It used to be pandas. The sex-life (or lack of it) of Chi-Chi and An- An put them on the front pages alongside Nureyev and Fonteyn. If pandas had had a better agent it could all have been different. A couple of babies would have clinched their star status well into the millenium. Instead, they lost out to a smoother operator, the dolphin.
Dolphins have been kept in tanks for our amusement since 1938. Naturally gregarious, almost tarty animals, they show no particular signs of disliking their paddling pool. Unless you count disease and premature death.
The alternative to the Dolphinarium is to put up a sign saying "Free Fish All Day" and see who turns up. These dolphins are tame only in the sense that your cat is tame: unlimited sardines and heavy petting will guarantee regular appearances, but they could do a runner at any time. Meanwhile, the Dolphinarium keepers argue that they are learning about behaviour. Teach dolphins enough sign language and they can tell you whether there's a frisbee in the pool. What dolphins make of a species that needs this question answered is no doubt part of their own study of human behaviour.