Frontal view of cavefish and zebrafish embryos

Confocal micrograph of a cavefish (left) and a zebrafish (right) embryo viewed from the front showing the head. Both embryos are stained with fluorescent antibodies; one targets a calcium binding protein (calretinin) shown in yellow and blue, the other marks a tight junction component (zona occludens 1) shown in pink. Calretinin labels different cell types in the brain and sensory organs. Taste buds are labelled around the mouth in both embryos (yellow in the cave fish and blue in the zebrafish). Zona occludens 1 is used to reveal tissues with an epithelial organization, such as the ventricular surface in the brain in both fish. Researchers can learn a lot about development by comparing different organisms and the cavefish is often used in studying evolutionary development. Cavefish live in total darkness so adult cavefish are blind. The eyes develop during early embryonic stages but degenerate later on.