Yum cha is not generally a lot of fish, mostly pork, squid and shrimp, chicken feet, durian, tofu, beef tendons bean paste - dammit, now I am hungry...
Never mind the restaurants - I would be more concerned about what is in most processed frozen food that you get from the supermarket. I don't recall ever filleting fish and ending up with a pile of exactly the same sized slightly off rectangle shaped bits:-?