I found the same on Channa spps. Probably this is ulcer(cancer). To verify, u may prepare squash onto slide and stain with HE..

As Bartolomeo said, it could be just an old wound. However, I will not totally agree it is not infected - you can see some kind of infection (fungi?, bacteria?) on the outside of operculum, tissues are also changed around the wound, but is it due to the fracture or infection? It's hard to say. Few things that might give some indication: what color are the gills? Was there increased excretion of mucus on the body of the fish or around the wound? Are there any other puncture wounds on the body of the fish?

It could be a remain from old mechanical wound, the infection (if it is infection) could be secondary thing.

This does not look ulcerous to me as there is usually additional inflamation in the region than this external image appears to have. If there is any additional pathology on the flip side of the operculyum, thaty may be useful to know. I agree as well with Bartolemeo, do not confuse ulcer with cancer. This is certainly not cancer.

It may be trauma - but looks more like sessile ciliate atachment site. Ciliates such as Epistylis frequently attach in a foresic association.You may be able to see ciliates if you make a scrape of the area surrounding the hole.

It looks like an old damage caused by a rock or an iron bar or a hook of a fishing rod and the wounded damage formed a scab.

Have you considered bow fishing? Not sure if that would be popular in your area.

It looks like a trauma. Infection might be secondary to that.

It looks like healed, perhaps accidental, old mechanical injury rather than any infection. If such holes are found consistently in other fish too, you may suspect or implicate to infection or pathological conditions. It may be ignored until one finds the pathogens or causative agents in the tissue samples around the hole

It could possibly be a fish hook wound, tag wound, or a parasite (lamprey?) mark. However, I would have to examine it more closely to make a more educated guess.

Is there any problem on the other fishes which are in the same pond.

Hi Pedram.

This is only a fish hook wound or mechanical injury that happened long time ago. As you have said, Fish could not be infected because In the attached photo, fish seems healthy specially in eyes and skin .

Yours

Hi Pedram,

I agree with colleagues that it looks like a fish hook or a old mechanical injury, there is not signs of inflammation or mucus around lesion. How many fish has been observed like this?

It is just a secondary bacterial infection. Primary may be injury.

It looks like a nearly healed failed hack of a heron. Look if there are other wounded fish in your pond.

It is likely a mechanical injury

This deformaty in your common carp is found in one case (Sporadic), I think that is a matter of genetical disorder.

I agree with the other colleagues. The first thing to consider is a mechanical damage, as you tell there are nor parasites or evident pathogens. Where did you fish it? Did you observe other animals with same microscopical sign?

Hi,

Thanks for all useful suggestions.

I think the following details might be helpful for our right decision;

Amongst 700 fish, which have been transferred to our lab, there is only one specimen with this problem (It was not epidemic). It was captured from a local warm-water farm in Iran, which fishing does not likely occur (i.e. hook injury as well as bow fishing cannot be possible). The parasitic fish like lamprey could not be found here too. The heron is more possible mechanical cause.

The color of gill and its mucus excretion are normal.

Ciliates like epistylis are more possible predisposing agent. There is a similar round hole in operculum of Tilapia, which has been reported with huge colonies of Epistylis transvaalensis, coinciding with bacterial and fungal infections. For more details, please see:

Basson L and Van AS J. Trichodinidae and Other Ciliophorans (Phylum Ciliophora), In Fish Diseases and Disorders, Volume 1: Protozoan and Metazoan Infections, Second Edition, Eds by P.T.K. Woo. Pages: 167- 170.

But the question is which test do you suggest rather than histopathology?

Thanks again!

Make a smear of the surrounding area- observe with microscope- staining is unnecessary

As more details have appeared from al these discussion, it appears that the image of the fish presented here (among total of 700 fish, (mortality of fish remains unclear yet?) appears to be clean and healthy and the possibility of infections of Epistylis or, any such ciliates are unlikely to cause such signs as exhibited.

I would suggest that the sign may be taken as exceptional, unusual, accidental, and the cause remains to be unknown.

The author seems to be unconvinced of the suggestions made so far by so many persons and he looks forward go for further experiments other than histopathology. Though it could be futile to take such an exceptional sample for further experiments, One can go for swap bacterial analysis / viral- cell cultures/fungal infections looking for evidence of microbial infections or ultrastructure evidences. All the best.

A idea this wound from foreign body penetrate from outside

Hi Bartolomeo,

Thanks for your invitation.

Yes, I am familiar with EAFP but I am afraid not able to use facebook site in Iran. If there is any link in other sites like LinkedIn, please introduce.

All the best

Please visit my personal site as follow:

https://sites.google.com/site/pmalekpouri/

https://sites.google.com/site/pmalekpouri/

This particular case seems more like a specific case and probably injury or mechanical damage rather than due to a disease. Nutritional or congenital deformations do not result in this type of hole... its more like shortened opercle, shortened or elongated jaw, bone deformation etc. Please give more details such as how many were seen like this? what lead to the observation? was there a behavioral abnormality..??

For me it also looks like mechanical injury, however the suggested smear of the area could be worthy to do too. Use of methylen blue could help to improve the microscopical observation. Also methylen blue on the injury can show you better the mucus covering on the area. Do you how old is this injury? Have you kept the animal in observation, if so is the fish healing as normal? or is the injury expanding? Is there any other observation that could lead to think about other cause further mechanical/biting (from a "partner" fish) injury that you could share with us?

All the best,

Patricia

Dear Pedram,

Thank you so much for your introduce my VNN group in your personal site.

I invite you to joint us in our Forum and would be more active in comments.

As you know, we have been involved in Viral Nervous Necrosis (VNN) disease since 10 years ago and succeed to isolate and identify of VNN virus as first time in Golden grey mullet (Liza auratus) in the Caspian Sea in 2004.

We designed an international team working including of Prof.T.Nakai,Prof.Chi Shau Chi and Prof. G.Bovo and my dear supervisor Prof.Hassan Hj.Mohd Daud from UPM as familiar scientists of VNN in the world.

Hopefully you will be one of our mainly active participants and let us to share your merit knowledge and experiences in our common interest field: VNN.

Meanwhile, regarding to your case, I suggest you that you will try to prepare suitable samples for histopathological study because you can observe probably damages in Light Microscope very well.

Good luck,

Kindly regards

Jalil Zorriehzahra D.V.M. & Ph.D

Head of Aquatic animal Health & Diseases Dept.

Head of Iranian Coldwater Fishes Scientific Society (CFS)

Iranian Fisheries Research Organization (IFRO