If you decide to visit the fish market you need to be accompanied by someone who has close ties with the fish market, or you will unlikely see the backyard. The market closes on the 31st of December and reopens on the 6th of January.

In any event here are some details:

http://www.shijou.metro.tokyo.jp/pdf/english/tsukijiguide.pdf

http://www.jnto.go.jp/eng/pdf/special/tsukiji.pdf

http://www.tsukiji-market.or.jp/tukiji_e.htm