 The swimbladder in the Sillaginidae is either absent, poorly developed, or highly complex with anterior and lateral extensions that project well into the caudal region.A unique duct-like process is present from the ventral surface of the swimbladder to just before the urogenital opening in most species.The presence and morphology of each species' swim bladder is often their major diagnostic feature, with McKay's three proposed subgenera based on swimbladder morphology alone.