title: Different on the inside: extreme swimbladder sexual dimorphism in the South Asian torrent minnows.
abstract: The swimbladder plays an important role in buoyancy regulation but is typically reduced or even absent in benthic freshwater fishes that inhabit fast flowing water. Here, we document, for the first time, a remarkable example of swimbladder sexual dimorphism in the highly rheophilic South Asian torrent minnows (Psilorhynchus). The male swimbladder is not only much larger than that of the female (up to five times the diameter and up to 98 times the volume in some cases), but is also structurally more complex, with multiple internal septa dividing it into smaller chambers. Males also exhibit a strange organ of unknown function or homology in association with the swimbladder that is absent in females. Extreme sexual dimorphism of non-gonadal internal organs is rare among vertebrates and the swimbladder sexual dimorphisms that we describe for Psilorhynchus are unique among fishes.
authors.affiliation: Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843, USA kevin.conway@tamu.edu.
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Conway
authors.affiliation: Natural History Museum, Cromwell Road, London SW7 5BD, UK.
authors.forename: Ralf
authors.initials: R
authors.lastname: Britz
authors.affiliation: Department of Biology, Southeast Missouri State University, Cape Girardeau, MO 63701, USA.
authors.forename: Dustin S
authors.initials: DS
authors.lastname: Siegel
mesh_terms: D000400:Air Sacs / Q000033:anatomy & histology*; D000818:Animals; D003530:Cyprinidae / Q000033:anatomy & histology*; D005260:Female; D008297:Male; D010802:Phylogeny; D045483:Rivers; D012727:Sex Characteristics
keywords: Psilorhynchus; Teleostei; histology; morphology