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Tarpons, Eels and Halosaurs

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Whitemouth moray - Gymnothorax meleagris

Whitemouth moray - Gymnothorax meleagris

Photo © Jeff Hunter / Getty Images.
Tarpons, eels and halosaurs (Elopomorpha) are a group of ray-finned fishes. Although members of the Elopomorpha are quite different in appearance as adults, their similarities are most apparent during the larval stage of their life. The fish in this group all begin their development as a long, thin transparent larva (also called a leptocephalus larva). Tarpons, eels and halosaurs remain in the larva stage for several years before maturing into their adult form.

Most Elopomorphs are predators. Tarpons are quick swimmers and capture their prey by pursuit. Eels are slower swimmers by comparison and employ ambush hunting strategies over all-out sprints. Many Elopomorphs have long, sharp teeth, well suited for grasping and holding onto prey. Some species also have thicker teeth that enable them to crush shells. Some species shy away from active hunting and rely instead on filter feeding or scavenging dead fish from the sea floor.

The breeding cycle of some Elopomorphs, especially the freshwater eels which breed at see, involves vast migrations. North American and European freshwater eels (which inhabit freshwater lakes and rivers) swim more than 4,000 miles to their breeding grounds in the Sargasso Se in the western Atlantic. This epic journey takes from 4 to 7 months to complete, during which time they do not to eat. They spawn in deep water and then die. The larvae float on ocean currents towards coastal waters where they develop for 3 years. They then migrate up freshwater rivers and mature, before starting the cycle once again.

Eels:

Eels (Anguilliformes) are one of the three main groups of Elopomorpha. Most species of eels are marine although there are a few species that spend much of their lives in freshwater (it should be noted that these freshwater species return to marine waters to breed).

Eels tend to prefer shallow water habitats, where they dig burrows in soft sediments such as sand and mud or see amongst rocks and inside crevaces. A few species of eels are deep water dwelling fish and inhabit the edges of continental shelves or deeper waters up to 4000 meters. Some eels live in communities referred to as eel pits.

Eels are notable for their long, snake-like body shape. Their spinal column consists of more than 100 vertebrae, a structure that offers them great flexibility. The dorsal and anal fins often extend over most of the body length and though it should be noted that electric eels and spiny eels are not true eels.

Of all eel species, there are four that are of particular significance for commercial fishing. These include the American eel, the European eel, the Japanese eel and the short finned eel. The European eel is critically endangered.

Tarpons and Their Relatives:

Tarpons and their relatives (Elopiformes) differ from eels in their body structure (the bear some resemblance to herrings). Unlike eels, tarpons are not elongated but instead have a more "fish-like" body shape with a broader torso Tarpons also have scales (eels lack scales) and they have distinct fins. Tarpons, as a group, also include ladyfish, skipjacks, Jack-Rashes and tenpounders as well as several extinct lineages. There are about 10 species of tarpons and their relatives.

Halosaurs:

Halosaurs (Notacanthiformes) more closely resemble eels than the tarpons and their relatives do. Halosaurs have an elongated body and tail and their fins are reduced. Unlike eels, halosaurs have a large head and are covered in small scales. Halosaurs occur only in deep ocean habitats.There are about 17 species of halosaurs alive today. Halosaurs are benthic fish (they live on or near the seafloor) amd they live in near total darkness due to the depth of their habitat.
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