Raphael Catfish - white bubble

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Sep 20, 2023
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I woke this morning to see a white bubble/blister had appeared between the dorsal fin and body of my catfish. Not sure how long it's been there or if it's just appeared. I generally check the tank everyday just to do a head count and make sure there is nothing wrong but the catfish is generally hiding in one of the darker decorations and very rarely swims out into the main tank. When trying to get a photo of the "bubble/blister", the fish swam out quickly and it burst. Anyone have any idea what it is and if there is any immediate danger to the fish?

The tank is cycled and cleaned on average once every month. It's been a stable tank now for 3 - 4 years and the catfish has been a part of the tank since the very beginning. (I inherited the tank with the catfish already in it). It's a communal tank with 4 other plecos, 5 Corydoras, a school of Xray Tetras, 2 Clown loaches and a few juvenile Angel fish.

Any help would be greatly appreciated.


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Is the bubble (or remains of it) still attached to the catfish?

What colour was the stuff that came out of the bubble when it burst?

Did the fish do anything (rub against something that made it pop?

How did the fish respond when it popped?

Can you try to get a few more picture of it?
Is the bubble (or remains of it) still attached to the catfish?

What colour was the stuff that came out of the bubble when it burst?

Did the fish do anything (rub against something that made it pop?

How did the fish respond when it popped?

Can you try to get a few more picture of it?
Hi Colin,

The "bubble" burst as the catfish swam out from his hiding place and grazed off the log that is in the center of the tank. It happened so quickly and I didn't notice anything come out of the bubble when it burst. Looking at the catfish now, he's behaving normally (as in he's hiding and sleeps most of the day), but the blister has reappeared. When it initially burst it looked list a blister burst on your hand.

He's being stubborn about being photographed. I've done a 50% water change and cleaned out the filters today just to try and help keep the tank as clean as possible as it was due one anyway.

You can see from the photos the size of the blister and the coloration.


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Just to add....none of the other fish in the tank are showing any signs of disease or injury.
It's not a contagious disease. I'm going with a cyst. There's not much you can do about them short of surgery and most fish die under the anesthetic. You can try tying some fine thread around the base of it (where it joins the body) and hope the thread cuts the blood supply off. Then it should fall off and hopefully not grow back. You might have to tighten the thread after a week or so. The hardest part is holding the fish while tying the thread and hoping the balloon doesn't deflate or pop when you do it.
not going to dispute anything Colin says, but could it be some sort of parasite ( like hole in the head ) that is causing a weeping wound, that's filling a layer of skin???
It's not hole in the head. That's most commonly seen in cichlids kept in dirty tanks and has white worm like things sticking out of the skin around the head and face for a few days before they disappear and then small pits appear in the skin.
I did initially think it was some sort of parasite myself but surely something else in the tank would be starting to show signs of it too?? Having been watching it over the last 48 hours or so it does seem to be more like a cist. I thought a cist was a bit harder than this appears to be however. This is more like a large blister that's formed. I'll continue to monitor and may try the thread on it but considering how easily it burst yesterday I don't fancy my chances trying to hold this fish and not pop it again! 🤦‍♂️

Would it be an idea to seperate the fish from the rest of tank or do we reckon it'll be ok in it's usual habitat?

Thanks for the help guys!
Any chance it got poked… maybe another catfish barb???
It should be ok where it is. You can do bigger more frequent water changes and gravel cleans to reduce anything that might be in the tank, but it's most likely something that will only affect that fish.
He's the only catfish in the tank so he's pretty much left alone. He's the biggest guy in the tank so no one goes near him.

Looks like it burst again during the night but the fish seems unaffected by it. It also looks a bit cleaner and better today. He definitely needs to go on a diet though. 😂

Thanks for all the help guys. I'll monitor it but maybe it was just an injury he caused himself from getting too fat to fit into his usual hiding place.
Injuries don't cause blisters/ balloons to grow like that.

Monitor the site for infection because if it keeps popping it might develop a fungal or bacterial infection. Fungus will usually appear as white fluffy stuff around the wound. Bacterial infections show up as red areas in and around the wound. Salt can treat both if caught early.

You could add salt for a couple of weeks starting now and see if it helps.


You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

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