Most small fish will eat them. Bettas I know for sure will.
I've seen my green barb pull a nematode (at least that's what I think it was, long light colored worm looking thing) about an inch long off of a branch and polish it off. My white clouds pick at the few planaria on the glass when I turn the lights on at night.
Why do you ask? If you are having a problem with planaria and nemotodes you have other issues in the tank (like extreme overfeeding) that a micro-fauna eating fish isn't going to help you with.
i have some planaria but its not overflowed with it... it may be sad what im doing but it works, along with my arowana i put a couple a feeder fishes along with it and the feeder fishes eats the planaria ie( guppies, rossy, goldfishes). i was wondering if there would be a fish that would be compatible with the arowana that feeds on the planaria
yes they are, i just had my own little run in with em. my two white clouds (male and female) were eatin em like crazy when they payed attention to em, but i got concerned because of their numbers. there were atleast 100-200 in the tanks so i transferred the white clouds into my guppy tank and put freezing cold water with ice cubes in the nemetode tank and they all seemed to have died. i guess it worked out well tho cuz i'm tryin to breed white clouds and maybe it could help my female in the longrun but i felt they had to go. they came off my anacharis from my pond.