the first fish appeared in late cambrian (answer with era period).
the first fish appeared in late cambrian (answer with era period).
when did the first fish appear (answer with era period)?
late cambrian
the evolution of fish began about 530 million years ago during the cambrian explosion. it was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. the first fish lineages belong to the agnatha, or jawless fish. early examples include "haikouichthys". during the late cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. lampreys belong to the cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
evolution of fish
as a simultaneous hermaphrodite, "h. nigricans" has an unusual reproductive strategy known as egg trading. the fish is usually solitary, but at breeding time two fish come together at night. courtship is initiated by one fish which temporarily takes a female role. the other fish acts as the male and fertilises a batch of eggs produced by the first fish. the following night their roles are reversed, and the second fish lays eggs and the first fish fertilises them. the two fish continue alternating roles in this way over the course of several nights. the pair usually stay together for the series of transfers, but sometimes each finds a different partner.
hypoplectrus nigricans