Tarpon
Tarpons are fish of the genus Megalops. They are the only members of the family Megalopidae. Of the two species, one (M. atlanticus) is native to the Atlantic, and the other (M. cyprinoides) to the Indo-Pacific Oceans.
The two species of tarpons are M. atlanticus (Atlantic tarpon) and M. cyprinoides (Indo-Pacific tarpon). M. atlanticus is found on the western Atlantic coast from Virginia to Brazil, throughout the Caribbean and the coast of the Gulf of Mexico. Tarpons are also found along the eastern Atlantic coast from Senegal to South Angola.[4] M. cyprinoides is found along the eastern African coast, throughout Southeast Asia, Japan, Tahiti, and Australia. Both species are found in both marine and freshwater habitats, usually ascending rivers to access freshwater marshes.[5] They are able to survive in brackish water, waters of varying pH, and habitats with low dissolved O
2 content due to their swim bladders, which they use primarily to breathe. They are also able to rise to the surface and take gulps of air, which gives them a short burst of energy. The habitats of tarpons vary greatly with their developmental stages. Stage-one larvae are usually found in clear, warm, oceanic waters, relatively close to the surface. Stage-two and -three larvae are found in salt marshes, tidal pools, creeks, and rivers. Their habitats are characteristically warm, shallow, dark bodies of water with sandy mud bottoms. Tarpons commonly ascend rivers into fresh water. As they progress from the juvenile stage to adulthood, they move back to the open waters of the ocean, though many remain in freshwater habitats.[6][7]
Fossils of this genus go back to the Cretaceous during the Albian stage 113.0 million years ago (Mya).[8][9]
Tarpons grow to about 4–8 ft (1.2–2.4 m) long and weigh 60–280 lb (27–127 kg). They have dorsal and anal soft rays and bluish or greenish backs. Tarpons possess shiny, silvery scales that cover most of their bodies, excluding the head. They have large eyes with adipose eyelids and broad mouths with prominent lower jaws that jut out farther than the rest of the face.[4][5][6]
Tarpons breed offshore in warm, isolated areas. Females have high fecundity and can lay up to 12 million eggs at once. They reach sexual maturity once they are about 75–125 cm (30–50 in) in length. Spawning usually occurs in late spring to early summer.[6] Their three distinct levels of development usually occur in varying habitats. Stage one, or the leptocephalus stage, is completed after 20–30 days. It takes place in clear, warm oceanic waters, usually within 10–20 m of the surface. The leptocephalus shrinks as it develops into a larva; the most shrunken larva, stage two, develops by day 70. This is due to a negative growth phase followed by a sluggish growth phase. By day 70, the juvenile growth phase (stage three) begins and the fish begins to grow rapidly until reaching sexual maturity.[4][11]
Stage-one developing tarpons do not forage for food, but instead absorb nutrients from seawater using integumentary absorption. Stage-two and -three juveniles feed primarily on zooplankton, but also on insects and small fish. As they progress in juvenile development, especially those developing in freshwater environments, their consumption of insects, fish, crabs, and grass shrimp increases. Adults are strictly carnivorous and feed on midwater prey; they hunt nocturnally and swallow their food whole.[6][7]
