Docile to we human's that is
.. Some fish aren't meant for the "Community tank". Cichlid's, certain Barb's, and most fish considerably larger than those they share an aquarium with aren't a good idea. Not to mention putting the faster smaller "fin nipper's" in a tank with a slow exotic isn't such a great idea either... Been MANY years since I managed the tropical fish center if a pet chain around here...Loved Aquaria (both fresh and Salt) as a HS kid... Had ALOT of tanks setup...
Yet was never tempted to get the Red Pirahna, mistakenly (deliberately) labeled as a Pacu.. a few of my classmates needed for "drool" factor...