Odessa Barb Behaviour

[Musahi]

Hi there. I think this is the right place to ask a question about Odessa Barbs. Apologies if I'm wrong. My question is about a certain behaviour that I've noticed on occasion. I have 5 Odessa's, but I've only noticed 2 of them doing this. I have a barrel ornament, and what they're doing is swimming really fast and diving/scraping their body against the outside of it, in an upward sweep. In no way do I think they're ill. Their skin looks perfect, their colours are bright, they're not sluggish or acting unhealthy in any way. They seem to be thriving, in fact. I think this is a behaviour thing, but I'm wondering what this behaviour is all about? Perhaps mating behaviour? Or dominance? I notice my tiger barbs have a ritual of going vertical, nose pointing down, slightly arching themselves and fluttering their tail fin. They do it most when they're right next to another one of their kind. I've read this is a typical behaviour of theirs so I'm not worried. I find it interesting watching the things they all do. But this Odessa diving behaviour is most strange. Oh and another question..is it normal for a Pleccy to be so shy? He hides away in the barrel most of the time. He comes out occasionally, but if I move in the room he scurries away back into the barrel. I know they're nocturnal so do most of their activities when I'm fast asleep, but my friends Pleccy's are all out and about, stuck to the glass etc, not bothered by anyone in the room. Anyone got any ideas? Thanks!