(1) A large, plump fish, not necessarily sporting impressive length but necessarily displaying mass girth.
(2) Anything of impressive girth or that is simply impressive.
(1) The guide pulled the rainbow engorged with salmon eggs from the stream and shouted, "a toad fish."
(2) Eyeing the cupcakes, little Nicky grabbed for the biggest of the lot, screaming "toad fish."
A large turd of such size and girth that a small portion at least pokes itself out above the level of the toilet water-line. In this sense, the crap is like an ice-berg in that roughly 2/3 of it floats below the water-line.
Man, I was hurtin' after stuffing my face at Thanksgiving but all is well now that I've floated a chocolate berg.