ELOPIFORM

any member of the order Elopiformes, a group of fishes considered to be the most primitive of living bony fishes. Members of this order, which contains more extinct forms than living species, include the bonefish, tarpon, and ladyfish. Living elopiforms range in size from the small bonefishes, which reach only 70 centimetres (28 inches) and weigh about 6.5 kilograms (14.5 pounds), to the 2.5-metre (8-foot) Atlantic tarpon, which may tip the scales at about 150 kg. The body is typically long, although not eel-like, and the tail is large and forked. In these fishes there is an open connection to the swim bladder, allowing air to be taken in at the mouth and passed directly into the swim bladder. In tarpons the swim bladder is highly vascularized and lunglike; these fish are air breathers and will drown if they cannot surface for air. Although adult tarpons inhabit well-oxygenated waters, the juveniles develop in stagnant tidal pools where this alternative mode of respiration enhances their survival. Elopiform fishes, except for the gisu, dwell in coastal waters as adults and are able to move into brackish or freshwater areas. The Atlantic tarpon is well known for its great leaps out of the water, and both the Pacific tarpon and the ladyfish exhibit a similar rolling behaviour at the surface; these behaviours are probably related to taking in air. Tarpons and ladyfish are fast-swimming coastal predators that feed mainly on other fish. Bonefish are bottom feeders, following the tide in to root for worms and shellfish; they crush the latter with their rounded palatal teeth. The gisu is a deepwater bottom feeder and lives mainly on worms. The elopiforms are highly fecund; one large female Atlantic tarpon contained an estimated 12,000,000 eggs, about seven times as many as the proverbially prolific codfish. These eggs are shed and fertilized in shallow waters, where they drop to the bottom. They hatch into rib bonlike larvae (leptocephalus) and are carried out to sea by currents; only those that remain in inshore waters undergo metamorphosis. Following metamorphosis the juveniles, or postlarvae, migrate into brackish pools or creeks, where they eat small crustaceans and larval insects; they return to the sea as young adults. Gisu larvae, however, undergo all postlarval stages in the deepwater environment that they share with the adults. any member of the order Elopiformes, a group of fishes considered to be the most primitive of bony fishes. The order contains about 12 species of marine and brackish water fishes, the best known of which are bonefish, tarpons, and ladyfishes. Most taxonomists recognize two living suborders of elopiforms: Elopoidei, which consists of two living families; and Albuloidei, which contains one living and one extinct family. A few elopiforms are prized gamefishes, but only the Pacific tarpon (or oxeye) is of economic importance as food, supporting a major fishery in Southeast Asia. The terms ladyfish and bonefish have both been used for Elops saurus and Albula vulpes. In this article the name ladyfish is applied only to Elops and bonefish only to Albula. The tarpons and ladyfishes are fast-swimming predators with adult lengths of up to 2.5 metres (approximately eight feet) in tarpons and about one metre (three feet, three inches) in ladyfishes. The bonefish and Japanese gisu are specialized bottom feeders. All except the gisu are coastal fishes of warm oceans, most common in latitudes from 20 N to 20 S. Elopiforms are of interest to the ichthyologist as the most primitive living teleost fishes, standing in much the same relation to the higher bony fishes as do the egg-laying mammals (monotremes) to other mammals. As is usual with primitive groups, the elopiforms have an extensive fossil record, with many more fossil than recent species. Additional reading S.F. Hildebrand, Family Elopidae and Family Albulidae, in H.B. Bigelow et al., Fishes of the Western North Atlantic, vol. 3, pp. 111147 (1963), full discussions of the structure, biology, and classification of ladyfishes, tarpons, and bonefishes; R.A. Wade, The Biology of the Tarpon, Megalops atlanticus, and the Ox-eye, Megalops cyprinoides, with Emphasis on Larval Development, Bull. Mar. Sci. Gulf Caribb., 12:545622 (1962), a detailed account of the biology of the Pacific tarpon, or oxeye, and the Atlantic tarpon; P.H. Greenwood, Skull and Swimbladder Connections in Fishes of the Family Megalopidae, Bull. Br. Mus. (Nat. Hist.), Zool., 19:119135 (1970), details of the specialized respiratory system of the tarpons; P.L. Forey, A Revision of the Elopiform Fishes, Fossil and Recent, Bull. Br. Mus. (Nat. Hist.), Geol., suppl. 10 (1973), a full account of the structure and evolution of elopiforms.