ofcourse it is possible if you find that ectoparasite on fish gills. Trichodina infestation is not only related to urogenital system but also infest gills, fins and skin. This specie of trichodina is usually obligate in nature so it might possible that the diseased specimen was just looking for a space to enjoy weather and went towards gills where your student caught it and labeled as a criminal of gills which wanted to spread disease over there.

Good Luck!

Dear Dr. Sadar Aslam:

Thank you for your answer. Yes, it is probably possible to detect some trichodinid ectoparasites from different external site of fishes such as skin, fins and gills. As the urogenital system in fishes ends externally on fish external surface, so, it is possible to detect T. urinaria on fish gills. Please send me any published report on this case (T. urinaria on fish gills) if you have in hands. 

Best wishes and regards.

Furhan

Dear Furhan,

if you are sure with identification...

This species is highly specific and in Palearctic mainly connected with Perca fluviatilis only, and place of invasion - urogenital system! I do not know from Ukraine or Russia information about gills.

So, I hesitate. Maybe similar species.

Andrey

Dear Dr. Andrey A. Kovalchuk:

Thank you for your answer. Yes, the description and the measurements are in agreement with those of T. urinaria.

Best wishes and regards.

Furhan

Dear Furhan,

One more note: I'm not hesitating in yours qualification, but yours identification was based on vital specimens only, or you did silver impregnated, or staining by hemalaun preparations? And it was mass appearance of T. or alone cell find? I'm doing mainly with free-living ciliates but like lecture have to do with Biocoenology & Parasitology, so interesting case for me... And appear some typical damages on gills? Moreover appear on host species of fish other species of T. ?

Thanks forwardly,

Andrey

Dear Dr. Andrey A. Kovalchuk:

Thank you for your additional note. Concerning my qualification, my Ph. D. degree was awarded from the University of Wales, U.K in 1977 in fish parasitology (see my page on ResearchGate) and I am full Professor since 1989. As I mentioned earlier, specimens of T. urinaria were detected by one of my previous M. Sc. students but not by me. Photographs of this species were forwarded to me. If you are doing your work mainly on free- living ciliates, then you must be aware when contributing on parasitic ciliates.

Best wishes and regards.

Furhan

Dear Furhan,

thanks, perfect, so publish, as the same facts are known for other parasitic species, like parasitic (or better microphagous) cat-fishes from Southern America that attaking normally gills of fishes, but can attack urogenital organs. I passed hesitation when found marine species of the free-living ciliates in the Kiev reservoir - so interested in plasticity of ciliates both free-living & parasitic, and gathering interesting facts for possible book. I'm attaching for you one book from Russia (North-East) where gathered all finds of Trichodins in the area. As well, try to call Yuriy Kvach from Ukraine - he is in RG as well, as he worked (with colleagues) directly with Trichodins parasites (he will tell you more, as they worked with infestation of invasive species of fish by Trichodins and noted low specificity of  parasites against fish).

Good luck,

Andrey