In the Heart of a Zebrafish

What am I looking at?

This video initially shows the heartbeat of a 5-day-old zebrafish larva in real time. The video then shows the heartbeat in slow motion. The muscular walls of the heart, which are faint red, surround the green endothelium that lines the heart’s interior. The blood cells flowing through the heart are bright red.

Biology in the background

Zebrafish have a heart and a circulatory system similar to that of humans, but with some important differences. Our hearts have two atria and two ventricles; the atria receive blood from the lungs and the body and pump it into the ventricles, which pump the blood out again to the rest of the body, including the lungs. Zebrafish have only one atrium and one ventricle; however, they have two additional chambers that work with the atrium and ventricle.

In a zebrafish, blood travels from the body to the sinus venosus chamber, which passes it along to the atrium. The atrium then pumps the blood to the ventricle. The ventricle produces very strong contractions that pump the blood into the final chamber, the bulbus arteriosus, which is connected to the aorta – a direct line to the fish’s gills. Once the blood reaches the gills, it’s oxygenated and then distributed to the rest of the body by the forces generated in the ventricle.

An adult zebrafish heart is about 1 millimeter across, or roughly 13 times larger than the width of a human hair. But at the larval stage shown in this video, the heart is only about 250 micrometers across, or roughly three times larger than the width of a human hair.

Technique

This video was created using a form of fluorescence microscopy called light sheet microscopy.