my cousin has kept an eel few months back, i think adult size, quite long....in a 5 ft tank( specially for it).
i think he fed it dead prawns( if i remember, its cooked prawns, cause its orange)...and eels are kinda 'blind'....have to brinng the prawn right in frront of it to sense it, even by smell
mix with fish? according to him, he said can be mixed, cause maybe that particular species takes prawns only....
juz my 2cents