Mysterious patches on my tetras

[Tina1704]

Hi everyone, I have a 350ltr tank containing various fish, I have, I think they are Columbian tetras that have all developed black patches, I have asked in my local pet shops and nobody can tell me how to treat it or what it is. It hasn't affected any other fish except the 6 of this type, any help how to treat would be appreciated. It started on just one a couple of weeks ago and now all 6 have it. Bought them in January so they are not new to the tank, water quality is all good and I haven't added anything else since. TIA

 

[Slaphppy7]

Welcome to TFF

Those are indeed Colombian tetras...years ago, mine had the exact same thing as yours, and they slowly died off over time...I was never given a definitive answer on what it was, though

@Colin_T , have a look, please

 

[Tina1704]

Thank you, I'm wondering if it is a disease associated with that type of fish. I've had it in a tank before about 6 years ago, probably the same type of fish as I like the larger tetras. Strange how it doesn't spread to the other fish. I am hoping to come up with an answer to treat them before lose them.

 

[Slaphppy7]

Thank you, I'm wondering if it is a disease associated with that type of fish. I've had it in a tank before about 6 years ago, probably the same type of fish as I like the larger tetras. Strange how it doesn't spread to the other fish. I am hoping to come up with an answer to treat them before lose them.

I hope you get some good responses, as I am curious about diagnosis & treatment as well

 

[Colin_T]

need pictures that are in focus

the only fish disease I know of that has black is a parasitic worm that makes small black dots on the body. the fish in the picture do not have that.

black patches on fish are usually bruises or chemical burns.

did you do a water change or anything to the tank a day or two before this first appeared?

do you dechlorinate new water before adding it to the aquarium?

 

[Tina1704]

need pictures that are in focus

the only fish disease I know of that has black is a parasitic worm that makes small black dots on the body. the fish in the picture do not have that.

black patches on fish are usually bruises or chemical burns.

did you do a water change or anything to the tank a day or two before this first appeared?

do you dechlorinate new water before adding it to the aquarium?

Did a water change after I noticed it thinking it could be ammonia levels, but have also done a water test which shows everything is good. I use pure water system when I do a water change, always have and no problems before, it is only the Colombian tetras that have any patches, all other fish are fine.

 

[FranciscoB]

I too keep Colombian tetras and have never seen that (on those fish or on any others). It seems odd that the black blotches seen to occur on both the body and fins (second photo). Very curious about it. The only remotely similar thing I have seen is something that seems to affect lemon tetras only - the entire caudal peduncle becomes darkened in individual fish, usually the largest. No other blotches, no change in behavior or appearance, but over time (months), affected fish die, and eventually appears on another fish, never all of them at the same time within a school. I have no explanation for it, I have considered it part of senescence (in my own ignorant mind).
Slaphppy7- How long would you say it took from observing the black patches on a fish, and the death of that individual?

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[Slaphppy7]

I too keep Colombian tetras and have never seen that (on those fish or on any others). It seems odd that the black blotches seen to occur on both the body and fins (second photo). Very curious about it. The only remotely similar thing I have seen is something that seems to affect lemon tetras only - the entire caudal peduncle becomes darkened in individual fish, usually the largest. No other blotches, no change in behavior or appearance, but over time (months), affected fish die, and eventually appears on another fish, never all of them at the same time within a school. I have no explanation for it, I have considered it part of senescence (in my own ignorant mind).
Slaphppy7- How long would you say it took from observing the black patches on a fish, and the death of that individual?

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Probably 2 or 3 months from the onset of the dark patches...the patches were small at first, then grew larger over time

Like the OP, it affected my Colombian tetras only; no other fish (mainly other tetras, I'm a fan of all Characins) were affected

I was on another forum at the time, with some members who were very knowledgeable with fish diseases, and none of them could figure it out

 

[Tina1704]

I too keep Colombian tetras and have never seen that (on those fish or on any others). It seems odd that the black blotches seen to occur on both the body and fins (second photo). Very curious about it. The only remotely similar thing I have seen is something that seems to affect lemon tetras only - the entire caudal peduncle becomes darkened in individual fish, usually the largest. No other blotches, no change in behavior or appearance, but over time (months), affected fish die, and eventually appears on another fish, never all of them at the same time within a school. I have no explanation for it, I have considered it part of senescence (in my own ignorant mind).
Slaphppy7- How long would you say it took from observing the black patches on a fish, and the death of that individual?

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The first one appeared to have the patches about 3 weeks ago, he doesn't look so good now, don't think it will last the day. The others are still ok, just black patches, I was hoping to save them but don't know how to treat them.

 

[Colin_T]

You could take the sickest one to a fish vet and have them necropsy (animal autopsy) it for you. They should then be able to tell you exactly what it is. But it will cost a bit of money.

Most states have a Department of Agriculture and these usually have a fish health section. They normally do fish necropsy and don't charge if it's for a home aquarium, but you would have to check because policies vary between states.

I wouldn't treat for anything until you know what the actual cause is.