Yes Ocean World can be booked directly through your holiday Rep. However, they do fill up. Depending on when you are coming, it is better to book in advance, specifically the dolphin swim!
Here is their website:
Ocean World in the Dominican Republic | Dolphins Sealions Sharks Stingrays Tigers Tropical Birds Rainforests Snorkeling | Cofresi Beach,
The night tour is a fabulous buffet dinner, sea lion and dolphin shows, good dance show and casino. I enjoyed the entire evening.