I've tried feeding the following list of aquatic plants, and probably others I can't think of. Some he'll tear at making a mess, but not eating.
Anacharis
Amazon Sword
Water Lily
Duckweed
Japanese Peneywort
Water Hyacinth
Hornwort
so far the one he does eat is Frogbit. I could grow just Frogbit in the tank, but that is such a ware of the tank's real-estate and growing equipment.
oh and snails - ramshorn snails - Thor definitely likes them, so that's it two items.
I really want to grow another plant!
please somebody, what aquatic plants (besides those listed above) will your RES eat?