Elopiformes

(Ladyfish and tarpon)

Class Actinopterygii

Order Elopiformes

Number of families 2

Evolution and systematics

Tarpon, along with bonefish and ladyfish, are primitive fishes, and while tarpon and ladyfish are considered to be more closely related to each other than to any other elopomorph group, their distinct lineages extend more than 100 million years back in the fossil record. The structure of the skull, fin placement, and large thick scales are characteristic of ancient fishes.

Tarpon and ladyfish are united by the common possession of a leptocephalus larvae and a variety of primitive features. The leptocephalus larvae is shared with a diverse group of other elopomorph fishes including the eels; however, the leptocephalus larvae of tarpon and ladyfish are the smallest of all leptocephali and possess a forked tail. Leptocephali of some albuliformes also have a forked tail.

The order Elopiformes contains two families: the Elopidae and the Megalopidae. The family Megalopidae contains the single genus Megalops. Two species of tarpon exist worldwide. The Atlantic tarpon occurs in the eastern and western Atlantic, and the oxeye tarpon occurs in the Indian and Pacific oceans. Morphologically the two species are quite similar; however, the Atlantic tarpon reaches a much larger size and can exceed 220 lb (100 kg) and a length of over 6.6 ft (2 m). The oxeye tarpon is smaller and seldom exceeds 3.3 ft (1 m).

The family Elopidae contains the single genus Elops, which occurs worldwide. As many as six morphologically similar species of Elops are thought to exist. The genus is in need of revision, and the total number of species is unclear.

Physical characteristics

These are silver, elongate herring-like fishes with large upturned mouths, large eyes, and deeply forked tails. An important structural character is the presence of a long, bony gular plate between the branches of the lower jaw, a feature that the ladyfish shares with the tarpon but not with herring.

Distribution

The Megalopidae and Elopidae occur worldwide in tropical and subtropical seas.

Habitat

Tarpon and ladyfish are coastal in habitat and often occur in estuarine waters. Both tarpon and ladyfish are quite tolerant of low salinities. Tarpon commonly enter freshwater and often travel far up freshwater rivers and enter lakes far from sea.

Behavior

Tarpon and ladyfish are pelagic predators that feed principally on mid-water prey. Both have small sandpaper-like teeth, and their prey is swallowed whole. They often occur in large schools in shallow coastal and inshore waters.

Feeding ecology and diet

Small tarpon feed predominantly on cyclopoid copepods, fishes, caridean shrimp, and mosquito larvae. No detailed studies have examined the feeding habits of large tarpon, but anecdotal information suggests that a wide variety of fishes are consumed. Ladyfish feed principally in midwater on pelagic prey. Feeding is mainly on fish, but decapod crustaceans also are consumed.

Ladyfish are probably preyed upon by a wide variety of inshore predators including sharks, porpoises, snook, and tarpon. They are occasionally used as bait by recreational anglers for tarpon and other species. Juvenile tarpon are also likely preyed upon by a variety of species such as gar, snook, and larger tarpon. Because juvenile tarpon are most often found in poorly oxygenated waters, they are probably vulnerable to a more limited suite of predators than ladyfish. Large tarpon are preyed upon only by large coastal sharks including bull sharks and hammerheads.

Reproductive biology

Both tarpon and ladyfish spawn offshore in high salinity oceanic waters. Precise spawning areas are unknown, and fertilized eggs are undescribed. Tarpon and ladyfish are broadcast spawners that produce large numbers of buoyant eggs that float in the surface waters of the ocean. The eggs hatch into the distinctive leptocephalus larvae characterized by an elongate, laterally compressed body consisting principally of an acellular mucinous material, large well-developed eyes, and large fang-like teeth. Larvae of tarpon and ladyfish reach a length of from 1.0 to 2.0 in (25–50 mm) before metamorphosis. Metamorphosis occurs as the larvae enter coastal waters and pass through inlets into the inshore waters where juveniles are found. Recruitment of tarpon through inlets appears to be pulsed and related to storm events.

Conservation status

Tarpon and ladyfish are abundant, and there is no evidence that stocks of these species have been depleted by overfishing. It is unknown to what extent habitat loss has affected stocks.

Significance to humans

Tarpon support important recreational fisheries in Florida and the Caribbean. Ladyfish are a food fish of minor importance in some areas.

Species accounts

List of Species

Atlantic tarpon

Megalops atlanticus

taxonomy

Megalops atlanticus Valenciennes, 1847, Guadeloupe, Santo Domingo, Martinique, and Puerto Rico.

