Hah! I thought that you were asking about 42: the Answer to Life, the Universe, and Everything.
Okay, Morfowt, this is what you'd call a KASU. K.A. ___ Up.
Only blood vessels VERY close to the skin's surface (wrists, ankles, throat) would have even a little light inside them.
Still, sharks don't really NEED to see. They can literally FEEL the electric impulses of nearby life-forms.
Wait...then again...forget the idea that Marco'd be so electric as to confuse them. Marco himself would be too massive an electrical source to pose ANY problem; he'd be like a Van de graaff generator, too large and spread-out to make much an impact on the tiny sharks. High current is pointless with low voltage, and vice-versa.