Any guide book will tell you to visit Tsukiji market The reason I'd not been before - its recommended you get there at 5am. Well, Ayesha and I made it, and I have to say it was definitely worth it. I didn't think it would be possible to catch that amount of fish, and this was just an average day's trading.
Plenty more pictures on this link
2,500 tonnes of fish worth USD23million are sold daily.