Gobiidae or gobies is a family of bony fish in the order Gobiiformes, one of the largest fish families comprising more than 2,000 species in more than 200 genera. Most of gobiid fish are relatively small, typically less than 10 cm (3.9 in) in length, and the family includes some of the smallest vertebrates in the world, such as Trimmatom nanus and Pandaka pygmaea, Trimmatom nanus are under 1 cm long when fully grown, then Pandaka pygmaea standard length are 9 mm (0.35 in), maximum known standard length are 11 mm (0.43 in). Some large gobies can reach over 30 cm (0.98 ft) in length, but that is exceptional. Generally, they are benthic or bottom-dwellers. Although few are important as food fish for humans, they are of great significance as prey species for other commercially important fish such as cod, haddock, sea bass and flatfish. Several gobiids are also of interest as aquarium fish, such as the dartfish of the genus Ptereleotris. Phylogenetic relationships of gobiids have been studied using molecular data.

Sequential hermaphroditism is one of the two types of hermaphroditism, the other type being simultaneous hermaphroditism. It occurs when the organism's sex changes at some point in its life. A sequential hermaphrodite produces eggs and sperm at different stages in life. Sequential hermaphroditism occurs in many fish, gastropods, and plants. Species that can undergo these changes do so as a normal event within their reproductive cycle, usually cued by either social structure or the achievement of a certain age or size. In some species of fish, sequential hermaphroditism is much more common than simultaneous hermaphroditism.