Histochemical characterization and connective fiber distribution of the cardiac outflow tract of pirarucu, Arapaima gigas (Schinz, 1822) (Osteoglossiformes, Arapaimidae)

  • Mario Vitor Buzete GardinalEmail author
  • Thalles Fernando Rocha Ruiz
  • Diego Dias dos Santos
  • Mateus Rossetto Vidal
  • Sandro Estevan Moron
  • Luiz Roberto Falleiros Junior
  • Sebastião Roberto Taboga
  • Irene Bastos Franceschini Vicentini
  • Carlos Alberto Vicentini
Original Paper


The cardiac outflow tract (OFT) in teleosts is composed of a proximal short conus arteriosus and a distal well-developed bulbus arteriosus located between the ventricle and ventral aorta. The role of these anatomical components includes structural connections, prevention of blood backflow and blood pressure control, which are related to their histological and histochemical compositions. A previous study in the heart of the Amazonian species Arapaima gigas reported an unusual OFT arrangement among teleosts that has been found only in members of Osteoglossiformes so far. Thus, considering the wide structural variability of the teleostean OFT, the present study focuses on identifying glycosaminoglycans types and describing the distribution of collagen, elastic and reticular fibers in the conus arteriosus, conal valves, and bulbus arteriosus of A. gigas. Hearts from A. gigas between 327 and 4040 g weight were used. Collagen fibers were concentrated in regions that were regularly exposed to stress, as elastic fibers showed a broad distribution in all anatomical segments. Several fibrous connections between the conal valve leaflets and the conus arteriosus were observed, possibly acting as the primary connection form. The functions of the connective fibers in the valve leaflets and the bulbus are supported by an extracellular matrix rich in non-sulfated glycosaminoglycans. The complex reticular fiber network in the compact myocardium of the conus and the smooth muscle of the bulbus wall suggests a relevant role in support contraction of both muscle types, and in attachment and mobility of the conal valve leaflets.


Amazonian teleost Collagen Elastin Heart Reticular fibers 



The authors thank the Laboratory of Morphology of Aquatic Organisms, Faculty of Science, Bauru Campus and the Laboratory of Microscopy and Microanalysis, IBILCE, UNESP São José do Rio Preto for technical assistance, and the Federal University of Tocantins, Araguaína Campus, for the heart samples. They also thank Maira Ferrari Munduruca for the manuscript review and the two anonymous reviewers for their helpful comments.


This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Níıvel Superior—Brasil (CAPES)—Finance Code 001 (Process No. 157704).

Compliance with ethical standards

Conflict of interest

All the authors are aware of the policy and have no conflict of interest to declare.

Ethical approval

All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All the procedures performed in this study were in accordance with the ethical standards of the Ethics Committee on Animal Use of the Federal University of Tocantins, Araguaína Campus (Proc. No. 231001.000872/2014-49).


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Zoology, Institute of BiosciencesSão Paulo State University (Unesp)BotucatuBrazil
  2. 2.Department of Biological Sciences, School of SciencesSão Paulo State University (Unesp)BauruBrazil
  3. 3.Aquaculture Center of UnespSão Paulo State University (Unesp)JaboticabalBrazil
  4. 4.Tocantins Federal University (UFT), Araguaína CampusAraguaínaBrazil
  5. 5.Department of Biology, Institute of Biosciences, Humanities and Exact SciencesSão Paulo State University (Unesp)São José do Rio PretoBrazil

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