Here is my first Black Arowana I raised from 3" to 24" in a 230 gallon tank. I then lost it with some other fish when I forgot to turn my filters back on after feeding my fire eel bloodworms! This was back in November of 2007. (on a side note two of the clown loaches you see in the pic were 14yrs old and the rest 8yrs old..ouch!)But I came back with a vengeance right away and bought four more black arowana and now you've seen the pair I kept! Now you know the rest of the story....LOL
From the pix it really looks like they are doing the mating dance.
I have exactly the same situation with an asian and a silver ( as I described in another thread ).
I know my asian is the male because it grunts like a failing pump and wiggles like crazy when he is rubbing alongside the silver ( which I surmise is a female ).