Modified from:
Kimmel et al., 1955.
Developmental Dynamics 203:253-310. Copyright © 1995 Wiley-Liss, Inc.
Reprinted only by permission of Wiley-Liss, a subsidiary of John Wiley &
Sons, Inc.
Table 2: Stages of Embryonic Development
Stage - h - HB - Description
Zygote period
1-cell - 0 - 1,2 - Cytoplasm streams towards animal pole to form the blastodisk
Cleavage period
2-cell - 3/4 - 3 - partial cleavage
4-cell - 1 - 4 - 2 x 2 array of blastomeres
8-cell - 1 1/4 - 5 - 2 x 4 array of blastomeres
16-cell - 1 1/2 - 6 - 4 x 4 array of blastomeres
32-cell - 1 3/4 - 7 - 2 regular tiers (horizontal rows) of blastomeres, sometimes in 4 x 8 array
64-cell - 2 - 8 - 3 regular tiers of blastomeres
Blastula period
128-cell - 2 1/4 - 9 - 5 blastomere tiers; cleavage planes irregular
256-cell - 2 1/2 - - 7 blastomere tiers
512-cell - 2 3/4 - - 9 tiers of blastomeres; NO: YSL forms
1k-cell - 3 - 10 - 11 tiers of blastomeres; NO: single row of YSL nuclei; slight blastodisk cell cycle asynchrony
High - 3 1/3 - - >11 tiers of blastomeres; beginning of blastodisk flattening; NO: YSL nuclei in two rows; substantial division asynchrony
Oblong - 3 2/3 - 11 - Flattening produces an elliptical shape; NO: multiple rows of YSL nuclei
Sphere - 4 - 12 - Spherical shape; flat border between blastodisk and yolk
Dome - 4 1/3 - 13 - Shape remains spherical; yolk cell bulging (doming) towards animal pole as epiboly begins
30%-epiboly - 4 2/3 - 14 - Blastoderm an inverted cup of uniform thickness; margin reaches 30% of distance between the animal and vegetal poles
Gastrula period
50%-epiboly - 5 1/4 - - Blastoderm remains uniform in thickness
Germ-ring - 5 2/3 - - Germ ring visible from animal pole; 50%-epiboly
Shield - 6 - 15 - Embryonic shield visible from animal pole, 50%-epiboly
75%-epiboly - 8 - 16 - Dorsal side distinctly thicker; epiblast, hypoblast, evacuation zone visible
90%-epiboly - 9 - - Brain rudiment thickened; notochord rudiment distinct from segmental plate
Bud - 10 - 17 - Tail bud prominent; notochord rudiment distinct from neural keel; early polster; midsagittal groove in anterior neural keel; 100%-epiboly
Segmentation period
1-somite - 10 1/3 - - First somite furrow
5-somite - 11 2/3 - 18 - Polster prominent; optic vesicle, Kupffer's vesicle
14-somite - 16 - 19 - EL = 0.9 mm; otic placode; brain neuromeres, v-shaped trunk somites; YE barely forming; NO: pronephric duct
20-somite - 19 - 20 - EL = 1.4 mm. YE/YB > 0.5 and < 1; muscular twitches; lens, otic vesicle, rhombic flexure; hindbrain neuromeres prominent; tail well extended
26-somite - 22 - - EL = 1.6 mm; HTA = 125 degrees; Side-to-side flexures; otoliths; Prim-3
Pharyngula period
Prim-5 - 24 - - EL = 1.9 mm; HTA = 120 degrees; OVL = 5; YE/YB = 1; early pigmentation in retina and skin; median fin fold; red blood cells on yolk, heart beat
Prim-15 - 30 - - EL = 2.5 mm; HTA = 95 degrees; OVL = 3; YE/YB > 1; YB/HD = 2; early touch reflex and reduced spontaneous movements; retina pigmented; dorsal stripe to somite 12; weak circulation; caudal artery halfway to end of tail; caudal vein braided; shallow pectoral fin buds; straight tail; NO: cellular degeneration at end of tail; circulation in aortic arch 1
Prim-25 - 36 - - EL = 2.7 mm; HTA = 75 degrees; OVL = 1; PF(H/W) = 3/4; early motility; tail pigmentation and ventral stripe filling out; strong circulation; single aortic arch pair; caudal artery is 3/4 of the way the to the end of tail; pericardium not swollen; NO: PF apical ectodermal ridge
High-pec - 42 - - EL = 2.9 mm; HTA = 55 degrees; OVL < 1 and > 1/2; YE/YB = 1.5; YB/HD < 1.3; PF(H/W) = 1; dechorionated embryos rest on side after swimming; YE remaining cylindrical; PF apical ridge prominent; early lateral stripe; complete dorsal stripe; xanthophores in head only; iridophores in retina only; pericardium prominent; HO: heart chambers; segmental blood vessels; mandibular and hyoid arches; foregut developments olfactory cilia; thickened otic vesicle walls
Hatching period
Long-pec - 48 - - EL = 3.1 mm; HTA = 45 degrees; OVL = 1/2; PF(H/W) = 2; resting dorsal up; YE beginning to taper; PF pointed; dorsal and ventral stripes meet at tail; ca. 6 melanophores in lateral stripe; iridophores plentiful on retina; distinct yellow cast to head; NO: circulation in 2-4 aortic arches and in segmental vessels; olfactory cilia beating; semicircular canals; neuromasts
Pec-fin - 60 - - EL = 3.3 mm; HTA = 35 degrees; movements too rapid to resolve; YB tapering into YE; up to 10 melanophores in lateral stripe; PF flattenened into fin shape with prominent circulation; iridophore retinal ring fills out; iridophores in dorsal stripe; NO: PF cartilage and actinotrichia; gut tract; 2 chambers in otic vesicle; early jaw cartilages; circulation in 5-6 aortic arches; mouth remaining small and open at ventral location midway between eyes
Protruding-mouth - 72 - - EL = 3.5 mm; HTA = 25 degrees; wide open mouth protruding anterior to eye; iridophores in yolk stripe; eye half covered by iridophores; dorsal body as yellow as head; NO: gill slits and filament buds; cartilage in branchial arch 1 and 5; operculum covers the branchial arch 1 or 2; cleithrum
Abbreviations: EL: embryo length, PF: pectoral fin, h: hours of development at 28.5C. HB: approximate stage number in the Hisoaka & Battle (1958) zebrafish staging series (reasonably accurate through HB stage 20), HD: head diameter in dorsal view, NO: Nomarski optics, H/W: height/width, Prim: Prim stages refer to the number of the myotome to which the leading end of the posterior lateral line primordium has advanced. YB: yolk ball, YE: yolk extension, YSL: yolk syncytial layer
