Bulletin of the Sea Fisheries Institute 2 (156) 2002 - CEEMaR

48 K. FORMICKI, A. KORZELECKA-ORKISZ, M. BONIS£AWSKA, A. TAÑSKI, W. WAWRZYNIAK and A. WINNICKI
RESULTS
Water absorption and the creation of the perivitelline space lasted for about two hours at a
temperature of 12.8°C (Fig. 1; Fig. 2 a-c) and it was completed at the moment the first cell
division occurred (Fig. 2e). At this moment, the perivitelline space constituted almost 70% of
the volume of the swollen, hydrated egg.
The egg cells (yolk sphere) which were observed from the side retained their regular
spherical shapes, and the diameters of eggs obtained from the same female were 0.78 ±0.024
mm ( x ±SD), with a volume of 0.25 ±0.022 mm 3 ( x ±SD).
Herring eggs with their thin, transparent membranes, are covered by a adhesive, gelatinous
substance which ensures that the eggs stick firmly to the substrate and that they cling
together in an aggregation (Fig. 3). The shape of the eggs that comprise the aggregations are
usually irregularly angular, while individual eggs retain their regular spherical shape.
The diameter of the swollen eggs of the Baltic herring was small at 1.31±0.025 mm
( x ±SD) and the volume was 1.17±0.067 mm 3 ( x ±SD). However, there are significant, individual
differences. The diameter of the smallest eggs from the same female was 1.23 mm, while
that of the largest was 1.37 mm. The volume varied from 0.97 mm 3 to 1.35 mm 3 , respectively;
thus, the difference in the volume of the large and small eggs was almost 1.4-fold.
It was characteristic that size diversity, including egg size, was not reflected in the size of
the egg cells (yolk sphere), covered by a thin layer of ectoplasma at the moment they are laid,
and which are uniform in eggs of different sizes.
The reception mount is formed after about 1h 10 min. (15 h o ) from the moment of activation
(Fig. 2d). The ectoplasma usually collects at the side in the equatorial zone of the egg. This
side position in the egg is maintained throughout embryogenesis (Fig. 2e-i).
The course of embryogenic develpment, or the sequence of major structural changes from
the activation of the egg cell until hatching, are presented in the photographs in figures 2a-l.
Embryonic locomotion follows a specific pattern, clearly visible on the videotapes
made in vivo, which recorded the characteristic regularity of the primal plasmatic movements
which occur directly after activation and lead to the creation of the germinal disk, to
the first, very slow, range-limited somatic movements in the trunk portion of the body of
the embryo, the frequency of which decreases as hatching draws nearer, up to the pulsation
of the budding heart (63 h – 820 °h) and then the formed heart at approximately 83 h
(1080 h°) (Fig. 4);
Larval sizes. The length of newly hatched larvae was diverse and varied from 4.86 to
6.32 mm, with an average of 5.59±0.52 ( x ±SD), while the average volume of the yolk sac,
which decreased as larval length increased, was v = 0.096 ±0.03 mm 3 ( x ±SD).
In addition to the important results above, the figures also present the following:
– unlike other teleost fish, herring egg cells (yolk spheres) are similar in size at the
moment of activation and there is no correlation between their size and that of the egg, which is
highly diverse;
– the lack of structural fat in the egg cell and also in the yolk allows the germinal disk to
assume a side position which is the origin of the future structures of the specimen;
– the lack of red blood dye – hemoglobin – in the morphotic elements of the blood
during embryogenesis;
– the change in the yolk sac shape from a regular sphere until hatching to longitudinal,
slightly flattened oval (Fig. 4) which resorbs very slowly (6-7 days, temp. 13.1°C);