What does "rudd" mean?

Rudd: A fresh-water European fish of the Carp family (Leuciscus erythrophthalmus). It is about the size and shape of the roach, but it has the dorsal fin farther back, a stouter body, and red irises. Called also redeye, roud, finscale, and shallow. A blue variety is called azurine, or blue roach.