For the ceviche: Place the shrimp into a pot of salted water. Place over medium heat and cook until just starting to turn opaque, 2 to 3 minutes. Drain before adding to the rest of the ceviche.
Meanwhile, dice the mahi mahi into 1/4-inch pieces and set aside in a large nonreactive bowl.
Peel the celery and place in a food processor with the lime juice and orange juice. Puree until smooth and set aside. Add the celery puree to the fish and sprinkle with the cumin, cayenne and some salt and black pepper. Add the shrimp and stir well to incorporate. Cover and chill the ceviche in the fridge for 15 to 20 minutes. The shrimp will turn pink and the fish will turn white when cooked. Toss with the cilantro just before serving.
For the tortilla strips: In a large cast-iron pot over medium-high heat (or in countertop fryer), bring the oil to 325 degrees F. Add the tortilla strips and fry until golden brown, 3 to 4 minutes. Remove to towel-lined dish and drain. Season with salt.
To plate: Spoon the ceviche into a serving bowl and garnish with the tortilla strips and lime wedges.