What's that lump?

  • #1
Hi there - I'm new to this forum, but am here because my daughter's betta fish has a mass that has been growing on its top fin for the last couple of months. It started out quite small on one side of the fin and now is much larger and is visible on both sides. There are no other lumps that we can see. I've done a bunch of online research to try to figure out what it is, but the best I can come up with is cancer. I'm hoping someone here with more fish knowledge can either confirm that or identify what else it might be. Thanks so much for any help!

FYI - He is the only fish in our tank; everything else about him is fine; he eats, his water quality is great, no other issues except that he used to be a tail biter and occasionally we notice that he's bitten off a little chunk; he is about 8 months old.
Also, please ignore his strange coloring, the photo was taken through a bend in his tank so it shaded him strangely.


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  • #2
Honestly I have never seen anything like that! Are those enlarged scales? A few more photos would be great- from a few different angles. Also some answers to some routine questions would help- tank size, water parameters ( pH, ammonia, nitrites, nitrates, temperature), water change schedule, and history of new tank additions (I know he is the only fish but include plants and inverts. I will try to do a little sleuthing on skin tumors.
  • Thread Starter
  • #4
Thanks for the reply!

I've added some more photos. The first 2 are from about a month ago. The others are from today. I find it incredibly difficult to get clear photos of this guy! I don't think they're enlarged scales, but it does look like it sometimes. The lumps look so different depending on the lighting. They started off whitish and over time seem to have changed to be mostly dark.

You can see in a couple of the photos that the lump is on both sides of the fin. It started on his right side and then seemed to spread to his left side (through the fin), now it is basically equal on both sides.

It does look a lot like the photo of the chromatophoroma that you linked. Maybe we've got the second case! LOL

Our tank size is 3.5 L. We do a 1/3 water change every week and a clean off of plants, etc. about every 3 weeks as we do get a little bit of algae. Nothing new in the tank - it's just him with silk and plastic plants and a little house. The water parameters are all within ideal range, we check it regularly and adjust when necessary. His tank temperature might be a little low, currently sitting at 77F. Our heater doesn't seem to want to heat it up as much as we'd like. We add bacteria with each water change. We have a small bag of crushed aquarium coral in his filter area to help with KH as ours is naturally really low.

Thanks for your help!!


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  • #5
Huh. It doesnt look like a parasite to me but could be an abscess I suppose. I am thinking it is most likely a tumor. Is he 8 months old or have you had him 8 months? Bettas at most shops are 6-12 months old at purchase. If he is 8 months old, he seems a bit young for tumors but if you have had him 8 months he may be middle- aged or older. If you have the resources you may want to take him to an aquatic vet. He looks healthy enough for anesthesia and the tumor does not look internal. Heck, if you live near a vet school they may even give you a discount if they can biopsy it and publish results in a journal!
fishvets.org | Find a Fish Vet | American Association of Fish Veterinarians
Fishlore has a list of aquatic vets too:
A HUGE list of aquatic vets Important - | 63797 | Freshwater Fish Disease and Fish Health
Good luck! I will let you know if I think of anything else!
  • Thread Starter
  • #6
Yah, abscess was the other option that I came up with as well. We've had him for 8 months, so I guess I have no idea how old he really is. Pretty sure he's grown a bunch since we got him, so he couldn't have been full grown at the time. Thanks for the links, however, I'm in Vancouver, BC, so those vets won't work for me. I have a note in to my usual vet to see if they'll examine a fish. I'm guessing there's not much they could do, but I'm really curious as to what it is!
Also, his tank is 3.5 gallons, not litres. It's not huge, but we are not cruel. LOL

Thanks for all your help.

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