Rick Bayless has some recipes on his cooking program on PBS; he lets the fish or other seafood sit in the lemon or lime for sometimes just a couple of hours.

Scandinavians aren't the only ones who "cook" fish in acid (vinegar or citrus) and the peppers and herbs in the Mexican dish make it all the more appealing. A typical serving is to use a large tortilla chip, or use a tostada (cooked corn tortilla that is crisp) and put on a layer of sliced avocados or spoon on a generous helping of guacamole, then spoon the ceviche over the top. Mmmmmmm! Such a nice summertime meal. (I get it in regular Texas restaruants, Mexican restaurants, and general Hispanic groceries: Wikipedia says ceviche/cebiche/seviche/sebiche originated in Peru.)