Concretia is a developing zebrafish embryo. Over the course of 8 days, the following developments were observed: - By day 2, optic buds began to form and Kupffer's vesicle was enlarging. - On day 3, a heartbeat was detected at around 59 beats per minute. Blood vessels and veins also began to form. - By day 8, the heartbeat had increased to 148 beats per minute. Internal organs such as the swim bladder and eyes had developed further, and the notochord was completely vacuolized along the tail.

1. Meet Concretia Late Neurula stage (Optic bud formation) Stage: 18 26 hours old! --Kupffer’s vesicle is beginning to form and is enlarging. Anterior end of the keel has broadened into two divisions of the rudimentary brain. The embryonic axis about 1 mm in length and the mesodermis is reducing laterally. A solid optic bud (rudimentary eye vesicle) appears on each side. The beak-like cell mass is still visible. A small part of the yolk sphere still forms a blastophore at the vegetal pole, but is only a small opening.

2. Concretia Day 2 Not much of Concretia has changed. She is getting easier to see, and her structures more visible to us. By the next day we predict to be able to see a beating heart.

3. Day 3:Start of a HeartBeat! Stage: 23 46 Hours Old! Somite Stage There is a heartbeat! Around 59 beats per minute. The anterior portion of the straight-tubed heart reaches beneath the posterior end of the eye vesicle. A pair of semi-circular blood vessels and the vitello-caudal vein begin to form on the yolk sphere. Kupffer’s vesicles shrink. The neuro-coele is formed in the fore-, mid- and hind-brains. The spherical optic lenses are form completely. Around 15 somites are formed. A blood island becomes pronounced in the ventral region. The oil droplets have formed into a single large drop.

4. Day 8 144 hours old Stage: 33 Notochord Vacuolation Many internal organs haven’t been developed. The swim bladder now appears very small as a clear vesicle mesial to the urinary bladder. Her heartbeat increased to about 148 beats per minute. The eyeballs (choroidea) are very dark, and are cute. The notochord is completely vacuolized to the end of the tail. The pineal gland is distinct at the dorsal surface of the vascularized forebrain. The tips of the membranous margins of the pectoral fins reach the 4 th somite.