I spent about an hour last night searching through fish from the gulf of mexico and never found anything that sounds like what you caught. They only ones that were scaleless and had 6 fins were all species of Shark.
SHARK, WHITESPOTTED BAMBOO (Chiloscyllium plagiosum) LONG SLENDER BLACK AND WHITE STRIPE BODY
SHARK, BROWNBANDED BAMBOO (Chiloscyllium punctatum) LONG SLENDER BODY. JUVENILE IS BLACK AND WHITE STRIPE.