It’s starting! We’ve got another batch of fertilized eggs, now here at the lab instead of our satellite facility– they are developing more comfortably at highly controlled temperatures in our new incubator. You can see one of our new eggs here, about 14 hours after fertilization.
In fish, development is discoidal meaning that the entire egg doesn’t divide, rather a thin layer of cells on the “top” of the egg– this portion is called the blastodisc. The cells of the developing fish are located in the upper right hand portion of the image. As development continues, this layer of cells will “flatten” and eventually encircle the yolk of the egg. As the cells divide more and more, they start to move (or epiboly)toward the “bottom” of the egg through a process known as gastrulation. Lewis Wolpert famously said “It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life.” How true! As this process moves to about halfway down the cell in a few hours, the cells that will eventually become all major organ systems will have begun to differentiate. Eventually, the blastula will complete epiboly sometime tomorrow morning, and the first signs of a discernible fish will be visible.