Development and function of the swimbladder‐inner ear‐lateral line system in the Atlantic menhaden, <i>Brevoortia tyrannus</i> (Latrobe)*

Abstract

The swimbladder‐acoustico‐lateralis system of the Atlantic menhaden, Brevoortia tyrannus , is described and compared with that of the Atlantic herring, Clupea harengus . The system develops in the larva at a much earlier stage than the herring, being functional by about 2 mm tl. The volume of the gas‐filled pro‐otic bullae is five times that of the herring, and the gas ducts to the swimbladder, instead of being short and separate, are three times the length and join to form a common duct well in front of the swimbladder. The menhaden swimbladder is baggy and totally compliant when subjected to pressure changes. There is no toughened anterior end as in the herring, but the swimbladder is steeply angled in the body cavity, causing gas to collect at the anterior end after a pressure increase, unless the fish is diving very steeply. The guanine content of the swimbladder is comparable with that of the herring and makes the wall very impervious to gas diffusion. When subjected to quick pressure increases and decreases, the pro‐otic membrane returns to its flat position with a time constant of 31‐44 s. Very large quick pressure changes of about 3 atm burst the pro‐otic membrane in adult fish but not in larvae.