Ultimately, the teleost fish heart develops into a classically viewed arrangement of five distinct segments arranged in series: the sinus venosus, atrium, ventricle, conus, and bulbous arteriosus ( Farrell and Jones, 1992 Icardo and Colvee, 2011 Burggren et al., in press). Therefore, a failure in organ development or homeostasis during larval stages could lead to detrimental consequences, if not death, for maturing fishes.Īmong the most critical organ systems is the cardiovascular system, which is the first to function in the larval fishes (indeed, in any developing vertebrate). All organs and their physiological regulation are established during these critical early phases of development. Larval fishes, passing through stages of yolk sac, hatching, opening mouth and free-swimming, are particularly vulnerable to environmental stressors due to their small size, low energy reserves and limited migration capacities. The embryos and larvae of fishes are not simply small juveniles or adults, but rather transitional life forms that bridge the critical gap between the spawned egg and the sexually immature juvenile. However, assessment of heart function-especially if stroke volume is the focus of the study-should consider larval heart shape, with different models being applied on a species-by-species and developmental stage-by-stage basis for best estimation of cardiac output. Essentially, the conventional prolate spheroid shape model provides the simplest measurement with lowest variability of stroke volume and cardiac output. However, when these values of stroke volume multiplied by heart rate to calculate cardiac output, no significant differences between models emerged because of considerable variability in heart rate. End-diastolic and stroke volumes modeled by just a simple cylinder shape were 30–50% higher compared to the conventional prolate spheroid. The conventional prolate spheroid and cone tip + cylinder models yielded significantly different stroke volume values at 56 hpf in red drum and from 56 to 104 hpf in mahi. The inherent error of each model was determined to allow for more precise calculation of stroke volume and cardiac output. The present study assessed the validity of three different heart models (the “standard” prolate spheroid model as well as a cylinder and cone tip + cylinder model) applied to digital images of complete cardiac cycles in larval mahi-mahi and red drum. However, the larval fish heart changes shape during early development and subsequent maturation, but no consideration has been made of the effect of different heart geometries on cardiac output estimation. Cardiac output measurements in transparent fish larvae and other vertebrates have long been made by analyzing videos of the beating heart, and modeling this structure using a conventional simple prolate spheroid shape model. Understanding cardiac function in developing larval fishes is crucial for assessing their physiological condition and overall health. 2Department of Marine Biology and Ecology, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States.1Developmental Integrative Biology Research Cluster, Department of Biological Sciences, University of North Texas, Denton, TX, United States.Prescilla Perrichon 1 * Martin Grosell 2 Warren W.
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