Myocardium Arrangement and Coronary Vessel Distribution in the Ventricle of Three Neotropical Freshwater Teleosts

Abstract

The ventricle of the fish heart is a chamber that exhibits great morphological and vascular variability among species. However, although the Neotropical region has the greatest taxonomic and functional diversity in freshwater fish, many considerations have been formed without previous knowledge of the ventricular morphology of these fishes. Thus, the purpose of the present study was to describe the anatomy, myoarchitecture, and distribution of coronary vessels in the ventricle of three species belonging to two representative groups from this geographical area, Leporinus elongatus, Hoplias malabaricus (Characiformes) and Pterodoras granulosus (Siluriformes), using gross anatomy and light microscopy. The species L. elongatus and H. malabaricus presented a pyramidal ventricle associated to a mixed myocardium, formed by compact and spongy layers. The mixed myocardium was also observed in P. granulosus, but associated with a sac-like ventricle. The compact layer of the species studied was formed by muscular bundles in longitudinal and circular disposition. The spongy layer constituted most of the ventricular myocardium and was formed by a complex network of trabecular sheets presenting muscle fibers also in longitudinal and circular disposition. Coronary vessels were present in the three species and were observed primarily on the surface of the bulbus arteriosus, later branching on the ventricular surface and penetrating the myocardium only at the compact layer level. These characteristics allow classification of the ventricles studied as type II. Although the type I ventricle is the most common type in teleosts, it is important to emphasize that this type has not been observed in any Neotropical freshwater teleosts studied to date.

Heart structure in the Amazonian teleost Arapaima gigas (Osteoglossiformes, Arapaimidae)

“…An association between the pyramidal shape and a compact layer in sedentary species was previously observed in Hoplias malabaricus (Gardinal et al. ) and in the cave‐dwelling population of Astyanax mexicanus (Tang et al. ) but does not appear to be a common association for the teleost heart.…”

“…However, due to its preference for lentic environments and the absence of reproductive migration, this species is classified as sedentary (Isaac et al 1993;Castello, 2008). An association between the pyramidal shape and a compact layer in sedentary species was previously observed in Hoplias malabaricus (Gardinal et al 2018) and in the cave-dwelling population of Astyanax mexicanus (Tang et al 2018) but does not appear to be a common association for the teleost heart. Therefore, although A. gigas does not have an active lifestyle, the pyramidal ventricle associated with the compact layer in the myocardium could be necessary to support its rapid growth rate (Castello, 2008).…”

“…Based on our results, we can classify the ventricle of A. gigas as type II. Only the type II ventricle has been observed in Neotropical freshwater teleosts, even in sedentary species (Simões et al 2002;Gardinal et al 2018;Tang et al 2018). However, since little published information is available, more studies are necessary to understand the evolution of the ventricle and the coronary circulation in species from this region, which harbors the highest taxonomic and functional diversity of freshwater fish (Toussaint et al 2016).…”

Ontogenetic changes in the body structure of the Arctic fish Leptoclinus maculatus

“…Thus, the heart of L. maculatus belongs to the type-I, which is the most common in Bony fishes. In C. hamatus the ventricle was entirely trabeculated 38,39,45,46 . However, the organization and ventricle type can change during the ontogeny.…”