Fluorescent animals have been in the science pages of late, and a piece in the Courant drops this little tidbit:

The first recorded use of fluorescent protein goes back to the first century, when Pliny the Elder rubbed a jellyfish on the bottom of his walking stick to illuminate a path.

And for once the reference doesn't seem to be apocryphal ... from the NH 32.141 (via Lacus Curtius):

Pulmone marino si confricetur lignum, ardere videtur adeo, ut baculum ita praeluceat. —