narauki aoki is a diver. every day he has a different interest. he's retired.he goes diving a lot now. as much as 100 days a year. the sound of a hammer is enough to attract the finish to this spot where a camera has been set up. ten years ago aoki noticed that sea bream reacted when he broke shells with a hammer. after returning to the same place over and over again, he eventually managed to get the fish to eat out of his hand. then six years ago he started to train them to swim through hoops using food as a reward. >> translator: it's taro ichiro goda isn't here. i recognize them by their faces. >> reporter: taro first approached aoki seven years ago. ichiro seems to like showing off his moves. and this is big old gonta. he's recognizable by the scar on his head. gonta was the first of the black sea bream to react to aoki's hammer ten years ago. >> translator: they're really lively today coming back again and again to eat my glove. it's like i'm playing with children. >> reporter: tetsuya imino is is a marine biologist. he's never heard of a black sea bream e