title: Anatomical, histochemical and immunohistochemical characterisation of the cardiac outflow tract of the silver arowana, Osteoglossum bicirrhosum (Teleostei: Osteoglossiformes).
abstract: The cardiac outflow tract of chondrichthyans and actinopterygians is composed of a myocardial conus arteriosus and a non-myocardial bulbus arteriosus. In teleosts, the conus has been subjected to a reduction in size over the evolution in conjunction with the further development of the bulbus. Most studies on the outflow tract of the teleost heart refer to species of modern groups and are mainly devoted to the bulbus. Knowledge on the outflow tract of species belonging to early teleost groups is scarce. The aim here was to characterise the structure of the cardiac outflow tract of the silver arowana, a representative of the ancient teleost clade of the Osteoglossomorpha. The material consisted of hearts from six juvenile animals. The cardiac outflow tract of the silver arowana is composed of a conus, which supports two conal valves, and a bulbus. Both components are lined externally by the epicardium and internally by the endocardium. The conus is immunoreactive to antibodies against myosin heavy chains and is composed of compact myocardium, thus contrasting with the ventricle, which has exclusively trabeculated myocardium. The bulbus is immunoreactive to antibodies against smooth muscle α-actin and mainly consists of elastic fibres and smooth muscle cells, both arranged in three layers, outer, middle and inner. The most remarkable feature of the bulbus is the presence of two prominent longitudinal ridges, dorsal and ventral, at the luminal side, which serve to anchor the commissures of the conal valves. This arrangement has not been described so far in any fish species. Pigment cells, presumably of neural crest origin, are present in the subepicardium of the bulbus and anterior part of the ventricle.
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Lorenzale
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: López-Unzu
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain; Biomedical Research Institute of Málaga (IBIMA), University of Málaga, 29071 Málaga, Spain.
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Fernández
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain; Biomedical Research Institute of Málaga (IBIMA), University of Málaga, 29071 Málaga, Spain.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Durán
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain; Biomedical Research Institute of Málaga (IBIMA), University of Málaga, 29071 Málaga, Spain.
authors.forename: Borja
authors.initials: B
authors.lastname: Fernández
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain.
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Soto-Navarrete
authors.affiliation: Department of Animal Biology, Faculty of Science, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain; Biomedical Research Institute of Málaga (IBIMA), University of Málaga, 29071 Málaga, Spain. Electronic address: sanscoma@uma.es.
authors.forename: Valentín
authors.initials: V
authors.lastname: Sans-Coma
mesh_terms: D000818:Animals; D003331:Coronary Vessels / Q000033:anatomy & histology*; D005399:Fishes / Q000033:anatomy & histology* / Q000502:physiology*; D007150:Immunohistochemistry
keywords: Bulbus arteriosus; Conus arteriosus; Heart; Heart pigmentation; Osteoglossum bicirrhosum