Ribeye the Fish -- Glub, Glub, Dead.

Ribeye the Fish -- once known as "The Snarkiest Fish in the Z" -- has died ... TMZ has learned.

Sources close to the situation tell us ... one of the TMZ staffers found Ribeye floating in his tank ... unresponsive to various taps on the glass.

The fish -- only a few months old -- was given a burial at sea ... via the toilet in the men's bathroom.

Harvey Levin released a statement saying, "He was a good fish ... he will be missed."

Harvey's asst. Tyler adds, "Not much of a swimmer though." R.I.P.