Beluga

This is a big fish, and so its eggs are bigger and more expensive as others.

The normal weight comes from 40 to 300 kgs. ( although sometimes it can be more than  1000 kgs ) and the caviar that is obtained is a 15 % of its weight. 
Its colour is gray, being more appreciated the darker it is. It always comes in blue cans.
The best world quality caviar comes from Russia and Irán.