A couple of mine did it today, for a couple of hours: chased each other tails in a circle. The participants, strangely, were smaller kubotais, the larger ones ignored it. Unclear what caused the chase: I've not been adding any new fish to the tank for a while, nobody died either, so they should have had no reason for hierarchy fights. (I've seen several fights like this when the tank was set up originally, but none for a few months.)
The video quality is low after being compressed from 180mb->3mb (the original avi was quite good but too large to upload ).
Probably, except that there is no hierarchy in this tank I could ever see: five smaller kubotais are suppressed by the presense of six clowns. I don't think there is even an alpha kubotai among the five.
My other three kubotais that share another tank with five yoyos do have a clear hierarchy: the largest kubotai rules. Incidentally, he is smaller than any of the yoyo's right now, but is considerably more determined. No fights either; simply occassionally -- like every few hours -- he chases the other botias, concentrating on smaller kubotais. A pretty mean fellow, but with nice black (almost as good as yours).
Nice show! Funny to see the other fish acting as if nothing is going on.
I have not witnessed a single fight in my tank between 5 yoyos, 2 rostrata and a single striata. All are under 3 inches still. Maybe soon. For now it seems like they're all pals.
Yoyo's are not as serious about dominance as Kubotai's; you see that both in mine and Vancmann's tanks smaller Kubotai's rule over larger yoyo's. The Kubotai fight on the video, btw, is non-contact --- they chase but do not touch each other. The very first time I saw it, it was scary: one of the Kubotai's was totally white from stress, and then he dissappeared for a day to recover. Yesterday, it was a little less intense.
I think I mentioned that I saw Kuhlis doing nearly the same too, but this is really uncommon. Clowns and Yoyos are not capable of this show....maybe your rostratas are.
BTW, if you want full-quality video of the fight, I'll be glad to send a CD.
Check your PM for some unusual loach you may want.