Biology Reference
In-Depth Information
subjected to MT-treatments between 14-63 dph and between 320-500 dph
have not reversed the sex (Hunter and Donaldson, 1983). Even when the
entire gonads along with the mesentery have been removed, the female and
male grass carps regenerate ovary and testis alone, respectively. Clearly,
this experimental evidence reveals that the sex is irrevocably determined
at the embryonic/juvenile stage (prior to 14 dph) and not only in their
gonads and brains but also the entire fi sh has been sexualized (i.e., in terms
of Zarkower, 2006). In the total absence of gonads including mesentery,
the gonads can be completely regenerated from other organ system, i.e.,
the PGCs, OSCs or SSCs and germ cells supporting cells can be derived
from an organ system that is entirely outside the purview of the gonad.
O. niloticus
is also amenable to almost 100% masculization or feminization,
provided the respective hormone treatment is synchronized within the
labile period of upto 30-45 dph (e.g., Gale et al., 1999). Subsequently, sex
is decisively determined and is not altered on gonadectomy. This is true of
O. nerka
also. Castrated genetic male (XY)
O. mykiss
regenerates only the
testis, irrespective of receiving E
2
-treatment or not. However the castrated
neomale (XX) too regenerates testis, indicating the stability of sex of the
gonad that has earlier been sex reversed by exposure to exogenous androgen,
i.e., it does not re-revert to the genotypic sex during the regenerative
process. This implies that the sex of
O. mykiss,
once determined genetically
or hormonally, remains stable and adults retain unisexual potency alone.
The castrated
Gambusia affi nis
regenerates gonopodium even in presence of
the small testis, indicating that in
G. affi nis
too sex determination is a stable
process. Dietary administration of one or other androgen even at relatively
high doses to gravid
Poecilia reticulata
and
P. sphenops
have masculinized
gestated progenies with undifferentiated gonad but not the gravid females,
in which sex is apparently stably fi xed (Kavumpurath and Pandian, 1992,
1993; George and Pandian, 1995, 1998). Hence
O. nerka, O. mykiss, O. niloticus,
G. affi nis P. reticulata, P. sphenops
and
C. idella
belong to a group, i.e., primary
gonochores, in which sex is stably fi xed by the juvenile stage and their adults
retain unisexual potency only, i.e., the germ cells supporting somatic cells
of the primary gonochores have retained only unisexual potency by the
time they attain the juvenile stage.
On the other hand, the secondary gonochore (see Table 3),
Carassius
auratus,
known for its amenability to hormonally reverse gender in either
direction, regenerates the testis and ovotestis, following ovariectomy.
Clearly, the germ cells supporting somatic cells of secondary gonochores
seem to have retained bisexual potency, like the hermaphrodites, which are
known to have been derived from secondary gonochores.
Yet, it is difficult to reconcile with the report on the failure of
ovariectomized female
O. latipes
and
B. splendens
to regenerate the ovary,
even with E
2
administration. They are known for their amenability to
