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SEM image of the week: Zebrafish embryos

Posted on Monday, March 5, 2012 by for SEM.

Tammy Jiang holds an Eppendorf tube containing about a dozen zebrafish embryos. The embryos are barely visible at the bottom.

Aptly named after the zebra for its black and white stripes streaked across its body, the zebrafish (Danio rerio) is a fascinating model to study for research in developmental genetics. Zebrafish are used to understand the roles of genes and the various processes and mechanisms that the embryo undergoes during development to form vital organs, tissues, and other structures. Zebrafish embryos are ideal for this research because fertilization and development occur outside of the womb, which allow scientists to observe and experiment on them. Another feature that makes them useful as a genetic model organism is their transparency; scientists can actually see individual cells during development under a microscope. In addition, zebrafish embryos mature rapidly (primary organs are formed after 24 hours), making research less time consuming. With zebrafish embryos, scientists discover new and important genes, understand what causes birth defects, and essentially research how a fully functional organism comes into being.

32 hours post fertilization False color image: yellow yolk, light blue body, dark blue eyes.

Female zebrafish lay eggs daily. These eggs start out as single cell stage embryos and then the cells divide. The blastula stage lasts three hours and gastrulation is completed in five hours. Epiboly is a cell movement that is a thinning and spreading of three layers that will eventually form into the ectoderm, mesoderm, and endoderm germ layers. Somite morphogenesis first occurs around 10 hours post fertilization (hpf). Somites are body segments that increase in number as development happens and are used as indicators of the different stages of embryonic development. The tail of the zebrafish embryo develops at the 15 somite stage (16.5 hpf). The embryo feeds off of its yolk sac, which looks like a big yellowish ball in its belly region. The embryo will hatch from its eggshell 72 hpf and will look for food two days after that. By the time the yolk sac disappears, it will start hunting for food.

6 hours post fertilization, somite stage 32 hours post fertilization
36 hours post fertilization

Image and text credit: Tammy Jiang