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LA RIPRODUZIONE DEI PESCI:
ASPETTI TEORICI ED
APPLICATIVI
REPRODUCTIVE CYCLE OF TELEOSTS
VARIABILITY OF THE REPRODUCTIVE CYCLE
A majority of teleost fishes are seasonal breeders, while a few breed
continuously.
Among the seasonal breeders, there is wide variation in the time of the
year when breeding occurs.
Fresh water temperate zone fishes spawn in spring and early summer,
while others such as the salmonids do so in autumn.
The time of breeding of each species is so precisely timed that fry are
produced in an environment in which the chances of survival are
maximal.
Natural selection possibly favors genomes of individuals that produce
their young ones at a time most suitable for survival.
REPRODUCTIVE CYCLE PHASES
The reproductive cycle is an ensemble of successive processes from
immature germ cells to the production of mature gametes, with the
final purpose of obtaining a fertilized egg after the insemination with a
spermatozoon.
In both males and females, the reproductive cycle involves two major
phases:
1. the phase of gonadal growth and development (gametogenesis)
2. the phase of maturation, which culminates in ovulation/spermiation
and spawning.
The release of mature gametes to the external environment (spawning)
is a highly synchronized event, leading to fertilization of the egg and
development of the embryo.
The success of reproduction depends on the successful progression
through every process of the reproductive cycle, which leads to the
production of good quality gametes.
Ovarian development: oogenesis, maturation and ovulation
The ovaries are compartmentalized folds (the ovigerous lamellae)
of the germinal epithelium that project transversally to the ovarian
lumen. In the lamellae, the oocytes undergo the various phases of
gametogenesis, until mature ova (i.e., eggs) are released into the
ovarian cavity (cystovarian) or abdominal cavity (gymnovarian) (e.g.,
salmonids) at ovulation and then to the external environment during
spawning.
Ovulated ova may remain in the ovarian/abdominal cavity for a
period of time before spawning. There, they maintain their
maturational competence (fertilizing capacity) for a certain period
of time, but if not spawned, the ova become “over-ripe” through a
process of degeneration.
This is an important consideration in cultured fish whose
reproduction is based on manual egg stripping and artificial
insemination, because stripping should be performed before
over-ripening occurs.
The lapse of time between ovulation and over-ripening varies
greatly among fish, from minutes (e.g., striped bass, Morone
saxatilis) to days (e.g., salmonids) and depends greatly on
water temperature.
In salmonids, which do not have a complete mesovarium and the
oocytes are ovulated directly into the abdominal cavity, the
ovulated ova can remain for several days with no evident overriping.
It initiates with the mitotic proliferation
of the oogonia that undergo primary
oocytes when entering to meiosis.
The primary oocytes go through a primary growth phase
(pre-vitellogenesis), which involves the appearance of
pale material in the cytoplasm and formation of the two
layers of surrounding granulosa and theca cells (i.e.,
follicular wall).
The secondary growth phase (vitellogenesis) involves
the synthesis and incorporation into the oocyte of
vitellogenin (VTG), and is associated with a drastic
increase in size. During vitellogenesis, new inclusions
appear in the cytoplasm, such as the cortical alveoli
(white circles), lipid globules (light grey circles) and
yolk granules (dark grey circles) and the oocyte wall
(i.e., zona radiata) and follicular wall become
increasingly thick.
At the end of vitellogenesis, the cytoplasm is filled
completely with lipid globules and yolk granules at the
onset of coalescence, the nucleus (germinal vesicle, GV)
(black circle) is centrally located and a thick zona
radiata surrounds the oocyte.
At early maturation, lipid globules and yolk granules continue
coalescence and the nucleus migrates to the animal pole (GV
migration, GVM). As maturation advances, there is a massive
coalescence of yolk granules and localization of the nucleus at a
peripheral position.
Hydration: relevant in
fishes producing
pelagic eggs
Final oocyte maturation (FOM) is characterized by
the dissolution of the GV membrane (GV break
down, GVBD) and hydration of the oocyte.
Oocytes are finally ovulated into the ovarian or
abdominal cavity, and are released in the water
during spawning.
Assessment of the Stage of gonadal development
The determination of the stage of gonadal development in female breeders is an
important tool in aquaculture.
This can be determined by examination of biopsies of oocyte samples.
The biopsy is performed in anesthetized females, by insertion of a cannula through
the gonoduct and gentle aspiration of intra ovarian oocytes.
The collected oocytes are observed under the binocular and classified according to
their size, position of the GV (central, migrating or peripheral), degree of yolk
granule coalescence, etc.; these classifications give a relative indication of the
stage of gonad development of the females.
