First he was asking if they have a type of fish. Then, he was asking for a "swimming sashimi" (sashimi = raw fish). Usually this means a fish that has been cut up and is on the plate live. All that happened here was that instead of the fish being live on the plate, it was live in the water. This is pretty common in Japan (live on the plate, not common for it to be in the water). The announcer said something like "he took a single fish, grated some fresh wasabi, this place is pretty famous for its good service." Anyway, he was surprised when he saw it because it wasn't live on the plate, and questioned its authenticity, until he saw it in the tank. In the crazy negative flash scene the announcer said, "and what the heck is that in front of him!?" Then he shouts "It's swimming!" The chef said that he got the idea from a manga that he read when he was a kid.