It does look rather like it brakish will pose a problem eventually. Could it be a salmon tail catfish? they look basically identical. I only suggest it as I live in oz and apparently there native.
Either Arius thalassinus, Arius berneyi, Arius graeffei, or Arius leptaspis. All different catfish but they all go by samontail catfish. The thalassinus grows HUGE! (73in.)