Pronephric anatomy

Compared to the mature mammalian kidney with its million nephrons, the teleost pronephros is a relatively simple organ.

The teleost pronephros is composed of a pair of nephrons with two glomeruli fused at the midline, pronephric tubules connecting directly to the glomeruli via a neck segment, and paired bilateral pronephric ducts which convey the altered blood filtrate outside the animal. This diagram shows the zebrafish pronephros at about 3 days post-fertilization, after hatching and at a stage when the pronephros must function for larval osmoregulation.

The teleost pronephros shares many essential features with the amphibian pronephros including its derivation from mesoderm associated with the coelom and the derivation of the glomerular blood supply from the medial dorsal aorta. However, unlike the pronephros of amphibians which have an external glomus and tubules with nephrostomes open to the coelom, the mature teleost pronephros has no connection to the body cavity and instead functions as a closed system.