State of the Art of Multiple Vitellogenin System in Fishes

In most oviparous vertebrates, including fish, the establishment of the yolk and eggshell proteins is essential for oocyte formation (zona radiata proteins). Unlike vitellogenesis, which involves a series of processes in which the liver produces vitellogenin, which is then secreted into the circulation where it is confined into the developing oocytes before being broken by a proteolytic action to make yolk proteins and ultimately deposited in the oocytes. Many investigations have been made on various fish species to understand more about vitellogenin and yolk protein levels, their makeup, and their roles in fish reproduction. Generally, it has a linear chain with domains such as terminal amino acid-lipovitellin, phosvitin, β-carotene component-c-terminal carboxyl group. In fishes, there are two types of vitellogenin: complete (VgA and B) and incomplete (Vg C). There are numerous claims that the meroblastic or holoblastic cleavage pattern, the features of the egg, and the placental or nonplacental method of reproduction ultimately depend on the existence or lack of the vitellogenin (Vtg) gene family in vertebrates (pelagic or benthic). Using advanced techniques multiple vitellogenins was determined in fishes.