Development and aging of the liver and pancreas in the domestic carp, Cyprinus carpio: From embryogenesis to 15-year-old fish

The cytology of development and aging of the liver and pancreas in domestic carp was studied in a large sample of EM and LM sections from larvae juven iles 1-10 year old adults and 15 year old experimentally stunted fish weigh ing 20 g and of 110-120 mm TL. The primordium of the two glands appears in embryos 3-4 days after fertilization as buds from the gut wall. Formation o f the hepatic tubules is first seen in larvae 10 days after fertilization. Two types of hepatocytes are discernable: one with a pale cytoplasm and the other with a dense opaque cytoplasm; both extend microvilli into the sinus oidal space of Disse and bear intracellular bile canaliculi. With maturatio n and branching of the hepatic tubules a complicated hepatic muralium is fo rmed. The pancreatic cells develop in 5-6 mm TL embryos primarily along the blood capillaries and in 10-11 day old larvae exocrine A and B cells are s een prominent by their zymogen granules and spires and stacks of rough endo plasmic reticulum. Ripening of the Islets of Langerhans begin in larvae of 10 mm TL. By 16 mm TL two types of endocrine cells are visible. With aging three processes are recognizable in the liver: (1) increased branching of t he blood net displaces the hepatic units and complicates the structure of t he liver parenchyma; (2) a gradual increase in lipid vacuoles and debris de position in secretory cells takes place; and (3) the number of melano-macro phage cells and melano-macrophage centers gradually increases. In 15-year-o ld experimentally stunted fish (110-120 mm TL) the liver and pancreas resem ble those of juvenile fish appearing much healthier than those of 8-10 year old large carp from commercial ponds. These findings provide evidence that aging is not a simple time-dependent mechanism but is also strongly modula ted by environmental factors.