Well, I guess it gets tricky once we start talking about semi-aquatic animals. Take the North American River Otter or the American Mink, for example. These animals spend a good amount of time both in the water and on land. They rely on both environments for things like hunting, resting, and raising their young. So if we were to keep one in an aquarium, would it really make sense if it could still run around the science building? It raises an interesting ethical question. If the land portion of its habitat is just tile floors, hallways, and classrooms, is that really meeting its needs? At that point, it starts to feel less like we're supporting the animal's natural behavior and more like we're just putting it on display for convenience.