Biology Reference
In-Depth Information
drawn as an extension of the ovarian cavity, and are extended to form
the oviducts. The testicular cavities are also extended and fused together
to form the outer duct namely the sperm duct. The origin and course of
events in the formation of the gonadal ducts in this protogynic resemble
those in the gonochore like
O. latipes.
During the natural sex change, the
male reproductive passage of the porgy is regressed and degenerated. The
oviduct, arrested as a blunt and during the male phase, is fi nally extended
and connected to the genital pore during the female phase (see also Alam
and Nakamura, 2007).
2.9 Puberty and maturation
Puberty is the transitional period between the immature juvenile stage
and reproductive adult stage, at which an individual begins to produce
the fi rst wave of rapid spermatogonial proliferation or the fi rst batch of
oocytes accumulating cortical alveoli. The two main functions of gonads
are the production of fertile gametes and synthesis of reproductive steroid
hormones, implying functional competence of brain-pituitary-gonad (BPG)
axis. These are convincing evidences that the regulatory input from outside
the gonad is required to trigger pubertal development. Only in captively
reared fi sh, the progressive changes in gonadal histology (e.g., Holland et
al., 2000; Bernet et al., 2009) and endocrine profi le (e.g., Haukenes et al.,
2008) can be followed. Expectedly, this has implications for farmed fi shes.
Taranger et al. (2010) have reviewed the problems and prospects of puberty
in farmed European fi shes. In most fi shes, it is initiated earlier in males
(Table 18), for instance,
Acipenser sinensis
male matures at the age of 14
years, whereas the females by 21 years. Interestingly, Insulin like Growth
Factor (IGF1) is a key somatotropic hormone that conveys growth status
to the reproductive endocrine system. For instance, IGF1 increases steady-
state mRNA levels of
gnrhr1
and four other gonadotropin sub-units
fshb,
chb, cga1
and
cga2,
and may act alone or with GnRH to increase pitiuitary
FSH release in coho salmon
O. kisutsch
one year before puberty, i.e the IGF1
may prime pituitary gonotropic cells of pre-pubertal salmon to respond to
GnRH by stimulating the synthesis of GnRH and FSH at the onset of puberty
(Luckenbach et al., 2010). The onset of puberty is marked by the release of
pituitary-gonadotropin on stimulation by GnRH. Kiss proteins, the peptide
products of the
kiss-1
gene and its receptor (Gpr54) are the gate keepers
of GnRH functions. Extensive studies undertaken on the puberty of the
European sea bass have suggested that
Gnrh1
and its receptor
dlGnrh-II1a
are most relevant for the onset of puberty (Taranger et al., 2010).
Oviparous fi shes can be separated into two groups according to their
spawning strategy. The semelparous species have a single spawning
event during their life time, e.g., salmon (Crespi and Teo, 2002) and a few
