Unusual Intestinal Parasite/Egg Casing Identification?

Jules96 · Jan 30, 2026

Hi all! We have a wild caught blenny in one of our aquariums. He has been with us for about 4 months now, his belly has gotten larger, but it's a super hungry fish so, I didn't think much of it. This past Monday though, he had something hanging out of him. I figured it was a parasite and pulled him into quarantine for treatment. Yesterday it fell off and I could get a closer look, but I can't find much online and it doesn't look like any of the parasites I'm familiar with. Anyone have ideas of what I'm looking at? Aside from the big belly, he was breathing really heavy as well but that has improved since treatment in quarantine. Below is a (not great) photo of it attached to the blenny, and then some closer views including under a microscope.

vetteguy53081 · Jan 30, 2026

Jules96 said:
Hi all! We have a wild caught blenny in one of our aquariums. He has been with us for about 4 months now, his belly has gotten larger, but it's a super hungry fish so, I didn't think much of it. This past Monday though, he had something hanging out of him. I figured it was a parasite and pulled him into quarantine for treatment. Yesterday it fell off and I could get a closer look, but I can't find much online and it doesn't look like any of the parasites I'm familiar with. Anyone have ideas of what I'm looking at? Aside from the big belly, he was breathing really heavy as well but that has improved since treatment in quarantine. Below is a (not great) photo of it attached to the blenny, and then some closer views including under a microscope.

This may be coccidia which other than elevated iodine has no specific cure
@Jay Hemdal - your thoughts?

Jay Hemdal · Jan 30, 2026

Jules96 said:
Hi all! We have a wild caught blenny in one of our aquariums. He has been with us for about 4 months now, his belly has gotten larger, but it's a super hungry fish so, I didn't think much of it. This past Monday though, he had something hanging out of him. I figured it was a parasite and pulled him into quarantine for treatment. Yesterday it fell off and I could get a closer look, but I can't find much online and it doesn't look like any of the parasites I'm familiar with. Anyone have ideas of what I'm looking at? Aside from the big belly, he was breathing really heavy as well but that has improved since treatment in quarantine. Below is a (not great) photo of it attached to the blenny, and then some closer views including under a microscope.

Welcome to Reef2Reef!

Those sure look like eggs. My guess is the fish was egg bound. Coccidea would be round like this, but much smaller.

Jules96 · Jan 30, 2026

Jay Hemdal said:
Welcome to Reef2Reef!

Those sure look like eggs. My guess is the fish was egg bound. Coccidea would be round like this, but much smaller.

I sure thought those looked like eggs! Is there any harm or benefit to continuing the api general cure tx in quarantine?

Jay Hemdal · Jan 30, 2026

Jules96 said:
I sure thought those looked like eggs! Is there any harm or benefit to continuing the api general cure tx in quarantine?

No direct harm in that, but just be aware that when fish release a bound egg mass like that, it usually includes reproductive tissue and that in turn can cause health issues, including possible death.....

MnFish1 · Jan 30, 2026

I would consider stopping general cure - just to minimize potential issues - and there is no diagnosis to support it.

xzt · Jan 31, 2026

That is the egg laid by a fish.

Jules96 · Feb 4, 2026

Jay Hemdal said:
No direct harm in that, but just be aware that when fish release a bound egg mass like that, it usually includes reproductive tissue and that in turn can cause health issues, including possible death.....

Just an update for anyone interested/who sees this in the future, the blenny did die. I stopped the general cure after the first dose and just kept her in quarantine. She never passed any more eggs and her belly stayed pretty big, respirations got faster and she stopped eating these last two days.