Anisakis Simplex I think it is.... The Parasite.
I seem to find them in about half of halibut I encountered in "my research" so far... if not more.
Nasty chit. It's easy to over look 'em, even if you're looking hard. I was finding them wiggling on the top of fillet, that stayed overnight in the fridge in ziplock bag... on the fish that was "clean", I thought I didn't see any when I cut it.
They mostly seem to be hanging on the guts, but often they seem to take a seed on the lower belly, on the inside. Whole bunch of them bundled up, rooted in the belly flash. Sometimes on the upper stomach fillet....
That piece of the belly... hazardous material.
Throw away, or maybe take it to treat the boss you absolutely hate.
Supposedly, humans are too tough for Anisakis Simplex; they die if they end up, in majority of humans... but still - in some rare cases, they are fine with some unfortunate folks as hosts. Often there's is an allergic reacton... Scary.
"Cooking fish to 140ºF (60ºC) for 10 minutes, freezing fish at -4ºF (-20ºC) for at least 7 days, or blast freezing fish to -31ºF (-35ºC) for 15 hours kill the larvae."
http://en.wikipedia.org/wiki/Anisakis
http://blogs.discovermagazine.com/lo...in-your-sushi/