Stir together buttermilk or yogurt and hot sauce; brush on catfish and allow to marinate for 10 minutes. Coat catfish lightly with cornmeal and sprinkle with salt and pepper, to taste.
Melt butter and olive oil in a nonstick skillet over medium high heat. When skillet is hot, saute catfish about 3 minutes on each side, turning only once, until golden and crisp. Serve immediately, garnished with lemon wedges and with tartar sauce as accompaniment.