Basic HTML Version
Inter. J. of Marine Science 2012, Vol.2, No.4, 24-30
http://ijms.sophiapublisher.com
27
2 Discussion
Trends in GSI revealed two distinct spawning peaks for
S. sutor
, a short peak in June-July and a more
protracted peak from November to January/February.
The month of October was observed as the likely
period when the onset of ovary maturation occurs.
These results concur with previous work on spawning
seasonality of
S. sutor
by Ntiba and Jaccarini (1990),
who also found two distinct peak spawning seasons for
S. sutor
in Kenyan waters (Table 1). In contrast, the
current findings differ from those of de Souza (1988),
which showed that
S. sutor
spawns throughout the year
in Kenyan inshore waters. Tanzanian populations of
S.
sutor
exhibit a less protracted spawning season than
populations in Kenya (Table 1; Kamukuru, 2006). The
difference in results may be explained by parameters
like condition factor used in the other studies, which
was assumed to relate to maturation schedules.
Table 1 Macro- and microscopic criteria of female gonadal development (modified from de Souza, 1988; Ntiba and Jaccarini, 1990;
Samoilys and Roelofs, 2000; West, 1990)
Development
stage
Microscopic oocyte stage
Microscopic: :
other criteria
Macro-stage description
Macro-stage
no
Immature, IM
Pre-vitellogenic oocytes:
Oogonia, chromatin nucleus,
early perinucleolus stains darkly,
late perinucleolus stains faintly,
oocytes irregularly shaped with
no defined cell membrane
No sign of prior spawning:
Thin gonad wall, compact,
lamellae well packed,
no cytoplasmic vacuoles
Gonads thin and threadlike, running
longitudinally along dorsal wall of
the body cavity, sex indeterminate
Ⅰ
Resting, RE
Pre-vitellogenic oocytes (as
above):
Residual atretic oocytes present,
cytoplasmic vacuoles
Thick wall, lamellae not
compact, often vacuolated,
few rounded oocytes
brown bodies
Ovaries are cylindrical and pinkish
tapering gradually toward posterior
end, and occupy half the body
cavity
Ⅱ
Mature, RI
Vitellogenic oocytes:
Yolk vesicle, early and late
yolk globule, migratory Nucleus
stage
May have atretic oocytes,
may have post-ovulatory
follicles (POFs) from
previous spawning
Ovaries are opaque and yellowish
with some large oocytes clearly
visible; Ovaries fully swollen with
Oocytes clearly visible, heavy
network of blood vessels appears
on the surface of ovary wall
Ⅲ
Ⅳ
Running ripe,
RR
Hydrated oocyte:
Yolk granules in the cytoplasm,
defined striated cell membrane
Final stage of oocyte
development leading to
egg release. Ovulation
results in ruptured or
empty POFs
Ovaries are very soft and swollen:
translucent and full of water; slight
pressure on abdomen produces eggs
at the vent, yellowish in color due
to large yellow oocytes, blood
vessels coalesce to form large ones
on the external of ovary wall
Ⅴ
Spent, SP
Atretic vitellogenic oocytes:
Pre-vitellogenic oocytes, dense
network of blood vessels
Lamellae disrupted and
remnant late-stage oocytes
and prominent muscle
bundles present
Ovaries are small, flaccid, wrinkled
and very red with loose follicular
tissue
Ⅵ