Embryonic Onset of Sexually Dimorphic Heart Rates in the Viviparous Fish, Gambusia holbrooki

In fish, little is known about sex-specific differences in physiology and performance of the heart whether these manifest during development. Here for first time, rates embryogenesis Gambusia holbrooki, from onset (HRs) to just prior parturition, was investigated using light cardiogram. The genetic sex embryos post-verified a marker. Results reveal that resting time significantly increase (p < 0.05) with progressive embryonic Furthermore, both ventricular atrial frequencies female were higher than those their male sibs at corresponding developmental stages remained so all later 0.05). concurrence, rate size adult females also larger respectively males. Collectively, results suggest cardiac sex-dimorphism manifests as early late-organogenesis persists through adulthood this species. These findings measurements can be employed non-invasively developing embryos, well advance when phenotypic discernible. addition, G. holbrooki could serve better model study comparative vertebrate cardiovascular development investigate anthropogenic climatic impacts on species, may influenced.