A Closer Look at Tail and Fin Rot – Part 1 (Symptoms & Causes)

Tail and fin rot is is an easily recognizable, and very common fish disease.  It occurs in aquariums, ponds, fish farms and the wild – both in rivers and in oceans.

It is a serious fish disease that can eat into the body of the fish after destroying all of a fin, leading to death.  Even before it gets to that stage, it can lead to severe complications.  Very often, a fungal infection takes hold in the affected fin, making treatment even more problematic.


The first signs of tail and fin rot are red streaks in the fins.  The edge of the fin will then lighten, before it starts to rot away and gain a ragged appearance.  Small bleeds may also be present.

Biological symptoms include variations in the levels of calcium and haemoglobin in the fish’s blood.

If a fungal infection occurs, the edge of the fin may be smoother i.e. get eaten away in a more uniform manner – and have a white edge.


Tail and fin rot is caused by bacteria.  The specific bacteria that cause the disease are common and found in most bodies of water, including ponds and aquariums.  The problem arises when the fish are subjected to an external event or environment that make them susceptible to infection.

By far the most common factors are poor water quality (especially raised levels of ammonia and nitrite), and direct trauma to the tail and/or fins.  Direct trauma can be a result of nipping by other fish, bad handling by humans, or sharp edges on plants and ornaments in the water.  The stress of any of these events leaves the fish open to infection.

There are three different bacteria that can cause tail and fin rot:

  1. Aeromonas – a rod shaped bacterium that can also infect humans, often resulting in the need for amputation.
  2. Pseudomonas – another rod shaped bacterium that has “superbug” strains found in hospitals that cause necrotizing inflammation in humans.
  3. Flexibacter – a bacteria that normally only affects fish, and is best known for strains that are bright yellow to the naked eye when colonies grow large enough.

To be precise, tail and fin rot is not a disease itself.  It is actually just a symptom of infection with one of these bacteria.

What the bacteria do is congregate in the intestine of the fish.  They then produce a mucous that contains molecules that are toxic to fish.  These toxic substances are absorbed through the wall of the intestine in much the same manner as essential nutrients, thereby entering the bloodstream.

The red streaks that are the first sign of tail and fin rot are caused by small blood vessels in the fins breaking apart under the action of the poison, and releasing blood.

Without a blood supply, the fins quickly lose their colour, break down and rot away.

While all this is happening on the outside of the fish, similar processes are destroying the blood vessels of the stomach, liver and kidney.

27 Responses to “A Closer Look at Tail and Fin Rot – Part 1 (Symptoms & Causes)”

  1. sheridanT Says:

    can anybody help?

    we have 9 goldfish in a 78 litre tank.. one of the fish has tail rot.. his fins were clamped for a few days and today his tail has rotted and is white..

    the tank is cleaned often and has plastic plants and one ornament, bubble snake and lights on about 8 hours a day. no hidey holes.

    water was changed yesterday and pH level today was in high sevens – am bring the pH down as we speak..

    are the other fish at risk of being infected? he is too far gone to save?

    thanks for any help

  2. ChrisLeonard Says:

    I have the same problem with a ryukin goldfish I bought a week ago.

    I’ve had two shubunkin, one is five, the other is 7 months and already 6 inches long.

    I have a Marineland tank with the BioWheel filter which they say never needs to be replaced, but it looked really grimy and I almost replaced it before putting the new fish in. Now I wonder if I should have.

    I just went to the pet store and got Maracyn and started treatment. I’m also moving the tank into the bathroom which is warmer; it’s been in the 20s and teens here lately and while my older fish doesn’t mind cooler water, this guy was in a really warm fish room and the change in temps may have been bad for his immune system.

    He’s got, or had, a beautiful fantail and it was fine as of two days ago when I was showing him to a friend, but this morning he was sitting on the bottom and when I fed him and he swam upward I saw he’s missing half his tail (he’s a very small fish, not even 2 inches.) He can still swim but doesn’t except when feeding.

    I just did a 1/3 water change yesterday, but the water already looks a little cloudy; again, I’m wondering about the BioWheel. Plus with Maracyn you have to remove the carbon from the filter, which means less goldfish poop getting filtered, and this ryukin is even poopier than my shubys were at the same size.

