# lesion on Cardinal Tetra



## n0otro (Nov 22, 2006)

My current planted tank has been established for ~20 months.

I haven't had any problems with fish diseases or parasites until a strange lesion showed up on one of my Cardinal tetras this week.

I'm thinking it's a bacterial infection akin to _Aeromonas salmonicida_.

Has anybody seen this before? The fish doesn't appear to be deterred.


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## Zapins (Jul 28, 2004)

Looks pretty bad. I'm not sure what it is, though I recently found out that parasitic worms can cause lesions like that. What is that white area in the middle? Is it raised?

Great quality picture, using a dissecting microscope?


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## n0otro (Nov 22, 2006)

Zapins said:


> Looks pretty bad. I'm not sure what it is, though I recently found out that parasitic worms can cause lesions like that. What is that white area in the middle? Is it raised?
> 
> Great quality picture, using a dissecting microscope?


Photo was taken on a Leica modular dissecting scope with a sony SLT-A55V camera and LED lighting.

The middle area appears to be flesh, i'm assuming from inside. Yesterday it looked like it was hanging out further, today it didn't look as bad.

I took a scraping and threw it under a 63x oil immersion objective and definitely didn't see any worms.I saw plenty of bacteria, but I can't be sure if they were anything more than the typical surface microbiota, or opportunistic bacteria feeding on a lesion caused by something else.


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## Zapins (Jul 28, 2004)

My guess is that whatever originally caused it the fish will most likely die from bacterial infection if not cured. That lesion is an open wound straight to the environment which is full of bacteria. I wonder why the flesh is clear around the wound, it almost looks necrotic the sort of thing a fungus would do. Its hard to tell but is the wound a clear hole straight through to the organs underneath or is it subcutaneous only? The fish would have better chances if it was above the muscle layer.

It seems like you have access to lab equipment, so it might be possible for you to see if it is gram - or + bacteria and then attempt to cure it based on which type of bacteria it is.

Crystal violet or Gentian violet (also known as Methyl Violet 10B, hexamethyl pararosaniline chloride, or pyoctanin(e)) can be used to tell what it is. Gram - will not stain with this dye. 

I've got to say though, you would be surprised what fish can survive through. I once went spear fishing and shot a fish that escaped after the spear went through it and I ended up finding the same fish three days later in the same area, slightly paler but alert, swimming well and much more wary of me.


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## n0otro (Nov 22, 2006)

Zapins said:


> My guess is that whatever originally caused it the fish will most likely die from bacterial infection if not cured. That lesion is an open wound straight to the environment which is full of bacteria. I wonder why the flesh is clear around the wound, it almost looks necrotic the sort of thing a fungus would do. Its hard to tell but is the wound a clear hole straight through to the organs underneath or is it subcutaneous only? The fish would have better chances if it was above the muscle layer.
> 
> It seems like you have access to lab equipment, so it might be possible for you to see if it is gram - or + bacteria and then attempt to cure it based on which type of bacteria it is.
> 
> ...


One of the grad students in the lab is teaching staining techniques in in micro right now and offered to have his students work up some tissue from the fish, but I don't know if it will do any good because there appear to be a number of different types of bacteria, probably both gram +/- so the results would likely be ambiguous. The lesion appears to be a direct opening to the fish's ventral cavity so I don't have much hope of him surviving in the long term. I don't have a spare quarantine tank in the lab so he won't be getting treated either. I'll just be keeping an eye on him, and if it looks like he starts going down hill, i'll probably euthanize him and do a more rigorous inspection with a scalpal... As of right now he's still eating like a pig.

I use to do alot of spear fishing and can certainly attest to _nearly_ catching a fish, feeling bad that I mortally wounded him, but he still got away, and then seeing him on subsequent dives... although i'm sure in the long run they mostly just become moray fodder as the bacterial infections begin to set in...


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## n0otro (Nov 22, 2006)

Just an update:

More than a week has passed since I took the initial round of photos, and after looking at the ailing fish under the dissecting scope today, i'm relieved to say that he appears to have been feisty enough to fend off whatever sort of bacterial infection he had. I had to stare at the school of nine fish for a solid 5 minutes before I could even identify which one it was that had the lesion. I still don't know what it was, or whether or not it was even bacterial in nature. It may have been an encysted parasite escaping it's host phase... in which case i'll be keeping a close eye on the rest of the school!


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## Zapins (Jul 28, 2004)

Wow! Amazing that it could heal from such a bad looking wound. I'm glad to see it is better. I guess that grad student won't be too happy now


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