Eggs are found in all female fish, but most fish roe isn't especially distinguished for human consumption. (Although speckled trout roe is much liked by some people, including me.) Caviar is fish roe that's been separated into individual eggs, then treated with salt to preserve it. The less salt, the better the quality. The world's greatest caviars came from several species of gigantic sturgeon that live in the Caspian Sea. But those fish are nearing or beyond the state of endangerment. You cannot buy beluga caviar legally anymore. And the other Caspian caviars are fantastically expensive. But we have an excellent local caviar, from a primitive fish that lives in rivers and bayous around Louisiana. Ichthyologists call it a bowfin. The local name is choupique (pronounced "shoe-pick"), from a Native American word that means "mud fish." The process of making caviar from the choupique's roe was developed by a family living in the Atchafalaya Basin. John Burke, a young failed oilman, thought it had possibilities and marketed it under the name "Cajun Caviar." It's not just good for what it is, but a first-class caviar by any standard. The grains are very black and on the small side. The flavor is so good that very little salt is used in its manufacture. I wouldn't hesitate to serve it whenever caviar is called for. It is much liked by local chefs for its flavor; the local aspect is a bonus. Choupique caviar is not constantly available. The first few months of the year is the best time to buy. You have to go to a gourmet shop or high-end grocer to get it. Or you can go to a restaurant--the Bourbon House, where they serve dollops of choupique caviar atop raw oysters.
