The freshest fish here are the ones you catch yourself
"Zauo" is an amalgamation of the kanji for "Sit" and "Fish", which is basically the entire concept of this themed restaurant chain in Japan.
Unlike those in most seafood restaurants, the aquariums in Zauo are not just for show. When you enter Zauo, you're given a fishing rod and some bait, and are told to catch your own dinner. You sit on a giant boat, surrounded by an equally impressive aquarium full of fish.
The aquarium is full of a variety of pescaterian delights ranging from red snapper, to mackerel, to sharks. If it's in the aquarium, it's fair game for you to catch. Whether or not you can catch the more delectable fish depends more on luck than skill.
When you eat depends on how well you fish, and how you want your fish prepared. You can get your fish grilled, fried, steamed, and boiled, but the freshest option is to have your fish raw, sashimi style.