Context: A fish is any member of a group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification., The European eel ("Anguilla anguilla") is a species of eel, a snake-like, catadromous fish. They can reach a length of in exceptional cases, but are normally around , and rarely reach more than . While captive specimens have lived over 85 years in captivity, the species' lifespan in the wild has not been determined. 
Life history.
Much of the European eels life history was a mystery for centuries, as fishermen never caught anything they could identify as a young eel. Unlike many other migrating fish, eels begin their life cycle in the ocean and spend most of their lives in fresh inland water, or brackish coastal water, returning to the ocean to spawn and then die. In the early 1900s, Danish researcher Johannes Schmidt identified the Sargasso Sea as the most likely spawning grounds for European eels. The larvae (leptocephali) drift towards Europe in a 300-day migration. When approaching the European coast, the larvae metamorphose into a transparent larval stage called "glass eel", enter estuaries, and many start migrating upstream. After entering their continental habitat, the glass eels metamorphose into elvers, miniature versions of the adult eels. As the eel grows, it becomes known as a "yellow eel" due to the brownish-yellow color of their sides and belly. After 520 years in fresh or brackish water, the eels become sexually mature, their eyes grow larger, their flanks become silver, and their bellies white in color. In this stage, the eels are known as "silver eels", and they begin their migration back to the Sargasso Sea to spawn., Synbranchiformes , often called swamp eels , is an order of ray - finned fishes that are eel - like but have spiny rays , indicating that they belong to the superorder Acanthopterygii ., An eel is any fish belonging to the order Anguilliformes, which consists of four suborders, 20 families, 111 genera and about 800 species. Most eels are predators. The term "eel" (originally referring to the European eel) is also used for some other similarly shaped fish, such as electric eels and spiny eels, but these are not members of the Anguilliformes order., Actinopterygii , or the ray-finned fishes, constitute a class or subclass of the bony fishes., The name spiny eel is used to describe members of two different families of fish: the freshwater Mastacembelidae of Asia and Africa, and the marine (and generally deep sea) Notacanthidae. Both are so-named because of their eel-like shape and sturdy fin spines. These two families are not related and that the Notacanthiformes belong to the Superorder Elopimorpha, of which members are characterized by having a leptocephalus larvae. The freshwater Mastacembelids do not share this characteristic and are popular specimens in the aquarium trade. 
Mastacembelid Spiny eels originate from three places. The Middle East, Southeast Asia and Africa. , Acanthopterygii (meaning "spiny finned one") is a superorder of bony fishes in the class Actinopterygii. Members of this superorder are sometimes called ray-finned fishes for the characteristic sharp, bony rays in their fins; however this name is often given to the class Actinopterygii as a whole., Subject: synbranchiformes, Relation: parent_taxon, Options: (A) acanthopterygii (B) actinopterygii (C) anguilla (D) anguilliformes (E) mastacembelidae (F) notacanthiformes (G) olfactores (H) snake
Output: actinopterygii