This is part of their territorial behaviour.
I think it basically means, "Don’t come any closer" or "do not cross this line"
In my tank, the M.johanni and M.auratus are doing the same thing with the Johanni being the number one and the Auratus the number two in rank. They allow each other to swim freely in the tank but sometimes when they come to close, they rush back to their territory and start defending their boundaries.
They seem to show this threatening behaviour only towards each other and in that particular area. Some others like the Yellow Lab or M.estherae, especially the young ones, are displaying this tug and tow-game more often but unlike the Johanni and Auratus, it happens not in a specific area and most of the times it ends up in a short fight. So in this case, I would say it’s more like measuring strength and trying to establish their place in the hierarchy.
This is based on my own conclusions from what I have seen in my tank.
Apart from lots of articles on general territorial and breeding behaviour, I couldn’t find anything on this particular behaviour on the net. Sorry I couldn’t help you there, perhaps someone else can.
Jimmy