    Luckily he’s in a starter tank, I always put new fish in there to protect my other fish. When I first started with fish I lost two little goldfish to fin rot within a few days of getting them, but the first one was dead before I noticed the fin rot because their fins were transparent and it was too late to save the other who died the next day. This one has a mostly black tail so it was really noticeable that it was rotting off.

    I’m hoping to save him with the Maracyn, water change again tomorrow before I put in the second dose, raising the tank temperature. I even bought him a new kind of food, I asked the pet store what they had been feeding him and got that (I’d been giving him flakes, which my shubys love, but they’d been feeding pellets.)

    Some sites say to try Melafix first, but I figure if he’s lost half his tail in two days it calls for tough measures.

    You are doing all the right things but you may need antibiotics. My fish dealer recommended the Mardel line (Maracyn etc.)

    Hope our fishies make it!

  3. Fi Says:

    Hi, I’ve had a goldfish for 6 years and it belonged to another owner for a number of years beforehand so I am led to believe he is quite old. A few months ago I noticed that one of his fine was a lot smaller than the other (about the size of a pinky finger nail) whereas the the larger is about the size of half a pinky finger. But when cleaning him out the other day I noticed that bits of his tail had disappeared, looking as if they had been ripped off; tail and fin rot is the closest match I can find. He used to live with another goldfish who died a few years ago so he is now single who admittedly I do not clean out as often as I should but still fairly frequently. Is this tail and fin rot? I’m 14 so I have no idea how to check for the pH of water or what would help him.

    Please please help I love this fish so much and I hate to think that I might be losing him.

  4. jack Says:

    hi i also have a gold fish with fin rot .i am only twelve and me and my dad went to our local water gardens we got a medicen specified for fin rot .we also got some water condishener and mixed them with clean water and put that water in the fish tank.if this is any help to you

  5. liz Says:

    if you are suspecting fin rot, it’s maybe because of poor water quality. buy a freshwater test kit (or 3-in-1 test strips, cheaper) to measure ammonia, nitrite, nitrate and PH. ammonia and nitrite should be 0, you might get faint nitrate which is ok, PH can be 7.1-7.6 for goldfish. if ammonia and nitrite levels are higher, do a 30% partial water change every day for 4 days. then measure it again.

    is your tank properly cycled? please read up on nitrogen cycle in fish tanks. adding extra water conditioner helps with stress relieving, but don’t think it works for fin rot. your water conditioner should be used for removing chlorine from tap water, that you put in your fish tank. never, never put tap water in tank BEFORE adding water conditioner in it. for partial water changes, let the water age for a day or two before adding it to tank.

  6. Lauren Says:

    I got a goldfish from the fair
    i clean his water all the time and feed him properly. he has alot of room, and his water has a lot of surface for absorbing oxygen.
    he has black steaks in his tail and they were not there when i got him. I dont know if this is a disease or his ccoloring, but if it is, i want to make sure, so i can treat him.

  7. Emily Says:

    Hi, I got two fish in August. One of them died about two weeks late. What was weird was
    that this fish did not float he sank. I know he was dead cause he would’nt wake up.
    Is that normal? For a fish to sink like that?
    My second fish I could tell was quite disappointed, he would lay next to the dead one until we took him out.
    Now this same fish (the alive one who’s name is Fishy) for the past week has been acting strange.
    I thought at first he was lonely. Then he started not moving all day and just being active at night.
    He was okay at first staying up all night being asleep all day until he just stopped moving.
    He would move corner to corner but never swam around like he used to.
    I am really worried, he won’t even go to the surface to eat.
    He stays at the bottom all the time.
    I noticed last week that he was going a little white on his fins. I thought it was just his color.
    Today I woke up and noticed that he had this kind of white stuff, I have no clue how to discribe it,
    over parts of his fins, over the top of his eyes, and a bit on his sides. Its like some kind of white
    sorta gelly almost fluffy-ish looking stuff. My mom had this book that I quickly looked at. When I read about the diseases none of them really matched. The Fin rot was the closest thing in the book so I decided to look it up. It does not really look like the fin rot. Any ideas what it is or what I could do to help poor fishy?
    Hope you can help me,

  8. Jenifer Says:

    for your fish with the white fluffy ish looking stuff on his fins and eyes, get this stuff to treat it. its called Ick. Salt will help cure most of anything, but if the salt dont work, get the Ick. It is supposed to take the bad stuff off of his fins and put back the good bacteria. Hope this helps you.