Progression of oocyte development
from primary growth oocytes (PG), to secondary growth, which begins with
the cortical alveolar (CA) stage and then proceeds through vitellogenesis
(Vtg), which can be broken into substages associated with the extent of
yolk globules or platelets in the ooplasm (primary [Vtg1], secondary [Vtg2],
and tertiary [Vtg3]). Oocyte maturation (OM) occurs after the appropriate
trigger and can include germinal vesicle migration (GVM), yolk coalescence
(YC), germinal vesicle breakdown (GVBD), and in pelagic spawners, hydration
(H). At ovulation, the follicle ruptures and the oocyte is released.
Postovulatory follicles (POF) remain in the ovary, where they are resorbed.
An oocyte surrounded by two
layers of follicular cells that
offer structural and functional
support to the developing
oocyte, mediating the
internalization of external
molecules, synthesizing
hormones and factors
necessary for the
differentiation, growth and
survival of the oocyte.
Each oocyte is surrounded by an
inner mono-layer of granulosa cells
and an outer mono-layer of theca
cells. Between the two follicular
layers there is a thin basal
membrane. Also, a thick acellular
envelop surrounds the oocyte (zona
pellucida). Granulosa cells microvilli
and oocyte microvilli cross the zona
pellucida, changing its name in zona
radiata.The zona radiata develops
progressively during gametogenesis,
becoming increasingly thick and
compact to constitute the egg
chorion or egg shell.
Testicular development in males: spermatogenesis,
maturation and spermiation
In Teleosts, testes can be either tubular or lobular. In tubular testes
the ends of the tubules hooks the efferent ducts, forming loops, while
the lobular testes have blind ends.
Within the wall of the tubules there are germinal cells at different
stages of maturity.
In the lobular testis there are cysts with germ cells at the same stage
of maturation. Spermatozoa containing cysts can either open up and
release spermatozoa in the lumen of the lobule (unrestricted testis), or
can move up to the end of the lobule and release the spermatozoa near
its end (restricted testis).
After
Mari Carmen Uribe, Harry J Grier and Víctor Mejía-Roa (2014)
Comparative testicular structure and spermatogenesis in bony fishes.
Spermatogenesis. 4(3): e983400.
Tubular testis
This testis type is present in lower fishes, as salmonids, cyprinids and
lepisosteids
Unrestricted lobular testis
This testis type is found in neoteleosts, except for the atherinomorphs.
Restricted lobular testis of the poeciliid Poecilia latipinna
This testis type is found
in all Atherinomorpha
(Atheriniformes,
Beloniformes and
Cyprinodontiformes).
The restriction of
spermatogonia to the
termini of the lobules
supports the monophyly
of that group.
Sertoli stem cells?
Sperm stem cells
Spermiation
Elongating
spermatogonia
Spermatogonia
Round spermatids
Spermatocytes
Schematic drawing of cystic spermatogenesis observed in fish and amphibians.
In anamniote testes, a cyst of Sertoli cells surrounds each germ cell syncytium. Sertoli cells
share their fate with the developing germ cell syncytium that they nourish, and eventually
degrade when germ cells mature and spermiate.
Tight junctions are established between Sertoli cells that cover haploid spermatids and
more advanced germ cells.
The spatial organization of cysts within the testis varies highly between species. They are
aligned in the order of development in some fish, while others do not have such a polarized
organization.
Siti web su cui trovare info relative al teleosteo e diffuso
modello animale
zebrafish
https://en.wikibooks.org/wiki/The_Zebrafish_in_Toxicology/Spermatogenesis
http://zfishtoxpat.comoj.com/tesdet.html#
Types of gonadal development
The ovarian development can be classified in three major types:
• synchronous exhibited by those species spawning only once in their life (freshwater
eel (Anguilla spp), and Pacific salmons (Oncorhynchus spp). In this type of ovary, all
oocytes advance in synchrony through all phases of gametogenesis.Thus, only one type of
developing oocyte class is present in the ovary.
• group-synchronous
exhibited by the seasonal spawners, those species that spawn
one or more times during the annual reproductive season. In this type, a cluster of
vitellogenic oocytes is recruited and advance synchronously through further stages of
development, whereas the rest of the oocyte population remains arrested. The cluster
of recruited oocytes will undergo maturation, ovulation and spawning. This type of
ovarian development can be divided in two subgroups: single-batch and multiple-batch
spawners. In the single-batch group synchronous species, only one batch of oocytes
undergoes maturation every season and thus, they produce one single spawn per year
(e.g., rainbow trout, Oncorhynchus mykiss). The multiple-batch group synchronous
species are able to repeat this process several times during the spawning season, with
the recruitment of successive batches of oocytes and thus the production of several
spawns per year. The number of spawning depends on the number of recruitments, e.g.,
the European sea bass (Dicentrarchus labrax) producing 2-4 spawns per season.
• Asynchronous is exhibited by those species that produce multiple spawns through
an expanded period of time (several months), normally on a daily basis. This is typical of
some tropical species and in the Mediterranean sea the Sparus auratus (orata)
The testis development
The development of the testes is more homogenous and could be
described as an asynchronous type of development for all species.
