ABSTRACT
Teleost kidneys regulate water balance and ion concentration and are therefore part of the osmoregulatory and excretory system; however, most of the protein metabolism is excreted by the gills. In addition, kidneys comprise hematopoietic, phagocytotic, endocrine elements, and lymphoid tissue. The structures which have osmoregulatory and excretory function are the nephrons. These functional elements of the kidney consist of the renal corpuscule (Malphigian body) and a renal tubule (urinary tubule). The Malphigian body is composed of the glomerulus and a surrounding capsule (Bowman’s capsule). The urinary tubules are connected to two collecting ducts (also called Wolffian ducts) which join together in the caudal part of the kidney and become the ureter. The anatomy of the nephrons is different in stenohaline marine teleosts which are characterized by hypo-osmoregulation and freshwater teleosts which perform hyper-osmoregulation. In marine teleosts, the nephron is comprised of the renal corpuscule and the renal tubule. The renal tubule contains an early and a late proximal tubule. In freshwater teleosts, the nephrons consist of the Malphigian body and tubules comprised of a proximal tubule, a distal tubule and a collecting tubule. Urine flow and composition in freshwater teleosts differs considerably from that of marine fishes.