  9. Caity Says:

    its really strange, I had four fish, Bill, Ben Red and Speckles, Id had Bill and Ben around 2 years and put the other 2 in and all of a sudden Ben died, then Bill 🙁 but red and Speckles are absolutely fine! noticed about 2 days ago red’s fins were shredding, but I got up the next day and they were back to normal!! can anyone explain how the hec he’s fixed himself so quickly????

  10. bob24 Says:

    One of my goldfish has black streaks on it’s fins too.

  11. Suzy Says:

    I am struggling. All my fish have died. The shop said it was fin rot. They also were covered inwhite spots then went all fluffy. Could they have had both rot and ich together? If so how can you treat both? It’s so hard to diagnose early. My latest fish are now getting sick. They are pretty lifeless, have some very tiny white spots on fins and body but also have red veins in their tales. Is it fin rot or white spot or both. Help

  12. alicia Says:

    my goldfish 2inch long, has developed the symptoms of fin rot too. his tail edges turned black last month. but then i treated it with melafin. it didnt grow more. then i added 2 silver dollars in the tank..
    the next morning i noticed that the silver dollars had eaten away my both goldfishz tails. i removed silver dollars from the tank.
    both of the goldfish still swim like a healthy fish. they dont seem sick. but the former fish developing tail rot has again got black streaks in his ragged tail..
    im still treating it with melafix and do water changes twices a week.
    the filter and oxygen system of the tank is perfect and the other goldfish is 100percent healthy. kindly help me out..
    should i continue melafix (its not working on the fish tail) or should i stop using it..
    im worried 🙁 i love my fishy!

  13. Jeff Says:

    We have had the same coy goldfish for about four years. One was very hardy and never seemed to get sick. The other would develop ick, and fungus about two to three times a year. About two months ago, my 12 year old son and I transitioned the fish from a 10 gal. tank to a 30 gal tank and they flourished; very happy in the larger surroundings.

    Two days ago I noticed our challenging fish’s rear fin falling apart in huge chunks; I have now learned this was tail-rot. The tank was filling up with translucent stringy looking strands, like thick pieces of thick fleshy thread… I mean a lot of it… hundreds of pieces. We decided to clean the tank right away. I scrubbed the tank in our bathrub, and to as I always do, I added a cap full of bleach while cleaning the glass and gravel to insure if there was any disease in the tank, it would be killed. I have performed this same cleaning method each time I clean the tank with no adverse results. I rinse it out thoroughly for about 10-15 minutes.

    We then added the water back into the tank; added Nitroban, Stress Coat, and Fungus Clear. After everything was set up and tested, I moved the fish from the old 10 gal. holding tank back into the 30 gal tank. The water was clear, everything seemed fine. They immediately started darting all over the tank, acting very unusual. Within 3-4 minutes, they were both upside down in the bottom of the tank. I grabbed them out with my bare hands and tried to revive them in the holding tank. They responded half-heartedly, but after working with them for about 5 minutes and seeing they were basically in a comatose state, I did not want them to suffer any longer; heartbroken I pulled them from the tank.

    I felt terrible. They were a part of the family. What the heck did I do wrong? When I tested the water, it seemed fine. Several hours later when I reviewed the testing strip, the Acidic pad was hard, crusty and eaten away. The water must have been deadly, but I didn’t do anything different this time than we have done every two weeks for the last 4 years.

    We had these fish from the time they were less than an inch long until now when they measured roughly 7 inches in length. I can’t believe this happened so quickly. If anyone can help me understand what I did wrong, I would be grateful.

    Thank you, Jeff

  14. Rachel Says:

    We bought 5 goldfish 6 years ago and they all survived until this year, cant figure out whats changed. we now only have 1 left who has now developed a frayed fin and tail, seems to sleep on the bottom alot. Is this fin rot? we have added other goldfish to the tank in the last yr to replace the lost ones for our childrens sake but they always die within the 1st week. Whats going on?

