no to turtles.
you dont want an expensive fish like that becoming turtle show would ya...
as for other fish,more gulpers and fish that are high bodied and should be much bigger than the gulper.
NO AGGRESSIVE FISH.
i kept my old one with a perruno cat,megalodoras irwini,silver arowana,bichirs and a couple of other fish.
it ate a delhezi,a SB senegal and a nandus nandus.
all were smaller than the gulper.