Anglers have long believed that the tarpon in some areas were different and larger than in other areas, but there is no genetic basis for this belief. While some areas may attract larger fish, these fish are not different genetically from those found elsewhere in the western Atlantic, and they all appear to interbreed freely. However, the tarpon of the eastern Atlantic do appear to be genetically distinct from their western Atlantic cousins. These populations have probably been isolated by the vast expanse of the Atlantic Ocean, and there is little or no interbreeding with western Atlantic tarpon. In is not known if the exceptionally large sizes attained by African tarpon have a genetic or environmental basis, but the isolation of the two stocks indicates that the differences could be genetically based.

other common names

None known.

physical characteristics

Elongate and highly compressed body. Eye large. Mouth oblique with a prominently projecting lower jaw. Large, thick, prominent scales. Teeth small and feel like sandpaper when touched. All fins are soft rayed. A single dorsal fin is located behind the pelvic fins but entirely before the anal fin; the dorsal fin has a distinctive and greatly prolonged final ray. The final ray of the anal fin is also somewhat elongate, but much less so than that of the dorsal fin. Deeply forked caudal fin. Tarpon are bright silvery all over, and the back is darker than the sides or belly.

distribution

Both sides of the tropical and subtropical Atlantic Ocean. In the western Atlantic, tarpon regularly occur from the eastern shore of Virginia to central Brazil and throughout the Caribbean Sea and Gulf of Mexico, as well as off Central and South America. At least seven records exist from as far north as Nova Scotia, where a few large tarpon have been captured between August and October. Tarpon also are present in the eastern Atlantic off the coast of tropical Africa and are occasionally found as far north as Portugal and France. There is a single record of a tarpon from Ireland. African tarpon are known to reach exceptionally large sizes, and many recent world records have come from this area, including some unconfirmed reports of 330.7-lb (150-kg) fish. Tarpon are sexually dimorphic, and females reach much larger sizes than males.

habitat

Young-of-the-year tarpon occur in small stagnant pools and sloughs of varying salinity and have been reported from North Carolina, Georgia, Florida, Texas, Caribbean islands, Costa Rica, and Venezuela. In tropical areas, juvenile tarpon typically occur in mangrove habitats, often in water with low dissolved oxygen levels. Tarpon occur in salinities ranging from freshwater to more than 45 parts per thousand and are capable of surviving temperatures of at least 105°F (65.6°C), but they suffer mortalities at temperatures of 50–55°F (10–12.8°C). Large numbers of tarpon die during severe cold fronts off Florida.

behavior

Anglers often detect the presence of schools of tarpon by observing individuals "rolling" at the surface. The tarpon's habit of rising to the surface and breathing air is unusual among marine species, although this practice is common among tropical freshwater swamp-dwelling fishes. Breathing air is accomplished by way of a highly vascularized swimbladder that functions as an air-breathing organ. The swimbladder is an elongate, balloon-like sac located above the viscera and just below the backbone. In most fish species, the swimbladder acts as a buoyancy control mechanism. The fish can adjust the volume of air in the bladder and remain neutrally buoyant. In tarpon, this swimbladder is connected to the gut by a duct enabling the tarpon to gulp air and ventilate the swimbladder. Young tarpon, when held in experimental chambers from which all of the dissolved oxygen has been removed, are able to meet their oxygen needs by breathing air. This adaptation allows tarpon to survive in water with low dissolved oxygen concentrations such as commonly encountered by juveniles in hot, stagnant mangrove marshes. Experimental work also suggests that tarpon are facultative air-breathers, and in well-oxygenated waters are able to meet their oxygen requirements without breathing air. Young tarpon can survive in well-oxygenated water when deprived of the opportunity to reach the surface and breathe air. However, after several unsuccessful attempts to reach the surface they have emptied their swimbladders and become negatively buoyant until allowed access to the surface again.

feeding ecology and diet

Small tarpon (0.6–3.0 in [16–75 mm]) feed predominantly on cyclopoid copepods, fishes, caridean shrimp, and mosquito larvae. No detailed studies have examined the feeding habits of large tarpon, but anecdotal information suggests that a wide variety of fishes are consumed, including mullet (Mugil spp.), pinfish (Lagodon rhomboides), ariid catfishes, and clupeids, as well as crabs and shrimp.

reproductive biology

Female tarpon are larger than males regardless of capture location, and average fish size varies geographically. Sexually mature Florida females average about 110 lb (50 kg) and can exceed 220 lb (100 kg). In contrast, sexually mature Florida males average only 66 lb (30 kg), and they rarely exceed 110 lb (50 kg).

Tarpon from Costa Rican waters are year-round spawners, unlike tarpon from other areas. Inactive or resting ovaries are rare in Costa Rica females, suggesting that females spawn repeatedly throughout the year and have no extended period of inactivity. In Florida, tarpon spawning is seasonal and peaks between May and July. By August, most females are finished spawning. In the Southern Hemisphere, off the northeast coast of Brazil, researchers have reported that tarpon spawn from October to January—during the Southern Hemisphere's spring and summer.

Ripe tarpon ovaries are large and can contain up to 20 million maturing oocytes and many more small resting oocytes. "Oocyte" is the proper name of a developing egg that has not ovulated and is not yet ready to be spawned. Although hundreds of mature female tarpon have been examined during the spawning season, none have been caught in the act of spawning. This is probably because spawning occurs in areas not typically fished. Even though the number of eggs released by a female in a single spawning event is unknown, the numbers of developing oocytes in the ovary suggests that their reproductive output is immense.

