What are my Gastromyzon doing?

[Mike_Noren]

I have a bunch of Gastromyzon ctenocephalus, and two of them are acting weird.

One of them has his nose to the cloacal region of the other, and keeps pushing the other fish sideways in a circle. Round and round and round - they've been doing this for at least a couple of hours.
One of them has gone completely white, the other is normal-colored. They also did the same "circling" down on the sand; then both rose up on the their pelvic fins in an apparent attempt to look bigger.

I'm guessing this is some kind of aggressive/dominance behavior... but they've been at this for hours now? Is this normal?

[Jim Powers]

That's normal. Most of the time the battles last a short time, but sometimes they can last for hours. Just sit back and enjoy the show.

[Mike_Noren]

Thank you.
Also, they seem to have figured out who's the boss now, so the circle-dancing has temporarily stopped.

[Graeme Robson]

Indeed temporarily stopped.