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This chapter covers morphological aspects of the fish heart. It starts with the recognition of the existence of six heart components that are present during embryonic development, and in the adult, and that are anatomically arranged in sequence: sinus venosus, atrium, atrioventricular canal, ventricle, conus arteriosus, and bulbus arteriosus. The anatomy and structure of all the cardiac components are then described and compared between the different fish groups. Data from the basal Cyclostomata, chondrichthyans, basal Osteichthyes, and more advanced teleosts are included and analyzed. Then, data on blood supply to the heart, nerves, and localization of the heart pacemaker are discussed. A separate section at the end of the chapter is committed to the lungfish heart. Lungfishes share many anatomical and functional characteristics with both freshwater fish and amphibians, and the lungfish heart shows some unique and very peculiar characteristics. The enormous diversification of morphological characteristics of the fish heart is emphasized throughout this chapter.

Immunostimulating effects of water extract from bulbus arteriosus in tuna were examined and found to enhance IgM production by human hybridoma HB4C5 cells. When tuna bulbus arteriosus extract was heated, the IgM production-stimulating activity was decreased or lost. To identify the active substance, the extract was partially purified by anion-exchange chromatography, and proteins contained in positive fractions were analyzed by LC-MS/MS. The positive fractions contained lactate dehydrogenase, triosephosphate isomerase, enolase, and haemoglobin. Each of these four proteins was verified to enhance IgM production by HB4C5 cells with the commercially available purified proteins, suggesting that all of these four proteins are active substances in the extract. The immunostimulatory effect of these proteins was also examined on mouse primary spleen lymphocytes in vitro. Lactate dehydrogenase enhanced IgA, IgG, and IgM production and triosephosphate isomerase enhanced IgA and IgG production. In particular, lactate dehydrogenase had the strongest Ig production-stimulating effect on HB4C5 cells and on mouse primary lymphocytes. Thus, fish viscera may serve as an important raw material for the enhancement of the acquired immune system, once processed.

Publisher Summary This chapter discusses the atlas of zebrafish development using the Optical Projection Tomography technique. It explains the whole process through the images containing samples at 96 hours post-fertilization. This is the larval stage. The chapter explains various developmental stages of a larva through different angles using anatomical section views of transverse, sagittal, and coronal. It depicts the development of various organs like the otic vesicle, pectoral fin, immature otolith, gill filaments, olfactory pit, swim bladder, neuromasts, cardiac ventricle, hypothalamus, intestine, bulbus arteriosus, hypothalamus, esophagus, etc.

Publisher Summary This chapter discusses the atlas of zebrafish development using the Optical Projection Tomography technique. It explains the whole process through the images containing samples at 120 hours post-fertilization. This is the larval stage. The chapter explains various developmental stages of a larva through different angles using anatomical section views of transverse, sagittal, and coronal. It depicts the development of various organs like semicircular canal, pectoral fin, pectoral fin musculature, opercular cavity, torus lateralis, granular eminence, semicircular canal, inferior lobe, olfactory pit, intestinal bulb, sternohyoid, posterior intestine, mid intestine, cardiac ventricle, atrium, bulbus arteriosus, pronephros, vertebral column, granular eminence, ventral mandibular arch, etc.

The outflow tract of the heart lies within the pericardial cavity and is the connecting vessel between the ventricle and ventral aorta in all jawed fishes. There is much diversity in the design of the outflow tract among fishes. All display one or even two clearly recognizable forms, a bulbus arteriosus with the wall highly modified for extreme elasticity and a conus arteriosus made up of myocardial muscle. A truncus arteriosus covered in cardiac epithelium, but lacking cardiac muscle in its walls, may occur in some fishes. There is a great amount of diversity in the specific designs, the shapes, and the materials that make up the outflow tract among fishes. For the bulbus, the anatomical form is tuned to maximize its function of providing a continuous flow of blood in the ventral aorta and beyond. The conus may play a minor role in smoothing blood flow but the presence of multiple valves in association with cardiac muscle suggests that the primary function of the conus is in stopping blood flow from the heart. The truncus only occurs in a few species and appears to help keep oxygenated and deoxygenated blood separated in lungfishes.

The basic anatomical plan of the fish heart is an S-shaped arrangement of four cardiac chambers: a sinus venosus, an atrium, a ventricle, and an outflow chamber or tract. The anatomy of these four cardiac chambers is intricately tied to its individual and plays a key role in moving blood continuously around the circulatory system. The sinus venosus is a thin-walled collecting chamber and is the location of the specialized cardiac fibers that initiate the heartbeat. The atrium and ventricle function as muscular pumps that are comprised primarily of cardiac muscle fibers. The ventricle is the main pressure-generating pump for the circulatory system and has the thickest walls. Among other functions, the outflow tract is designed to receive blood from the ventricle at high blood pressure. The diversity that exists among fish reflects phylogeny, function, and environment, with factors as simple as the shape of the fish influencing gross anatomy.

This chapter discusses different aspects of the cardiac anatomy, morphology, and physiology of fish. The fish heart is a four-chambered organ contained within a pericardial sac. Together, the sinus venosus, atrium, ventricle, and either an elastic bulbus arteriosus, or a contractile conus arteriosus raise the potential and kinetic energy of the blood. The principal tissue component of the sinus wall is connective tissue with bounding inner endothelial and outer epicardial linings. The amount of cardiac muscle present in the sinus venosus varies considerably among species. The ventricle shows considerable species variability with respect to its relative mass, gross morphology, histology, and vascularity. The addition of inner fibers, either as a circular arrangement around the sac-like elasmobranch ventricle, or as coils around the vertices of the pyramidal teleost ventricle, is clearly a characteristic of fish that are more active and perhaps provides a mechanical advantage for developing higher blood pressures. The histological structure of the fish coronary artery is characterized by an external parenchyma surrounding a medial layer of vascular smooth muscle; an internal elastic lamina separates the media from the intima, which normally has a single layer of endothelial cells.