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I don't have a digital camera (yet) to take snaps of my catfish, but I'm hoping someone can help me out IDing one of my cats.

How can I tell the difference between a "Arius graeffei" and a "Arius berneyi"

... both species look identical.

Thanks in advance.

The only way you can reliably tell them apart is to look at the palatal tooth patches (the patches of teeth on the roof of the mouth).
Not possible with a live fish, I think.

Does it look like this?

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Don't think so. Australian ariids tend to have broader, flatter heads.

It sort of looks like that... but yeah, this aussie cat of mine has a flatter/broader head... he's also a bit darker/blacker... the pet-store guy said they are called "Salmon-tailed Catfish".

i live in australia. after years of observation, the only external ways of telling the difference that i can see are:
a) a. berneyi have sharper points on the caudal fin whereas a. graeffei tend to be rounded. even so the difference is only slight and you need to have the fish side by side to notice.
b)a. graeffei are black in colour. a. berneyi are more a dark silvery-brown. once again you need to see them both at the same time to notice.
c) size. in captivity a. berneyi max out at around 10inches. a graeffei get to 24inches or more.
both species need lots of swimming room, even compared to other catfish of a similar size. they're very active...= a big tank.

It's a Graeffi then. He's jet black and has rounded off fins. I actually got the ID yesterday cuz I talked to the manager of the aquarium and he does all the fish orders. He showed me a big book on catfish with colour photos of native australian cats and showed me the differences there.