Possible gill fluke or parasite on guppy gill?

[targetfish]

Content warning: Necropsy image
Deceased guppy gill close up for diagnostic purposes, do not scroll further if that may upset you.

Hi everyone,

I did a necropsy on the Poecilia reticulata (guppy) that died in my tank because there was flashing behavior in the fish in that community tank. I was waiting to see if there were other signs of parasites since there was no visible velvet, ich, or red on the gills and no laboured breathing or gasping. Tank is fully cycled and parameters are within normal range.

I found an oval structure firmly attached to the gill. It looks slightly translucent and cream-white. I'm wondering if this is possibly a gill fluke or remnant of one, stray tissue, encysted parasite, or something else?

Can anyone tell me what it is and how to treat it? (if treatment is applicable)

 

[targetfish]

In need of an answer, I'm worried about my other fish

 

[Fishfur]

About how many mm long is that thing & approximately how wide across the widest part?

What is it like to the touch?

I mean is it hard like a rock, firm like an old cheddar cheese, soft but springy like fresh bocconcini or very soft & squishy?

Sorry for those comparisons to cheeses, but they were what came to mind.

If you have a magnifying glass, slicing that thing lengthwise might show something useful - you can shoot pics through a clean magnifying lens to get something akin to a macro shot.

 

[targetfish]

About how many mm long is that thing & approximately how wide across the widest part?

What is it like to the touch?

I mean is it hard like a rock, firm like an old cheddar cheese, soft but springy like fresh bocconcini or very soft & squishy?

Sorry for those comparisons to cheeses, but they were what came to mind.

If you have a magnifying glass, slicing that thing lengthwise might show something useful - you can shoot pics through a clean magnifying lens to get something akin to a macro shot.

Ah, unfortunately I have disposed of everything now, but I can say what I recall.

It was probably ~1.5mm long, 1mm wide? Too small to touch with my fingers but it didn't change shape or get damaged easily like the other tissue, but wasn't hard-hard like a rock, so I'd go with the firm like an old cheddar cheese comparison.

The picture was taken through a 10x jeweler's lens.

I really appreciate the response! I was worried I wasn't going to get any help

 

[Fishfur]

This is strictly a guess but it may have been a fish louse - Argulus spp. , and most probably a young one not yet of breeding age, given the size.

They more often attach to skin but they aren’t picky. Unless you find more of them on other fish I don’t think I’d worry at this point.

Treatment is possible if need be, but not easy, The best treatment used to be trichlorfon, an organophosphate pesticide. But it’s either banned or impossible to obtain in a great many countries.

Diflubenzuron works so far as I know - it’s a pesticide as well, which is a chitin synthesis inhibitor. Intereferes with moulting so the pests never make it to adulthood.

Brand name is Dimilin. I have no idea how easy or difficult it is to obtain.

Hard to say where it would have come from as they are obligate parasites, but unlike most parasites they can move from one host to another as they choose. So maybe it was a hitchhiker.