Seki - That bridge is a source of some trouble as Emilia has claimed it and whenever she is there she will flare at whoever else comes near it and chase them out. But when she's gone the others will swoop in and play around it XD It's always fun to watch and see whose making it their little home when she's hanging out at the top.
Kev - You should! It took me awhile to finally start one up too, but once I did I was completely hooked on all of my girls. They've got those wonderful personalities and it's awesome to watch them swimming around together. Love my sorority tank.