Abstract
Understanding cardiac function in developing larval fishes is crucial for assessing their physiological condition and overall health. 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. 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. 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. The inherent error of each model was determined to allow for more precise calculation of stroke volume and cardiac output. 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. End-diastolic and stroke volumes modeled by just a simple cylinder shape were 30–50% higher compared to the conventional prolate spheroid. 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. Essentially, the conventional prolate spheroid shape model provides the simplest measurement with lowest variability of stroke volume and cardiac output. 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.
Highlights
The embryos and larvae of fishes are not small juveniles or adults, but rather transitional life forms that bridge the critical gap between the spawned egg and the sexually immature juvenile
While substantial species-specific differences in details of cardiac form exist between adults of different fish species, many cellular and molecular processes that underlie especially early cardiac development are highly conserved in all vertebrates, and across teleost fishes (Bakkers, 2011; Liu and Stainier, 2012)
This study has considered changing cardiac form during cardiogenesis to develop potentially more precise quantification of ventricular blood pumping in larval teleost fishes
Summary
The embryos and larvae of fishes are not small juveniles or adults, but rather transitional life forms that bridge the critical gap between the spawned egg and the sexually immature juvenile. Heart Modeling in Larval Fishes limited migration capacities. All organs and their physiological regulation are established during these critical early phases of development. Among the most critical organ systems is the cardiovascular system, which is the first to function in the larval fishes (in any developing vertebrate). While substantial species-specific differences in details of cardiac form exist between adults of different fish species, many cellular and molecular processes that underlie especially early cardiac development are highly conserved in all vertebrates, and across teleost fishes (Bakkers, 2011; Liu and Stainier, 2012). The heart, responsible for blood convection, must respond to the rapidly changing demands of the developing larvae, including an initial role in angiogenesis followed by transport of respiratory gases (O2), nutrients (e.g., amino acids, carbohydrates, fats), cellular waste products, regulators (e.g., hormones, molecular chaperones), and pressure (arterial circulation) (Burggren, 2013; Burggren et al, in press)
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