Via Shedd Aquarium, which writes:
While some of our species are scary enough to create a spooky atmosphere on any given day, Shedd Aquarium trainers surprised beluga whales, penguins, sea otters, sea lions and dogs with a few tasty fall and Halloween-themed enrichment toys and fish-flavored frozen treats to get into the spirit of the holiday. Enrichment activities aren’t just for fun but are an important part of animal care at the aquarium, creating opportunities for the animals to interact, play and explore.