Table of Stages

Staging Series for Embryonic Zebrafish Development

(After Kimmel et al, 1995)
Stage

Length of
Incubation
(28.5°C)
Description of embryo
Fertilization 0 hours Newly fertilized egg undergoes cytoplasmic streaming producing blastodisc at animal pole.
Cleavage 45 minutes - 2 hours Cleavage begins after 45 minutes, and continues synchronously at 15-minute intervals.

2-cell
(1st cleavage)

45 minutes Cleavage is meroblastic. (incomplete), the two cells are continuous with the yolk.

4-cell
(2nd cleavage)

1 hour Cleavage is meroblastic, cells are arranged in 2 rows of 2 cells per row (2X2).

8-cell
(3rd cleavage)

1 1/4 hour Cleavage is meroblastic, cells are arranged in 2 rows of 4 cells per row (2X4).

16-cell
(4th cleavage)

1 1/2 hour Cleavage outer cells is meroblastic, central 4 blastomeres are complete. Cells are arranged in 4 rows of 4 cells per row (4X4).

32-cell
(5th cleavage)

1 3/4 hour Cleavage is complete of non-marginal blastomeres. Cells are not always arranged regularly, though can be in 4 rows of 8 cells per row (4X8). In side view appears to be two tiers of cells.

64-cell
(6th cleavage)

2 hours Horizontal cleavage planes produce two tiers of cells, though in side view it appears to be three tiers.
Blastula 2 1/4 – 3 1/2 hours Embryo continues to divide, becoming metasynchronous, adding tiers of blastomeres.

128-cell
(7th cleavage)

2 1/4 hour Cells sit as a high mound in five irregular tiers.

256-cell
(8th cleavage)

2 1/2 hours Cells are seen as seven tiers.

~1000-cell
(10th cleavage)

3 hours Yolk syncytial layer (YSL) forms. About 11 tiers of cells can be seen.
High 3 1/3 hours Blastoderm is a high mound of cells. More than 11 tiers of cells can be seen.
Oblong 3 2/3 hours Blastoderm begins to flatten so that the egg looks oblong.
Sphere 4 hours The blastoderm continues flattening until the egg becomes spherical.
Dome 4 1/3 hours A short period during which the internal YSL domes upward toward the animal pole. This marks the beginning of epiboly, the movement of the blastoderm down around the yolk.
30% epiboly 4 2/3 hours Epiboly continues, reaching 30% of the distance between the animal and vegetal poles.
Gastrula 5 1/4 – 10 hours Epiboly continues and the body plan becomes apparent.
50%-epiboly 5 1/4 hours Epiboly continues as gastrulation movements within the deep layer of cells separating the germ layers into an upper epiblast and lower hypoblast.
Germ-ring 5 2/3 hours The germ ring becomes visible at 50% epiboly
Shield 6 hours Embryonic shield forms
90%-epiboly 9 hours Brain rudiment is thickened by 90% epiboly
Bud 10 hours Tail bud forms and epiboly is complete.
Segmentation 10 1/3 – 22 hours Somites are forming.
1-somite 10 1/3 hours First somite forms.
5- somite 11 2/3 hours By the 5-somite stage optic vesicle is prominent.
14-somite 16 hours By the 14-somite stage the otic placode is visible as are the brain neuromeres, and the trunk somites have a V-shape.
20-somite 19 hours By the 20-somite stage (19 hours), muscular twitches are evident, the otic placode is now an otic vesicle, the eye lens is evident, hindbrain neuromeres are prominent, and the tail is well extended.
26-somite 22 hours By the 26-somite stage (22 hours), the embryo flexes side to side. Otoliths can be seen in the inner ear (otic vesicle).
Pharyngula 24 – 42 hours Pigmentation is developing.
Prim-5 24 hours By the Prim-5 stage, pigmentation in the pigmented retina of the eye as well as in the skin becomes apparent, the heart begins beating, and red blood cells can be seen in the yolk sac (24 hours).
Prim-15 30 hours By the Prim-15 stage, the embryo responds to touch, and spontaneous movements are reduced. The retina is well pigmented. The caudal artery extends halfway to the tail (30 hours).
Prim-25 36 hours By the Prim-25 stage, there is tail pigmentation, blood circulation is strong, a single aortic arch can be seen, and the caudal artery extends three-quarters of the way to the end of the tail (36 hours).
High-pec 42 hours By the High-pec stage, a dechorionated embryo rests on its side after swimming. There is a complete dorsal stripe, xanthophores can be seen in the head region and iridophores in the retina. The mandibular and hyoid arches are visible (42 hours).
Hatching 48 – 72 hours Hatching occurs asynchronously.
Long-pec 48 hours By the Long-pec stage, dorsal and ventral stripes meet at the tail. Iridophores are numerous in retina, head has a distinct yellow cast to it. 2-4 aortic arches can be seen with circulation in them (48 hours).
Pec-fin 60 hours By the Pec-fin stage, movements are very rapid, the pectoral fin is flattened into a fin shape. Iridophores are seen in the dorsal stripe, early jaw cartilages are visible, and circulation can be seen in the 5-6 aortic arches (60 hours).
Protruding-mouth 72 hours By the Protruding-mouth stage, the mouth is wide open and protrudes anterior to the eye. The dorsal body is as yellow as the head. Gill slits can be seen, and cartilage is present in the branchial arches (72 hours).
Source: Kimmel, C. B., W. W. Ballard, S. R. Kimmel, B. Ullmann, and T. F. Schilling. 1995. Stages of embryonic development of the zebrafish. Dev. Dyn. 203: 253-310.