Combine mayonnaise, mustard, pickles, capers, green onions, lemon juice and parsley. Mix well. Add salt and pepper. Chill before serving to allow the flavors to marry.
Combine cornmeal, flour, salt, cayenne pepper and garlic powder.
Coat catfish with mixture, shaking off excess. Fill a large, heavy skillet half full with vegetable oil. Heat to 350° F.
Add catfish in a single layer, and fry until golden brown, 5 to 6 minutes, depending on size.
Remove fish from oil, and drain on paper towels.
Preheat oil to 350° F. Combine cornmeal, flour, sugar and salt. Mix well. In a separate bowl, combine jalapeños, onions, buttermilk, egg and cheese. Add to dry ingredients, stirring until just moistened. Cover with plastic wrap, and let rest for 15 minutes. Drop batter by heaping teaspoons into heated oil, and fry, turning hushpuppies to cook evenly, until golden brown.
Serve with Hushpuppies and Tartar Sauce.