Hi everyone. I'm a sort-of longtime lurker, first-time poster :) Nice to be here!
I've bought frozen tilapia in 2lb bags from Costco a few times now. Can't remember if it's the loins or fillets (I think it's the loins- I don't know fish anatomy well :P) Reason being that it's quick to thaw and quick to cook, so it makes a fairly easy dinner. However last time I bought tilapia, one of the pieces had these very thin, black thread-like things in its flesh. I cooked the fish fully and figured they're probably harmless, but they still kind of squicked me out, especially as I had not seen them in other pieces before. They only showed up after I flaked the fish a bit- they weren't on the surface. Also, the tilapia already comes de-boned (another convenience.)
What are these thready black things? Are they harmless, as I suspect?
Bonus question: are there any seriously harmful long-term effects of eating lots of tilapia? By lots I mean maybe 3-4 loins a week, and the loins aren't huge or anything. Of course I'm going to work some different kinds of fish in there too, like salmon, but since the tilapia is relatively cheap I'd be eating a lot of it. I live in Las Vegas, if that helps.
Thanks in advance for any help!