Development of the swimbladder in the European eel (Anguilla anguilla)

Abstract

The swimbladder of the adult eel, Anguilla anguilla, with its bipolar countercurrent system, the rete mirabile, is a widely used model for swimbladder function, but very little is known about the development of this swimbladder. Our histological studies on the developing swimbladder revealed that during metamorphosis the swimbladder becomes present as a dorsal outgrowth of the esophagus. It is filled with surfactant, and gas was not detected in the swimbladder. In the young glass-eel, the epithelial (gas gland) cells of the swimbladder are columnar, but do not yet have the typical basolateral labyrinth established in adult animals. Few blood vessels are found in the swimbladder tissue, and the submucosa is present as a thick layer of connective tissue, giving a large diffusion distance between blood vessel and swimbladder lumen. Within the next 2 or 3 months of development, gas gland cells develop their typical basolateral labyrinth, and the thickness of the submucosa is significantly reduced, resulting in a short diffusion distance between blood vessels and the swimbladder lumen. The first filling of the swimbladder with gas is observed while the gas gland cells are still in a poorly differentiated status and it appears unlikely that these cells can accomplish their typical role in gas deposition. The presence of small gas bubbles in the swimbladder as well as in the ductus pneumaticus at the time of initial swimbladder inflation suggests that the swimbladder is filled by air gulping or possibly by taking up gas bubbles from the water.

Expression of a lung developmental cassette in the adult and developing zebrafish swimbladder

“…A BLAST search of the Danio rerio transcriptome returns no matches at either the RNA or protein level for surfactant protein C, so we have concluded that this gene is not present in the zebrafish genome and therefore have not attempted to include it here. Other studies have found that surfactant proteins A and B are present in the swimbladder during development, and are important for swimbladder inflation in some taxa [Anguilla rostrata (Zwerger et al 2002) and Stizostedion vitreum (Marty et al 1995)]. Though initially it was unclear if this surfactant was expressed in swimbladder tissue or diffused from another structure, Prem et al (2000) showed that these surfactant proteins are in fact secreted from the gas gland cells of the adult swimbladder, in eels (Anguilla rostrata) and perch (Perca fluviatilis).…”

Ecology of Anguilliform Leptocephali: Remarkable Transparent Fish Larvae of the Ocean Surface Layer

“…Eels do not develop a swim bladder until after metamorphosis near the end of the glass stage, based on observations of an anguillid (Zwerger et al 2002), so their lipid content, high water content, and almost complete lack of ossified structures may contribute to their buoyancy (Pfeiler 1999). A comparative study of the specific gravity of 25 taxa of 7 phyla of zooplankton and 6 taxa of leptocephali found that leptocephali were among the species with the lowest specific gravities and highest buoyancies ).…”

An evaluation of indices of gross pathology associated with the nematode Anguillicoloides crassus in eels

“…The ‘true’ biological value to investigate is here tentatively assumed to relate to the loss of internal swimbladder volume. The eel swimbladder is an organ involved in many important functions such as buoyancy control, gas exchange, absorption and secretion (Zwerger, Nimeth, Würtz, Salvenmoser & Pelster 2002; Tesch 2003), so that any reduction in the lumen gas volume is expected to severely impact on the general metabolism and physiology of the fish (Würtz et al 1996; Palstra et al 2007).…”