The ductus pneumaticus (from Latin ductus - duct, and Greek πνεῦμα - breath, air), sometimes also referred to as the swim bladder duct , is a connecting duct between the swim bladder and the foregut of bony fish . Since the swim bladder arises as a protuberance of the foregut during embryonic development , a ductus pneumaticus is originally present in all fish with a swim bladder.
Fish in which the ductus pneumaticus persists in later development are called physostomes . With them, the degree of filling of the swim bladder can be partially regulated via the ductus pneumaticus, which can be closed by muscles . In some species, thanks to this connection to the outside world, the swim bladder can also take on a respiratory function by swallowing air . The distal part of the pneumatic duct is often equipped with a capillary network , which also enables gas exchange with the swim bladder.
Fish in which the ductus pneumaticus regresses or does not function at all are called physoclists . In these, the aforementioned capillary network is particularly well developed and takes on the function of filling the swim bladder solely as a gas gland (red body).
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