Hey,
I've kept little Eels (<15cm) from the Hawkesbury with Rainbowfish(5-15cm) before, and they were fine.
As to what they eat: Anything that goes in the gob.
I don't know if mine were particularly messy or not.... cant remember now.
And don't pay a lot for one.
You can go to your nearest permanent body of water with a fishing rod and a packet of prawns at night, and watch the Eels roll in. Hook size and bait size will dictate Eel size, to an extent.
You'd hafta quarantine it very thoroughly if you caught one though.
I have kept a lot of fish i've caught while fishing, and they're usually fine, so don't worry about it's mouth. Eels are tough as nails anyway.
As far as i know there's only 2 freshwater species in Australia, being Short-finned Eel, and Long-finned Eel. (i could be wrong though, i'm no Eel expert)
A "QLD Mottled Eel" is probably just a marketing ploy
I don't see what the problem would be, as long as there's hidey holes for both, and they're roughly equal in size. I'd say a 25cm Oscar and a 60cm Eel should have no problems together, especially in a 6ft tank, so just work on that scale.
You never know unless you try it.
HTH.
Cheers,
Andy
