Biology Reference
In-Depth Information
process proceeds according to genetic sex determination. Hence the
dimorphic sexual differentiation becomes recognizable prior to hatching, as
in the Japanese medaka fi sh
Oryzias latipes
or after hatching, as in the Nile
tilapia
Oreochromis niloticus
(Fig. 3; see also Fig. 14).
Oncorhynchus kisutch,
Abramis abramis, Esox masquionongy, Sebastes schlegeli, Dicentrarchus labrax
and
Cyprinus carpio
are all good examples for the primary gonochores
(see Devlin and Nagahama, 2002). A variant of the primary gonochores is
the tertiary gonochore in which the bipotential gonad develops directly
into either an ovary or testis (e.g.,
Anguilla anguilla,
Beulbens et al., 1997,
however see also Grandi and Colomba, 1997). Incidentally, the primary
or differentiated gonochores commence with undifferentiated gonad,
whereas undifferentiated or secondary gonochores with gonads that are
already differentiated but non-functional as ovary/ovotestis (see Fig. 3).
Hence the expression of 'differentiated' and 'undifferentiated' gonochores
is a misnomer; they may preferably be named as primary and secondary
gonochores.
Fig. 3.
Ontogenetic pathways of sex differentiation in selected gonochores. Primary gonochores
: A =
Oryzias latipes,
B =
Oreochromis niloticus,
C =
Anguilla anguilla,
Secondary gonochores: D
=
Pterogymnus laniarius
, E =
Mycteroperca rosacea
, F =
Pseudorasbora parva,
G =
Danio rerio
and
H =
Dascyllus fl avicaudus
. OT = Ovotestis, OL = Ovarian lumen, H = Hatching, P = Puberty,
M = Maturation, S = Senescence?
