can someone explain what monster fish were eating the creep? I didn't get it and I think Julia was confused as well.

I suppose they have such monster fish at Naples.

"I have one request of you people, and that is to have sharks with frikkin' laser beams attached to their heads!" ~ Dr. Evil

i guess these "monster fishes" are more likely to have been the wild hog struggling with death?^^"

Lucrezia talked to Mich about it. Seneca mentioned a certain fish species in Naples,but I didn't get the name of said species.

That was something Seneca wrote that Vedius Pollio, not an emperor but a friend of Augustus who was briefly governor of what is now Turkey did. The story goes that Pollio intended to execute a slave (who had dropped a drinking glass) by dropping him into a pool filled with lampreys, but his guest Augustus intervened, saving the slave, breaking the rest of Pollio's glasses, and having the eel-pit filled in. As with most stories of Roman excess, this one is anecdotal. The Roman tabloid press was a thriving industry contributed to by nearly all major writers (though the vindictive nature of powerful Romans meant that most of the bashing was done post-mortem). The story was used and elaborated on as a moral homily by various authors in the decades and centuries after Pollio's (and Augustus') death; no contemporary accounts exist.

Lampreys were a popular delicacy in ancient Rome, so it is not unlikely that a wealthy and extravagant Roman (such as Pollio was reputed to be) would keep a pool of them on his property. The rest is dubious to say the least. So they probably didn't exist, but that's okay, since it does serve the purpose of killing that awful king in our story.