Tarpon are relatively long lived and can live more than 50 years. By age one, tarpon are about 1.5 ft (450 mm) long and are common in rivers and the upper reaches of estuaries, where they remain until reaching sexual maturity. In Florida, sexual maturity is reached at an age of about 10 years. After attaining sexual maturity, tarpon become more coastal in habitat and are most numerous around inlets and off beaches. Large tarpon targeted by anglers in Florida are typically from 15 to 35 years old.

conservation status

Florida's fishery is intensely regulated, and anglers must purchase a $50 permit before harvesting a fish. Since the establishment of the permit system in 1989, the harvest of tarpon in Florida has declined to fewer than 100 fish per year, and the fishery is now mostly catch-and-release. Encouraging catch-and-release fishing for tarpon has been an effective management strategy, because the vast majority of released fish survive to be caught again. The sale of tarpon in Florida is prohibited, but in most of their range tarpon have never been considered a desirable food fish.

significance to humans

In Central America and South Florida, tarpon are the basis of economically important recreational fisheries. Tarpon occur in a variety of habitats ranging from freshwater lakes and rivers to offshore marine waters, but large tarpon targeted by Florida's fishery are most abundant in estuarine and coastal waters. In Florida, the fishery is seasonal; most tarpon are caught between May and July, although some fish are caught in all months. Tarpon are known for their spectacular leaps from the water when hooked and for their willingness to enter shallow water and eat artificial baits. Probably more than any other species, tarpon offer anglers in small boats an opportunity to pursue a large gamefish. Tarpon are pursued by a large for-hire charter boat fleet in Florida.

Ladyfish

Elops saurus

taxonomy

Elops saurus Linnaeus, 1766, "Carolina." The taxonomic status of Elops saurus is unclear, and this name may be applied to more than one species.

other common names

None known.

distribution

Abundant from North Carolina south through the Gulf of Mexico and into the Caribbean.

physical characteristics

Ladyfish have a single, soft-rayed dorsal fin that originates about midway along the back. The pelvic fins are located midway between the tip of the snout and the fork of the deeply forked caudal fin. Scales are small and thin. Ladyfish are silvery all over; the back is bluish, and the lower parts of the sides and the belly are yellowish.

habitat

Common in estuaries and coastal waters of tropical and subtropical latitudes. Often occur in large schools. Tolerant of a wide range of salinities but seldom occur in freshwater.

behavior

Little is known other than general descriptions of feeding habits and reproductive migrations. Ladyfish can be extremely abundant and most often occur in large schools. They are voracious predators.

feeding ecology and diet

Ladyfish feed principally in midwater on pelagic prey. Feeding is mainly on fish, but decapod crustaceans also are consumed.

reproductive biology

Spawning appears to occur offshore. Larvae are common in the Gulf of Mexico and off the southern United States, where they have been reported as far north as Virginia. Fertilized eggs are undescribed. Spawning may occur throughout the year but probably peaks during fall in Florida and in the Gulf of Mexico.

conservation status

Not threatened.

significance to humans

Ladyfish are often caught by recreational anglers but are seldom a targeted species. Ladyfish are voracious predators and will attack a variety of lures and baits. The species is fished commercially in Florida and sold both for human consumption and as bait to recreational anglers.

Resources

Books

Hildebrand, S. F. "Family Elopidae." In Fishes of the Western North Atlantic, edited by H. B. Bigelow. New Haven, CT: Sears Foundation for Marine Research, 1963.

Periodicals

Andrews, A., E. Burton, K. Coale, G. Cailliet, and R. E. Crabtree. "Radiometric Age Validation of Atlantic Tarpon, Megalops atlanticus." Fishery Bulletin 99 (2001): 389–398.

Crabtree, R. E., E. C. Cyr, R. E. Bishop, L. M. Falkenstein, and J. M. Dean. "Age and Growth of Larval Tarpon, Megalops atlanticus, in the Eastern Gulf of Mexico With Notes on Relative Abundance and Probable Spawning Areas." Environmental Biology of Fishes 35 (1992): 361–370.

Crabtree, R. E., E. C. Cyr, D. Chacon, W. O. McLarney, and J. M. Dean. "Reproduction of Tarpon, Megalops atlanticus, from Florida and Costa Rican Waters and Notes on Their Age and Growth." Bulletin of Marine Science 61 (1997): 271–285.

Geiger, S. P., J. J. Torres, and R. E. Crabtree. "Air-breathing and Gill Ventilation Frequencies in Juvenile Tarpon, Megalops atlanticus: Responses to Changes in Dissolved Oxygen, Temperature, Hydrogen Sulfide, and pH." Environmental Biology of Fishes 59 (2000): 181–190.

Zale, A. V. and S. G. Merrifield "Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (South Florida)—Ladyfish and Tarpon." U.S. Fish and Wildlife Service Biological Report 82 (1989).

Roy Eugene Crabtree, PhD