This image captures the bright blue light (chemiluminescence) emitted by the NanoLuc protein in LipoGlo zebrafish. By attaching this glowing enzyme to bad-cholesterol particles, researchers are able to visualize how much cholesterol is present in each fish, and where in the body it resides. The top image shows a zebrafish embryo 24 hours into development, with many cholesterol particles emanating from its large spherical yolk. Subsequent images were taken every 24 hours, showing that cholesterol levels peak between three and four days of age in zebrafish embryos.