I have 3 Black tips (Colombian Sharks). Small, only about 2.5 inches so far. When they get excited they sometimes display this behaviour, but as mentioned, if you have caves and other things for them to swim amongst and hide in they calm down quickly. They are extremely active fish though. Mine love playing a game where they swim back and forth, or up and down in a corner, bumping and jostling each other all over the place. I currently have them in a 10 gal, but not to worry, a 50 gal is being setup as we speak just for them, and then when they outgrow that, I'll be setting up a 120+ gal for them. Their only tank mates are one common pleco and 2 red claw crabs. Be careful when you first start, I'm quite new to fishkeeping, and a lot of LFS's don't bother giving you good advice, if any at all. I did some research on tank conditions, but in my excitement didn't do enough on fish before I purchased. Now that I have I'm adjusting for their needs. Try and resist the newbie's urge to overcrowd a tank. Less and simpler is better (man what a bad sentence).