Showing papers in "Fish Physiology in 2017"

Heart Morphology and Anatomy

Abstract: 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.

Form, Function and Control of the Vasculature

Abstract: This chapter summarizes the form, function, and control of the blood vasculature in fish. It starts with a general overview of the gross anatomy of the vascular system. We then turn to the arterial vasculature and the hemodynamic principles governing vascular resistance and arterial blood pressure, including a summary of the main local, neural, and hormonal systems controlling arterial resistance. The highly specialized vascular system of the gills (i.e., the branchial circulation) is covered in a separate section where we describe their complex microvascular arrangements, as well as the control mechanisms of both the arterioarterial (“respiratory”) and arteriovenous pathways. The chapter closes with a comprehensive overview of the venous vasculature. This includes the hemodynamic principles determining venous return, the importance of central venous blood pressure for cardiac performance, and the neurohumoral control mechanisms of venous capacitance and compliance. Finally, we discuss the importance of venous hemodynamic changes during integrated cardiovascular responses such as exercise and barostatic reflexes, and in response to changes in environmental variables including temperature, oxygen availability and salinity. While the chapter, by necessity, is biased toward teleosts due to the more abundant literature for that group, information on elasmobranchs, cyclostomes, and air-breathing fishes is also provided to highlight similarities and differences among the major groups of fish.

Cardiac Energy Metabolism

Abstract: The heart must provide its own energy requirements to sustain its continuous contractile performance and other physiological functions. This chapter provides an integrated overview of cardiac energy metabolism in fish with a particular emphasis on: maintenance of cardiac energy state; biochemical strategies for energy production; and energetic requirements to maintain contractile function, ion pumping across membranes, and protein synthesis. Major advances in our understanding of fish cardiac metabolism have come from studies of cellular ultrastructure, ion regulation, enzyme activities, select proteins involved in energy metabolism, fuel selection and energy reserves, intracellular metabolites, cardiac adaptability, and physiological performance of cardiac preparations and intact animals. Total energy expenditure of the contracting heart varies between species and includes basal and active components. The importance of myosin-bound ATP phosphatase (ATPase) for contractility, Na+/K+-ATPase for cellular ion homeostasis, and Ca2 +-ATPases for myocardial relaxation are highlighted. Fish hearts rely on well-established metabolic pathways to regenerate ATP, however, species differences are apparent. Under normoxic conditions, mitochondria produce most of the ATP used by the fish heart using aerobic metabolism and a variety of energy substrates. However, during O2-limiting conditions, anaerobic metabolism (glycolysis) becomes the major source of ATP production, despite an inherently limited capacity compared with oxidative phosphorylation. Cold temperature can also compromise several cellular processes related to cardiac energy metabolism, and yet, some fish demonstrate positive compensation of enzyme activities following cold acclimation and acclimatization. Overall, there are numerous, inter-related factors that underlie cardiac energy production and utilization.