Cut orange in half horizontally and section it as you would a grapefruit; do this over a bowl to capture all its juice. Remove seeds and combine flesh and juice in bowl. Repeat with grapefruit and lemon. Stir in cilantro, chopped habanero, and salt.
Put oil in a nonstick or cast-iron skillet over medium-high heat. A minute later, add fish, skin-side down; season top with salt. Cook until skin begins to crisp, 3 or 4 minutes, then transfer to oven. Cook another 3 or 4 minutes, or until a thin-bladed knife meets little resistance when inserted into thickest part of fish. Serve fish with Mayan citrus salsa (xec), immediately.