Pour one cup of hot sauce over catfish filets and marinate overnight.
Heat fryer oil to 350° in deep fryer.
Remove filets from marinade and shake off excess hot sauce.
Whisk eggs and water to make egg wash. Combine panko and half cup of flour for final coating. Dredge in flour, then egg wash followed by panko then cook in fryer until golden brown. Remove from fryer and place on towel to drain off excess oil.
Whisk together mayonnaise, horseradish, lime juice, lime zest, cilantro, salt, black pepper, and hot sauce. Reserve refrigerated for service.
Place one filet per serving on plate with a side of sauce.