know the situation with tap water in Singapore at your location. Hopefully no NH3/NO2 in tapwater however if pH is way off b/n tank and tap, would recomend very small but frequent water changes if such is required as unnecessary water changes can make the situation worse.

Post results of tests from both tanks/tap and we will go from there.

I didn't notice that tank size, but Cerianthus is right, your problem may have begun due to water quality issues in a tank that is over stocked. It's hard to keep small tanks stable, regarding the ammonia, nitrite, nitrate, ph, etc., especially when there's a heavy bioload.

I hope things improve for you. As Cerianthus stated, small frequent water changes will help conditions be healthier in the tank for your fishies. Fish have amazing recuperative powers when they are kept in really clean water.

Keep us posted.

It is possible that it is Penducle Disease.