My betta fish has a small ball on its bottom fin. What is it?

Thanks for reaching out about Spike and including a photo. It is difficult to visualized the lump on the picture but if water quality is pristine, a veterinary visit might be in order to assess. Bumps/lumps can be parasites, infections, enlarged internal organs and more. Monitor appetite. Containers of food should be re-purchased every -23 months as vitamin C degrades quickly and fish has a nutritional requirement for vitamin C. If not a new fish (owned for several months or more), unlikely to be parasitic problem. Good luck.

This is difficult to determine exactly from the picture you posted. There seems to be a mild swelling which could be completely normal at this stage (especially if not other signs are present). Please complete your question adding other pictures (one from above would be quite helpful) and describing if other signs are present or not to receive more answers from us.

Without an image or exam, it is difficult to say with any certainty what the lump may be. Infection or injury would be likely culprits. If he has anything sharp in his bowl, remove it. Check the water quality and chemistry as poor water quality can predispose him to infection. Use a home test kit or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Aim for 0 ppm ammonia and nitrites with a nitrate level of 20 ppm or less. Partial water changes can be done to stabilize chemistry and improve water quality. Use only aged or conditioned water that is temperature matched to prevent stress or shock. Bettas do best between 78 F and 80 F. Change no more than 30% total volume at one time. You can try using plain aquarium salt (NOT table or Epsom salt) as a general tonic. It can treat minor infection and helps aid in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup of tank water and gently pour it into the tank. Treat for 10-14 days then reassess his condition. Perform water changes afterwards to reduce salinity. Do not use salt for more than 14 days in a row. If there is no change, a broad spectrum antibiotic can be found in the Aquarium section of the local Petco. Follow label directions carefully and remove the carbon filter insert during treatment if indicated.

Thanks for reaching out about your fish and including a photo. This is a fairly large lesion and needs to be diagnosed and treated. Parasitic infestations and bacterial infections must be considered. Adding non-iodized salt at 1 tablespoon per 5 gallons for 3 consecutive days might provide some osmotic relief but is not therapeutic levels. A skin scrape and microscopic examination is needed to diagnose parasites is needed. Different parasites require different medications. Bacterial infections should be treated with systemic antibiotics through injections or oral medications, not water additives. Good luck.

Thanks for reaching out about Kai and including photos. This could be a solitary Ich lesion (which is unusual, as there are usually multiple) or a hyper-active mucous gland. Check water parameters for pH, ammonia, nitrites and nitrates, correcting any problems. If more lesions appear, a veterinary visit can help with a diagnosis through a microscopic examination of a skin scrape, and therefore prescribe the appropriate treatment. Good luck.

It may be a tumor or infection since it is just on one side. Without diagnostics though, it can be difficult to determine the underlying cause. Maintain pristine water quality via filtration and regular partial water changes. You can try a broad spectrum antibiotic which can be found in the aquarium section of the local Petco. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. If antibiotics to not resolve the lump, then it could be a tumor or mass which would need to be addressed by a veterinarian experienced in treating aquatics.

Thank you for your question about your goldfish. I see the area that you are referring to in the photo, but it is a bit blurry so I can't see it completely clearly. If you feel that your fish is otherwise doing well - it is staying upright and balanced, it is eating well, the two fish aren't fighting, and it is swimming normally, then I would recommend to monitor for the time being. If any of this changes, then I would recommend taking your fish to a veterinarian who is familiar with fish. You can use the AAFV website to help identify one in your area if you don't know of any. Also, you can contact veterinarians in your area who see other zoological companion animals (such as ferrets, birds, and reptiles) and they, or someone they know, may also be able to examine your fish. I hope this gives you a place to start, and thanks for using Petco Pet Education Center, formerly Petcoach.