I first visited Duisburg in October 1980 (and have been a number of times since).
On that original visit I saw beluga, Commerson’s dolphin and Amazon river dolphin, all for the first time. (Duisburg is still the only place where I’ve ever seen Amazon river dolphin.)
In addition to the three species of cetacean, that visit was also the first time I saw fossa and giant otter, so it was a very memorable trip; it’s frightening to think that it was 29 years ago.
I missed the tucuxi dolphins in Duisburg, but I have seen them at both Nuremberg and Munster zoos. (I think that they were actually the same animals that were moved from Nuremberg to Munster, but I’m sure that somebody will be able to confirm that.)