This is a Peruvian ceviche which uses tilapia. If you can't find tilapia, use any other light white fish.
I am from Peru and our typical Peruvian Cebiche uses no potatoes, no celery, no cumin. We basically cut the fish into 1/2-inch pieces (I love Bass or Tilapia), add salt, pepper, chop fresh cilantro, a bit of garlic and lime juice (about 8-10 limes). Fish has to be cooked in the lime juice. You can add shrimp/clams/octopus, it's optional. My family loves the original Cebiche, fish only. Add some fresh Aji Amarillo (Peruvian chili, looks like the Habanero but its taste is amazing and unique) or Aji Amarillo paste - you can buy them at any Latin Market - and mix it with the lime juice. Add some lettuce on the side as well as peeled & cooked sweet potato (just a slice per person) and add some corn on the side as well (about 1/4 cup. Don't forget to add the onion (I use red onion - julienned red onion). - 16 Dec 2011 (Review from Allrecipes USA and Canada)
I laughed so hard when I read that a reviewer sauteed this!! Ceviche is ONLY "cooked" in the lime juice and is not placed over heat of any kind. I've never seen white potato served in a cevicheria...but the sweet potato is a must. The onion should be sliced and this should NOT be eaten over crackers if you want authentic. Usually it is either plain fish (bass is more common than tilapia) or a lot of mixed sea creatures you won't find for sale in the States. Like a lot of Peruvians, I prefer the pure fish version. - 06 Mar 2009 (Review from Allrecipes USA and Canada)
This was so delicious! The only changes made were to add cucumber, though I don't think it was necessary after having tasted it. The only changes I would make in the future would be to add more habanero because I like it spicy. Also great the next day with pita chips. *edit: I noticed that another user actually cooked the fish by sauteing it but it should be noted that in a ceviche recipe the fish is "cooked" through the lime juice marinade. It requires no heat. I hope this helps! - 24 Jul 2007 (Review from Allrecipes USA and Canada)