Swimbladder form in clupeoid fishes

The general form of the swimbladder is described and illustrated for representatives of 50 out of the 82 genera of clupeoid fishes (families Chirocentridae, Clupeidae, Pristigasteridae and Engraulididae of the suborder Clupeoidei), based mainly on preserved specimens. There is a remarkable diversity of shape, volume and silvering, as well as many curious specializations. The point of origin of the pneumatic duct from the gut, the presence or absence of an anal duct, and the length and diameter of the pre-coelomic ducts are noted, with attempts to explain their functional significance in terms of feeding and vertical migration. Specializations such as dorsal or lateral pockets, post-coelomic diverticula and internal muscular processes may be connected with sound production. The taxonomic implications of this diversity of swimbladder form are explored but, while some intra-and intergeneric relationships arc either confirmed or challenged, the swimbladder gives little help at suprageneric levels.