In the movie "28 days"http://en.wikipedia.org/wiki/28_Days_(film) an alcoholic wanting a relationship is advised to first keep a plant. It's been a common recommendation for those in recovery to have a pet but in the movie the humor was that this fellow was so self absorbed that he was recommended instead to start with a plant. Pets take many of us out of ourselves.
I've often had fish in my waiting rooms because they have a calming distracting influence that prepares people for discussing the more anxiety provoking aspects of their lives.
Not surprisingly my dentist has a wall size tank which he uses for the same reason, but clearly as a dentist he needed a bigger tank and bigger fish.