Hello Harry,
Blue Carp, do you mean Black Carp (speci on the photo)?
We have 4 foreign carps: black carp, grass carp, bighead carp, and silver carp. All originally imported from China, now natives in Japan. They all grow quite large when condition is met. Large and slow flowing rivers and inlets such as Tone River is known habitat for them.
Do you use bait, lure, or fly?
These guys are going after giant suckers.
http://blogs.yahoo.co.jp/ooedo0051
There is a guy who fishes carp on regular basis on fly and fortunately caught grass carp on fly. Please see the bottom of this page:
http://www.level4.jp/carp_fly/othe.htm