Cut the whitefish into cubes no bigger than 1.5".
Place the fish in a glass bowl, and fully submerge them with the juice of the limes. Cover tightly, and refrigerate for at least 4 hours.
Remove the fish from the fridge and drain the liquid. Add 1/2 cup of thinly sliced red onion, about 1/2 of a tomato, the diced jalapeno, and cilantro (if you like cilantro).
Salt to taste, and serve with tortilla chips.