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10.3.4. Fin Rot

10.3.4. Fin Rot in Aquarium Fish
10.3.4. Fin Rot in Aquarium Fish

Fin rot is when the fins of a fish start eroding. Typically the eroding fins will have white edges. If white edges aren’t present it could be fin nipping and aggression which has caused the problem.

3 photos of fin rot in fish
3 photos of fin rot in fish

This is most often gram-negative bacteria (columnaris, aeromonas, etc.).

Treatment

Fin rot should be treated with broad spectrum antibiotics (Thomas Labs Fish Mox, Midland Vet Service Aqua-Mox, VetDepot Amoxicillin, Fishbiotic Ampicillin, Mardel Maracyn 2, SeaChem KanaPlex, Thomas Labs Fish Min, API Fin And Body Cure and Thomas Labs Fish Doxy). These antibiotics ONLY work when mixed into the food. They do NOT work when put into the water of the aquarium.

These medications are only available over the internet. Fish stores have all gone over to “natural” medications which have a very high profit margin.

It is easy to make medicated food. Heat 1/4 cup water (two ounces or 58 milliliters, not a lot) in the microwave. Then blend one 1/4 ounce of plain animal derived gelatin (Knox gelatin, one envelope) into the hot water with vigorous stirring. Take two tablespoons of dry commercial fish food (pellets or flake) and mix it with just a little of the hot water/ gelatin mixture. Add hot water/gelatin until you get a paste like consistency. If it gets too watery just add more food.

Fin rot
Fin rot

Then add just a “smidgen” (roughly 1/16 teaspoon, a 1% to 2% addition) of medication to the mud. If you are using more than one medication mix the medications together, then use just a “smidgen” of the mixture. If you are using a packet of medication, take just a “smidgen” of the packet contents. Mix and mash the whole mass thoroughly. Spread it out into a pancake about 1/8th inch (3 mm) thick on a plastic film or a plate. Then put in the refrigerator. If you plan on keeping it for more than two weeks put it in a small plastic bag and freeze.

All the fish in the aquarium should be fed a steady diet of the antibiotic laced food for at least ten days. Note that the exact amount of medication which goes into the food is not very important. Antibiotics can be overdosed pretty much with abandon as they are only toxic in large doses over a period of months.

Note antibiotics in the food do not affect the filters so they can be left in place and operating.

If you can’t resist the urge to treat the water, remove the biofiltration media (including sponge and/or foam) in the filters and put it in an open container for the duration of the treatment. Sometimes antibiotics kill the beneficial bacteria and sometimes they don’t. In any case the filter media will denature the antibiotics. Monitor the ammonia and would do a 50% water change if it spikes above 1 ppm. Reduce the amount of food fed by 2/3 rds.

Note that if antibiotics are not available (i.e. in Europe or Canada), it is quite easy to take a pill or capsule of human antibiotic and use it for fish. If it is a pill just grind it up. Just be aware that the human antibiotics are about ten times more potent than the aquarium antibiotics, so just a “smidgen” in the food is more than enough. This is a very good option for the folks in Europe or Canada, where fish antibiotics are illegal.

Fin rot on a Goldfish
Fin rot on a Goldfish

If one has more than one fish with a bacterial disease, one must treat the whole aquarium. This is an emergency. Don’t fool around with herbs, tree leaf oils or some ineffective treatment. Ben Ochart treated a bacterial infection with Pimafix and Melafix. They did nothing to stop the infection. He lost a lot of large beautiful fish before he stopped the infection with antibiotics. This link covers the snake oil medications such as Melafix and Pimafix:

12.4.1. Natural Medications

It is very common when fin rot presents itself to also have a grey colored organism on the fish which looks somewhat like ich or sometimes a fungus. This is a common aquarium denizen which feeds off the bacteria being shed by the fin rot. It is called epistylus and here is a link to more information on it:

10.2.4. Epistylus

The entire topic of bacterial infections in tropical aquarium fish is covered in more detail in this link:

10.3.11. Treating Bacteria

Return to Diseases Menu

Return to Bacterial Menu

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