The only thing I ever fed worms to from the garden was my axolotl. He'd snap up the end of it and swallow it all down.
I found two different kinds of earthworms in our garden... one, was lighter in colour, pinkish - you know, your kind of "standard" earthworm... The other was a darker almost reddish-brown colour with faint pale stripes.
There's one way to differentiate between them... the reddish-brown one STINKS, especially if you cut it open. My axolotl couldn't digest those. Something wierd about them, but they came out of the ground like the others did, so I don't know.
I've never fed worms to tropical fish though... just freeze-dried tubifex ones, or blood worms.