  15. ginger Says:

    can a tail grow back if it rot all the way off been treating it. she swims and eats good but no tail looks funny but seam ok

  16. sam Says:

    I have six goldfish two of them have fin rot and bood stains all over them. They all have white spot to. The two with fin rot are lazing around and every so often they come out for a swim and food then go sleepy again. Ive cleaned them out and treated water but they keep getting this. What can i do. Am i doing something wrong?

  17. Vicki Says:

    I brought a fish tank (little with a small pump) last week cleaned it all out (just water) put the water treatment in it & left it for about 4 days before I brought my fish!Got my fish (Clouse he’s a fancy Goldfish) on Tuesday & did what the fish centre said about putting him in the tank! I’ve noticed tonight that he had some funny largish White spots on his tail, they don’t really look like White spot because they’re too big from the pictures I’ve seen!There is a spot on the very edge of his tail that has a bit that looks like it’s chipped off! Is this fin rot??

    Don’t want Clouse to die!

    Help pls if anyone has any ideas I’d be really grateful for anything!


  18. kat Says:

    I brought 5 goldfish bout 12 weeks ago for my children, i brought a new tank with fillter n pump for them and followed what the shop told me to do with water and adding them ect ect, i change the water often and i treat the water with white cyctals (for hard water ect) anyway i noticed a few days ago that 1 of the fish (bear) had totaly lost its fin & ive just noticed that his tail is rottening away from the outside, hes swimming about normally and eating well, im 99% certain after reading this site that it is fin rot and a bad case of it but not sure what to do now ive tryed getting hold of 3 different pet shops but no one answering the fone,
    the other 4 goldfish seem fine, fin in tact and no signs of fin rot what are they chances that they are gonna catch it to? should i remove bear from the tank and put him/her in a tank on its own
    would be grateful for any advice about saveing the 4 good ones as i think its to late for bear 🙁

  19. Abigail Says:

    This is all very sad. I’m very sorry to all who have lost fish; I myself have lost a couple. However, I’ve found out some essentials to keeping the fish alive, thriving, and happy. Understand that I am no expert(I’m 15), but have simply discovered helpful tidbits through experience and research. Also, you must understand that fish from stores are all likely to have diseases that they bring back to your home with them. It is not a good idea to immediately place new fish with the ones you already have. Here are ways to PREVENT disease.

    Important For Healthy Fish:

    *clean water
    -treated if it is tap water(water conditioner can be bought at a store)
    -bottled water works too
    -you must change the water about every week so acid doesn’t build up and hurt the fish(google nitrite/nitrate)
    -a filter is almost necessary for keeping healthy fish because of the amount of waste they produce(which becomes toxic acids)

    -you DO NOT want to feed a fish too much
    >a little bit a few times a day works well
    -try to feed the fish more than just flakes
    >vegetables like peas, lettuce, spinach and cucumber can be cut up or hung from the tank to nibble at and eat
    >some fruit is good too, but feed sparingly(like a few times a month)
    >you can buy live food like brine shrimp, or go outside and get some mosquito larvae or earthworms
    >pet stores sell a lot of these foods, so check it out
    -flake food is dangerous because it has air in it and this air can get stuck in the fish’s swim bladder and cause them to float on their sides or upside down. it’s good to soak the flakes before feeding so they don’t have air

    *A good tank
    -big enough for the number of fish it holds(at least 2 gallons per fish and that’s really pushing it)
    -NOT a goldfish bowl; the small hole doesn’t let enough oxygen into the bowl
    -things to hide behind so the fish feels safe(plastic plants, clean rocks, etc…)

    This is all I can think of for now. Please feel free to add to it and I hope it helps!

