ABSTRACT
The eel is known as a bottom dwelling fi sh, but it has a well-developed swimbladder, which is an established model for the analysis of swimbladder function. The swimbladder originates as an unpaired dorsal outgrowth of the esophagus and in the adult stage is a gas-fi lled sac located below the vertebral column. Although the swimbladder of some teleost fi shes may serve respiratory functions or can be important for sound production, it primarily is seen as a buoyancy organ. As a buoyancy organ this structure has attracted attention since more than two hundred years (see Alexander 1966, Dorn 1961). Although the eel swimbladder has a somewhat peculiar structure, the presence of a particularly impressive ‘Wundernetz’, the rete mirabile, which is a fantastic countercurrent system allowing access to both sides of the rete, may explain why it has been extensively studied in the European eel Anguilla anguilla. Its structure had already been delineated in 1882 (Pauly 1882), but it was described in detail almost 100 years later (Dorn 1961).
