I grabbed a blood orange, a ruby grapefruit and lots of limes to make this version, hence the pinkish purple hue to the fish. But lime and lemon are traditional, so don't feel the need to splurge on other citrus. Make sure at least half of the marinade is lemon or lime, the other citrus doesn't have enough acid to cure and thus transform the fish from raw to cooked.
My ceviche marinade always includes several cloves of garlic, at least half a jalapeno (deseeded and deveined if you like less heat) sliced in rounds, and some cilantro. But you can limit it to just citrus juice, if that is what pleases you.
Usually ceviche is served with chips, but here I wanted more fish and less chips, and a tostada worked perfectly.