Caviar is the roe (or eggs) of the sturgeon. These are very highly salted, which helps to preserve and flavor them. The three main types of caviar - beluga, oscietra and sevruga - come from different varieties of sturgeon. These originate mainly from fish in the Caspian Sea that are over 15 years old.
The most expensive caviar is from the beluga, as only about a hundred fish caught each year. The eggs are fragile and vary in color from light to dark grey with a white spot. Sevruga is small dark grey, with a light, sweet taste.
Nutty-flavored eggs from the oscietra are small and black when the fish are young - but become larger and golden as the fish ages.
** Asian Recipes