Stages During the Larval Period
Protruding-mouth stage (72 h):
Modified from:
Kimmel et al., 1995.
Developmental Dynamics 203:253-310. Copyright © 1995 Wiley-Liss, Inc.
Reprinted only by permission of Wiley-Liss, a subsidiary of John Wiley &
Sons, Inc.
EL = 3.5 mm, HTA = 25 degrees. The mouth
is wide open and it protrudes anteriorly just beyond the eye.
The blade of the pectoral fin continues to expand, now extending
posteriorly over most of the length of the diminishing yolk ball
(Fig. 39F).
With Nomarski optics one can see gill slits, and prominent buds
of developing
gill filaments (Fig. 42A), sometimes including
a blood vessel that carries circulating blood. Cartilage cells are
distinctive
in branchial arches 1, 2 (Fig. 42B),
and 5 (Fig.
42C) but not in branchial arches 3 and 4. The primordium of the operculum
extends posteriorly to cover the first or even the second branchial arch. The
first visible bone in the zebrafish, the transversely-oriented
cleithrum
(Fig. 43) now appears, superficial to, and at
the boundary between the first two myotomes. At this location, posterior to
the otic vesicle and last pharyngeal arch, it extends ventrally
into the pectoral
region, where it serves as an anchor of the pectoral fin girdle.
Nomarski optics
are required to see it at this stage; in the young larva it becomes
more prominent.
Histological sectioning shows that the cleithrum is lined with osteoblasts,
but these bone-forming cells are not easily visualized in the living embryo.
A side view with the dissecting microscope now reveals the whole length of
the gut tract behind the pharynx.
Melanin accumulates in the patch overlying the swim bladder
rudiment, making
this region very distinctively darkened. Iridophore coverage of the eye has
expanded to more than half its surface, except for radial stripes,
where black
melanin shows between the golden patches. Iridophores accompany each of the
melanophore stripes, including the yolk stripe. Shortly, the latter
will become
a rather solid reflective band. The yellow cast of the whole dorsal aspect of
the body has increased, so that the hue of the trunk now matches that of the
head.
Circulation in the pharyngeal arch region is becoming more complex with the
advent of gill filament development. A subintestinal vein (Reib,
1973) is variably
present, ventral to the gut tract.
Day 4 stage (96h - 120hh):
A detailed description of this stage is not yet available.
Day 5 stage (120h - 144h):
A detailed description of this stage is not yet available.
Day 6 stage (144h - 168h):
A detailed description of this stage is not yet available.
Days 7-13 stage (7d - 13d):
A detailed description of this stage is not yet available.
Days 14-20 stage (14d - 20d):
A detailed description of this stage is not yet available.
Days 21-29 stage (7d - 13d):
A detailed description of this stage is not yet available.
