Editing Metamorphosis (section)

=== Fish ===
Some fish, both [[Osteichthyes|bony fish (Osteichthyes)]] and [[Agnatha|jawless fish (Agnatha)]], undergo metamorphosis. Fish metamorphosis is typically under strong control by the thyroid hormone.<ref name="Laudet" />

Examples among the non-bony fish include the [[lamprey]]. Among the bony fish, mechanisms are varied.

The [[salmon]] is [[diadromous]], meaning that it changes from a [[freshwater]] to a [[Seawater|saltwater]] lifestyle.

Many species of [[flatfish]] begin their life [[bilaterally symmetrical]], with an eye on either side of the body; but one eye moves to join the other side of the fish – which becomes the upper side – in the adult form.

The [[European eel]] has a number of metamorphoses, from the larval stage to the [[leptocephalus]] stage, then a quick metamorphosis to glass eel at the edge of the continental shelf (eight days for the [[Japanese eel]]), two months at the border of fresh and salt water where the glass eel undergoes a quick metamorphosis into elver, then a long stage of growth followed by a more gradual metamorphosis to the migrating phase. In the pre-adult [[Fresh water|freshwater]] stage, the eel also has [[phenotypic plasticity]] because fish-eating eels develop very wide mandibles, making the head look blunt. [[Leptocephalus|Leptocephali]] are common, occurring in all [[Elopomorpha]] ([[tarpon]]- and [[eel]]-like fish).

Most other bony fish undergo metamorphosis initially from [[fish egg|egg]] to immotile larvae known as ''sac fry'' ([[fry (biology)|fry]] with a [[yolk sac]]), then to motile larvae (often known as [[fingerling (fish)|fingerling]]s due to them roughly reaching the length of a [[human finger]]) that have to [[foraging|forage]] for themselves after the yolk sac resorbs, and then to the juvenile stage where the fish progressively start to resemble [[adult]] morphology and behaviors until finally reaching [[sexual maturity]].<ref>Mader, Sylvia, ''Biology'' 9th ed. Ch. 31</ref><ref>Peter B. Moyle and Joseph J. Cech Jr, ''Fishes: an introduction to ichthyology'' 5th ed. 9.3: "Development" pp 148ff</ref>