one of my Oscars (about 13", it was a long finned one) got me on my finger once.... looked like a bunch of scratches, bled a bit, and got kindof swollen.
I did an internship at an aquarium, and when we'd feed the cow nosed rays, they'd suck on the palm of your hand... it was like a mini vacuum cleaner, they were pretty strong.
The goldfish/koi in my pond will nibble on fingers if you barely put them in, that just tickles, and kids that visit love it.
not bites... but still drew blood....
I used to have a striped raphael... I was moving him, and he got tangled up in the net. As I was getting him loose, and I guess had my fingers on either side of his body, it tightened up, make this creaking noise like an old door, and pinched my fingers between his fins and his side.... nice little spikey needle punctures from that. O, and got stabbed in the palm with some catfish fin spike once.