However, I would consider the following before deciding that Sea World gets all the "bragging rights," as it were.
There is an oceanarium still in existence today (thriving, in fact) that has been around a lot longer. Although the idea of captive marine mammals dates back over a century, the first practical oceanarium (as in one that did not mean quick death for its inhabitants) first opened in 1937, in the form of Marineland near St. Augustine, Florida.
That makes them ... let's see ... Ah! Seventy-two. That also makes them the oldest surviving ocean park in the United States. ;-)
I would point out that while Sea World may get all the publicity, and consider themselves to be a tremendous success in many ways, none of their parks (nor very many others, for that matter) have come close to Marineland's records for something I think is far more important than any thrill-ride or tackily-scripted show: The successful long-term survival of captive dolphins.
I'm referring, specifically, to one of Marineland's female bottlenose dolphins, name of Nellie. She just turned 56, which in human years would be about 104. And she's still going strong!
You don't have to take my word for it. Read for yourself.
What a fascinating park Marineland is! They never needed roller coasters or "theme" rides to survive into their seventh decade, nor has their considerable and obvious success stemmed from bizarre stage shows that, as someone once said to me, look like a cross between Cirque du Soleil (did I spell that right?) and the London Philharmonic.
Sea World SD may indeed see their 90th. Who can tell? However, although I'm pretty sure I'll be gone before then (as I think many of us will), I would be very curious to see if they can keep going the way they're going and reach their 72nd (or even their 46th).
I'm content to let history itself be the judge.