Roe and Caviar are both related in that they are both referring to fish eggs, but there are still some differences between the two. Roe simply means the sperm of certain fish, and it also means the eggs of fish. Caviar differs from Roe because it is a roe that has been processed with salt so as to prevent it from getting spoilt. In other words, caviar is the roe of the sturgeon or other large fish. After a roe is salted, it is stored in a tin for preservation.
There is another difference when you consider their color. Both have different bright colors, and that's why you can easily differentiate between the two. Roe has an orange color, while caviar has a silver or black color. In terms of price, caviar is very expensive compared to roe. Roe can be gotten from certain fishes, and that's why they are readily available in most restaurants.