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The development of functional digestive and metabolic organs in turbot,Scophthalmus maximus
Authors:H Segner  V Storch  M Reinecke  W Kloas  W Hanke
Institution:(1) Department of Zoology, University of Karlsruhe, Post Box 6980, D-76128 Karlsruhe, Germany;(2) Department of Zoology, University of Heidelberg, Im Neuenheimer Feld 230, D-69120 Heidelberg, Germany;(3) Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Winterthurer Str. 190, CH-8057 Zürich, Switzerland;(4) Present address: Laboratory of Cell Toxicology, Department of Environmental Chemistry & Ecotoxicology, Centre for Environmental Research, Permoser Str. 15, D-04318 Leipzig, Germany
Abstract:The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, Scophthalmus maximus, provides an overview on the ontogeny of structure and functions involved in digestion, absorption and metabolism of nutrients. At start of exogenous feeding the intestine of larval turbot is anatomically differentiated, with enterocytes displaying an adult-type ultrastructure and being able to process lipids. At the microvillous border of the enterocytes, enzymes of contact digestion such as aminopeptidase are found. The ultrastructure of the exocrine pancreatic cells is fully differentiated from hatching onwards. Likewise, substantial activities of trypsin-type proteases are present. A stomach anlage exists in first-feeding larvae; however, the stomach becomes functional (appearance of gastric glands and pepsin secretion) only during metamorphosis. Liver parenchymal cells already display a functional ultrastructure during the endotrophic phase; with onset of exogenous feeding they develop pronounced diet-related changes of their energy stores. Larval respiration is not executed by the gills since respiratory surface of these structures develops only towards metamorphosis. The energy generation of larval muscle tissue depends on aerobic metabolism, whereas glycolytic activities start to increase at metamorphosis. In conclusion, two important patterns can be recognized in the development of turbot larvae: (1) The structure/function is differentiated at hatching or at the onset of exogenous feeding (afterwards it experiences mainly quantitative but not qualitative growth, i.e., intestine, exocrine pancreas, liver); or (2) the structure/function is absent in larvae and develops only during metamorphosis (i.e., gills, glycolytic muscle metabolism, stomach).
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