The moat was originally designed as part of an exercise program. It is more of a large endless lap pool, with circulating pumps that keep the water going in a circle around the castle. And yes, the tilapia have been breeding in there. Fortunately, the plesiosaurs keep them from overrunning their environment.
Exercise otherwise is a bit of a lost cause, in Habitats that are rotating for artificial gravity at the Mars level of .34 gees.
Our muscles grow weaker, but at least it's easier on old bones and joints.
Climbing has become a popular activity. At these acceleration rates, the athlete feels much stronger.
But the primary physical activity comes from being a member of the canopy repair crews. They're organized into teams, like a sports franchise. Awards and certificates are given for fastest on the scene and quickest repairs, and so forth. The competition is intense and the pace is very physical.
If you don't mind getting a crick in your neck, you can watch them train. They do it every day, right over our heads.
I usually have a crick in my neck. Happy to watch them!
Serious question on the above topic. The spaceship "Discovery" in "2001: A Space Odyssey," used a rotating area to simulate gravity of (seemingly) 1g throughout the flight to Saturn. Wouldn't that require the same expenditure of energy on the part of Discovery as simply propelling itself at 1g toward Saturn? The rotational force isn't "free," right?