This lab will give you the opportunity to see cleavage divisions as they occur and to recognize significant stages of embryonic development of a simple vertebrate. The zebrafish, Danio rerio, is a common aquarium fish that breeds very easily. If fish are maintained in breeding condition, spawning occurs each day at dawn, and with fertilization external, all stages are easily accessible. The embryo and its outer shell are very clear optically, allowing for easy observation throughout its early development. The small size of the embryo allows you to section very deeply into the embryo with slight focus adjustments of the microscope to reveal much of the internal structural development.
Development is also very rapid.
18 hrs heartbeat and pigmentation 24 hrs swimming 48 hrs hatching and feeding 72 hrs Part I. Observations of the Cleavage Period During this period, the first 6 cleavages occur. The cells, or blastomeres divide synchronously at about 15 minute intervals. You can easily observe these early cleavages with the dissecting microscope, using transmitted light. Usually, the first five cleavages are all vertical and occur at right angles to one another, as shown in the figure below. Figure 2 View is from the animal pole with cleavage planes numbered.