Tarpons are large fish of the genus Megalops. There are two species of Megalops, one native to the Atlantic, and the other to the Indo-Pacific

Indo-Pacific

The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...

 oceans.
They are the only members of the family Megalopidae.

Species and habitats

There are two species of tarpons, the Megalops atlanticus (the Tarpon) and the Megalops cyprinoides (the Indo-Pacific tarpon). Megalops atlanticus is found on the western Atlantic coast

Atlantic Coast

The Atlantic Coast is any coast fronting the Atlantic Ocean. The term differentiates the coasts of countries or continents with coastlines on more than one body of water, such as North America, South America, Africa and Europe.-See also:*Indian Ocean...

 from Virginia

Virginia

The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...

 to Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, throughout the coast of the Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

, throughout the Caribbean

Caribbean

The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...

. Tarpons are also found along the eastern Atlantic coast from Senegal

Senegal

Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...

 to South Angola

Angola

Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...

. Megalops cyprinoides is found along the eastern African coast, throughout southeast Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, Tahiti

Tahiti

Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...

, and Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. Both species are found in both salt

Salt water

Salt water or saltwater may refer to:* Saline water, water containing salts* Brine, with salt* Brackish water, water that is saltier than fresh water, but not as salty as seawater* Seawater, water from oceans or seas...

 and freshwater

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 habitats usually ascending rivers to access freshwater marshes. They are able to survive in brackish water

Brackish water

Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

, waters of varying pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

, as well as habitats with low dissolved content due to their swim bladders which they use primarily to breathe. The habitat of the tarpon varies greatly with the developmental stage they are in. 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. The habitats are characteristically warm, shallow, dark bodies of water with sandy mud bottoms. It is quite common for tarpon to ascend rivers into freshwater. 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.

Physical characteristics

Tarpons grow to about 5–8 ft. long and weigh 80-280 lbs. They have dorsal and anal soft rays and have a bluish or greenish back. Tarpons possess distinctive lateral lines and have shiny silvery scales that cover most of the body excluding the head. Tarpons have large eyes with adipose eyelids and a broad mouth with a prominent lower jaw that juts out farther than the rest of the face.

Reproduction and life cycle

Tarpons breed offshore in warm isolated areas. Females have a high fecundity and can lay up to 12 million eggs at once. They reach sexual maturity once they are about 75–125 cm in length. Spawning usually occurs in late spring to early summer.
There are three distinct levels of development that usually occur in varying habitats. The first stage is the Leptocephali stage, or stage one, which is completed after 20–30 days. It takes place in clear, warm oceanic waters usually within 10-20m of the surface. The Leptocephali shrinks as it develops into a larva with the most shrunken larva, stage two, developing 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 organism begins to rapidly grow until it reaches sexual maturity.

Diet

Stage one developing Megalops do not forage for food but instead absorb nutrients from sea water using integumentary absorption. Stage two and three juveniles feed primarily on zooplankton but also feed 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 mid-water prey; they swallow their food whole and hunt nocturnally.

Predation

The main predators of Megalops during stage one and early stage two development are other fish and some zooplankton depending on the size of the Megalops larvae. Juveniles are subject to predation by other juvenile Megalops and piscivorous birds. Adults occasionally fall prey to sharks, porpoises, alligators, and piscivorous birds. They are especially vulnerable to birds when they come to the surface for air due to the rolling manner in which they move to take in air as well as the silver scales that line the sides of the Megalops.

Swim bladder

One of the unique features of Megalops is the function of the swim bladder as a pseudo-respiratory organ. These gas structures can be used for buoyancy, as an accessory respiratory organ, or both. In Megalops, it is an unpaired air holding structure that arises dorsally from the posterior pharynx. Megalops uses the swim bladder as a respiratory organ and the respiratory surface is coated with blood capillaries with a thin epithelium overtop. This is the basis of the alveolar tissue that is found in the swim bladder and is believed to be one of the primary methods by which Megalops “breathe”. Megalops are obligate air breathers, and if they are not allowed to access the surface they will die. The exchange of gas that occurs is done at the surface through a rolling motion that is commonly associated with Megalops sightings. It is believed that this “breathing” is mediated by visual cues and that the frequency of breathing is inversely correlated to the dissolved content of the water in which they live.

Megalops and humans

Megalops are considered one of the great saltwater game fishes. They are prized not only because of their great size but also because of the fight that they put up and their spectacular leaping ability. Megalops are bony fish and their meat is not desirable so most Megalops are released after they are caught. There are numerous tournaments around the year that are focused on catching Megalops.

Geographical Distribution and Migration

Since Tarpons are not commercially valuable as a food fish, very little has been documented concerning their geographical distribution and migrations. Tarpons inhabit both sides of the Atlantic Ocean. Their range in the Eastern Atlantic has been reliably established from Senegal to the Congo. Tarpon inhabiting the western Atlantic are principally found to populate warmer coastal waters focused in the Gulf of Mexico, Florida, and the West Indies. Nonetheless, tarpon are regularly caught by anglers at Cape Hatteras and as far as Nova Scotia, Bermuda, and south to Argentina. There have been scientific studies principally “The Panama Canal as a Passageway for Fishes, with Lists and Remarks on the Fishes and Invertebrates Observed” by Samuel F. Hildebrand (1939) which indicate that schools of Tarpons have routinely migrated through the Panama Canal from the Atlantic to the Pacific and back for over 70 years. However it has not been scientifically established that they breed in the Pacific Ocean. Nevertheless anecdotal evidence by tarpon fishing guides and anglers would tend to validate this notion as over the last 60 years many small juvenile tarpon as well as mature giants have been caught and documented principally on the Pacific side of Panama at the Bayano River as well as in the Gulf of San Miguel and its tributaries but also as far as Coiba Island in the Gulf of Chiriquí plus at Piñas Bay in the Gulf of Panama. It would seem that since Tarpon tolerate wide ranges in salinity throughout their lives and will eat almost anything dead or alive, that their migrations are only limited by water temperatures. Tarpons prefer water temperatures of 72 to 82 F; below 60 degrees they become inactive, and temperatures under 40F can be lethal.

External links

• Tarpon Geographical Distribution and Migration