  20. Melissa Says:

    I have pond goldfish who have been healthy for 3 years. Lately the older, larger ones started developing ragged looking tails. Now I notice the scales on the backs near the top fin are starting to look bubbled up, almost like air is underneath the scales. Also looks this way on the fins. What is this? Can I treat them? The only change is we have store bought finches that bathe in the water fall. Could it be from the finches? Please reply as I love these fish so, I hate to see them suffer and die.
    Melissa Evans

  21. BARBARA Says:

    Iuse five eye drops of each of these meds PIMAFIX/MELAFIX all pet shops carry this it saved my fish and he had 85% tail lose his hole tail was restored put fish in its own tank five gal leave in meds 20 to 30 min.than put back in your main tank. will treat open redfungus/open wounds sores/fan and tail rot/eye cloud/pop eye/body slime/.DO THIS FOR SEVEN DAYS. GOOD LUCK FISH OWNERS

  22. iluvmyfish♥ Says:

    ok so i hav this gr8 fish, his name is fredrick, he has these rips in his back fin and little white bubbly things. i also have another goldfish who is fine. i dont have a filter my ph is is about. 7.0 and i dont want fredrick to die…what do i do??? it might be cuz i dont have do filter but i change da water and clean out the bowl every other day. sigh

  23. Thomas Says:

    I had two fish. one of them died of dropsy last year. So about 2 weeks ago I bought a new one. I went on vacation leaving them both at home giving them a weekend feeder. I came home and saw that they were both doing well. the next day, I saw that the larger one was sleeping under one of the ornaments and couldn’t get out. so I lifted up the ornament and as he swam out, I noticed that all his fins were clamped, and his back fins were torn with red streaks on them. I am only 10, and my mom won’t buy any medicine too expensive. can u plz help? My family and I had this fish 4 about 2-3 years and we care about it. Can you help me or prescribe something? Plz contact me ASAP!

  24. Mariah Says:

    Ok …… I had tropical fish but they did not work so I bought 2 goldfish and they are awesome except fredly (goldfish) tail is spitting and has black stuff along the edges. Also I have a ghostcatfish and a frog and 2 bleeding heart tetras and 1 guppy. HELP PLEASE!

  25. Kay Says:

    Hi All
    I have recently changed from a 48 ltr to a 54 litre.
    I like my fancies and have also f=got a few leapord danios and minnow.
    At late they all seem to be dying off one by one. I have water testing strips and as soon as something looks off I do a 50% water change using my aqua safe.
    Now my oldes fancy has fin rot. Not looking good 🙁 I have treated him but his tail is still receeding and he spends all his time at the bottom f the tank. Gill movement seems slow/laboured also.
    All other fish are fine but are treating them together, why am i loosing my fish? I would like to go tropical but if i cant keep goldfish, i have no hope!!!

    please help this is really getting me down 🙁

  26. Katie James Says:

    My goldfish has fraying fins for the last two days and today there were blood streaks through her tail, she barely uses her gills and swims frantically around the top of her tank. A month and a half ago the other 4 fish that shared her tank were killed by some unknown bacterial disease. I’m 11, and even though the disease sounds pretty close to Finrot my parents don’t think it’s a good idea to buy really expensive medicine because they might not work. How much does Melafix cost?

  27. Helen Says:

    I have had my fish for little over two years. Bella is a cosmic goldfish, Tangerine is a regular golden goldfish and Spooky is a telescope black goldfish. Bella has had minor fin rot in the past. I have used Melafix to help in the past but not sure if it has ever really fixed her fin rot problems. Just recently I have gotten very sick from food poisoning and I have noticed a change in Bella’s behavior. She has been hanging out more on the bottom of the tank, hasn’t been swimming around like usual, energy levels are lower and she just seems and feels off to me. I can feel it crazy or not I know and love my animals. I have noticed a collected small “pile” of fish poop, which has never happened in my tank before. Her poop has a thin shell thats somewhat clear but also a coating of discoloration. I’m wondering if she is either backed up and not feeling well but then I noticed some of her fin very small pieces that have fallen off and are floating in her tank. I’m very worried and not sure what to do.

    I tested the water in their tank everything looks fine except Total Alkalinity, which I’ve had problems since I’ve been in this apartment but any suggestions to get this one perfect would be great. Also their pH levels weren’t good which I don’t get because I cleaned their tank 9 days ago. Tomorrow I am planning on cleaning their tank doing a 30% water change for the next 4 days and ONLY using purified water so it’ll have better water for them and cycled out the bad water. Don’t you think this will help get rid of their current water and have it mostly replaced with the purified water? What can I do for Bella? I do not want her to pass away!
    Please Help!!!

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