The chain offered a Spicy Cajun Fish sandwich back in 2008, which was basically their Classic Fish Sandwich (now called the "Crispy Fish Sandwich") but with a spicy Cajun tartar sauce in lieu of regular tartar sauce.
I was told by an Arby's representative that the Cajun Fish Sandwich is a new sandwich. Be that as it may, the sandwich certainly sounds like the previously offered seafood sandwich; it consists of a crispy fish filet, Cajun tartar sauce, and shredded lettuce on a toasted sesame bun. What may be considered new is that, like Arby's current fish sandwich, the Cajun Fish is also available on flatbread and as a King's Hawaiian Deluxe sandwich (which replaces the sesame bun with a King's Hawaiian bun and adds tomato as well as a slice of cheese).
Photo via Arby's.
