What is "gobio fluviatilis"

Gudgeon \Gud"geon\ (g[u^]j"[u^]n), n. [OE. gojon, F. goujon, from L. gobio, or gobius, Gr. kwbio`s Cf. 1st Goby. ]

1. (Zo["o]l.) A small European freshwater fish ( Gobio fluviatilis), allied to the carp. It is easily caught and often used for food and for bait. In America the killifishes or minnows are often called gudgeons.

2. What may be got without skill or merit.

   Fish not, with this melancholy bait, For this fool gudgeon, this opinion.
   --Shak.

3. A person easily duped or cheated.
   --Swift.

4. (Mach.) The pin of iron fastened in the end of a wooden shaft or axle, on which it turns; formerly, any journal, or pivot, or bearing, as the pintle and eye of a hinge, but esp. the end journal of a horizontal.

   6. (Naut.) A metal eye or socket attached to the sternpost to receive the pintle of the rudder.

   Ball gudgeon. See under Ball.