Dogfish: Sharks of the family Squalidae, also called dogfish sharks. They comprise at least eight genera and 44 species. Their LIVER is valued for its oil and its flesh is often made into fertilizer.Squalus acanthias: A species of shark in the family SQUALIDAE, used for its oil (SQUALENE) and as fish meal. It also figures heavily in biological research, especially with reference to its RECTAL GLAND in studies of WATER-ELECTROLYTE BALANCE.Sharks: A group of elongate elasmobranchs. Sharks are mostly marine fish, with certain species large and voracious.Salt Gland: A compound tubular gland, located around the eyes and nasal passages in marine animals and birds, the physiology of which figures in water-electrolyte balance. The Pekin duck serves as a common research animal in salt gland studies. A rectal gland or rectal salt gland in the dogfish shark is attached at the junction of the intestine and cloaca and aids the kidneys in removing excess salts from the blood. (Storer, Usinger, Stebbins & Nybakken: General Zoology, 6th ed, p658)Gills: Paired respiratory organs of fishes and some amphibians that are analogous to lungs. They are richly supplied with blood vessels by which oxygen and carbon dioxide are exchanged directly with the environment.Interrenal Gland: Structures in fishes homologous to the cortical tissue of the mammalian adrenal gland; they are in close proximity to or imbedded in the kidney.