A thin membranous, sometimes alveolated sac in the dorsal portion of the abdominal cavity. Contains a varying mixture of gases, not identical to the composition of air. May be one, two or three chambered. May be connected to the gut by a tube, the ductus pneumaticus (then called physostomous) or unconnected (then called physoclistous).
Comment:
[function-note] "May function as one or more of: hydrostatic organ, sound producing organ, sound receptor, respiratory organ"; [homology-note] "Lungs had already developed as paired ventral pockets from the intestine in the ancestor of Osteognathostomata. (...) In actinopterygian fishes, apart from Cladistia, the ventral intestinal pocket migrates dorsally and becomes the swim-bladder, a mainly hydrostatical organ (reference 1); Comparative transcriptome analyses indicate molecular homology of zebrafish swimbladder and Mammalian lung (reference 2).[well established][VHOG]" xsd:string {date_retrieved="2012-09-17", external_class="VHOG:0000310", ontology="VHOG", source="ISBN:978-0198566694 Schmidt-Rhaesa A, The evolution of organ systems (2007) p.210, DOI:10.1371/journal.pone.0024019 Zheng W, Wang Z, Collins JE, Andrews RM, Stemple D, Gong Z, Comparative transcriptome analyses indicate molecular homology of zebrafish swimbladder and Mammalian lung. PLoS One (2011)", source="http://bgee.unil.ch/"}; [taxon-note] "Found in Actinopterygii. Often lacking in bottom fishes"