Male fish used to be fluent on a daily basis through a long period of
time, normally overlapping the spawning period of the females. At every
moment, several classes of cell development, from immature
spermatogonia to spermatozoa, can be found in the testes. At the full
spermiation period, the testes are mostly occupied by mature
spermatozoa, ready for spermiation, while early in the season, a high
percentage of less mature spermatocytes is present.
ENVIRONMENTAL REGULATION OF FISH
REPRODUCTION
Factors that determine survival and reproduction:
Food availability and environmental conditions
Fish have the ability, through a genetically determined bio-chemical
threshold, to ascertain what size and/or age conditions are optimal to
complete maturation both during the first and subsequent maturation
episodes.
Food availability for offspring and hence off-spring survival
determines the timing of reproduction
Photoperiod, temperature,
lunar cycles, weather cycles
and ocean currents, control
the seasonality
of food availability and
entrain maturational
development of fish.
Food availability and the
ability
to store energy determine
when a fish attains a
genetical threshold and
proceeds to the completion
of maturation.
Maturational development
of the fish is entrained by
environmental factors to
ensure that critical offspring feeding periods
coincide with peaks in food
availability which are
months or years after
maturation is initiated.
Perhaps the most important proximate factor is photoperiod.
photoperiod controls all aspects of maturational development, i.e., the entire
brain-pituitary-gonad axis.
In the rainbow trout:
1. the increasing spring photoperiod entrains the start of
vitellogenesis/spermatogenesis,
2. the passage of photoperiod from spring to summer to autumn entrains the
progress of vitellogenesis/spermatogenesis,
3. the decreasing autumn photoperiod entrains final maturation, ovulation and
spermiation.
Photoperiod plays an important role in the timing of reproduction of most
temperate fish species such as the Atlantic salmon (Salmo salar, family:
Salmonidae), European seabass (Dicentrarchus labrax, Percichthyidae), gilthead
bream, (Sparus aurata, Sparidae), Atlantic cod (Gadus morhua, Gadidae),
Atlantic halibut, (Hippoglossus hippoglossus, Pleuronectidae), sole (Solea solea,
Soleidae), and tropical latitudes, such as the Nile tilapia (Oreochromus
niloticus), grey mullet (Mugil cephalus, Mugilidae), catfish (Heteropneustes
fossilis, Heteropneustidae)and common carp (Cyprinus carpio, Cyprinidae)
HORMONAL REGULATION OF FISH REPRODUCTION
The reproductive cycle is regulated by a cascade of hormones along
the brain-pituitary-gonad (BPG) axis, the so-called reproductive
axis
The pituitary gland of teleosts
1.
At initial stages
GTH stimulation (mainly FSH) induces the secretion of androgens
(testosterone and 11-ketotestosterone ) in males and estrogens (estradiol ) in
females, which act concomitantly with FSH in the control of gametogenesis.
The E2 plays an additional important role in female gametogenesis, with the
stimulation of VTG synthesis from the liver.
2.
At the end of gametogenesis
Secretion of LH from the pituitary induces a shift in the steroidogenic
pathway of the gonad, stimulating the synthesis and secretion of progestin-like
steroids, the maturation-inducing steroids (MIS). The concomitant action of
LH with the MIS stimulates the process of gonadal maturation. This period is
characterized by decreasing blood levels of FSH and androgens/estrogens and
increasing blood levels of LH and MIS. Once gonadal maturation is completed,
the brain GnRH system stimulates a high surge of LH secretion from the
pituitary, which induces ovulation in the females, whereas in the males,
relatively stable but elevated levels of LH induce spermiation.
The GnRH-induced pre-ovulatory LH surge in the plasma is essential for
successful ovulation. In fact, the demonstration that this characteristic LH
surge was absent in captive fish that failed to ovulate, but not in wild fish
ovulating spontaneously, set up the basis for the development of hormone
based spawning induction therapies in aquaculture. The stress associated with
captivity or the absence of appropriate environmental conditions in culture
facilities may act on the brain-inhibiting neuroendocrine secretions.
At initial stages, pituitary FSH
stimulation induces gonadal
secretion of E2 in females and
androgens in males (11KT)that
regulate gonad
development. In females, E2
plays an additional role on the
liver, stimulating VTG synthesis.
The period of gametogenesis is
characterized by high blood
levels of FSH and
increasing levels of androgens in
males, and E2 and VTG in
females.
At the end of gametogenesis,
pituitary LH secretion induces
the synthesis of maturationinducing steroids (MIS), which
regulate the process of gonadal
maturation; this period is
characterized by decreasing
blood levels of FSH and
androgens/estrogens and
increasing blood levels of LH
and MIS.
At completion of maturation, a
GnRH induced LH surge
stimulates ovulation,
spermiation and spawning.
Brain Gonadotropin-Releasing Hormone (GnRH)
The stimulatory action of GnRH on GTH secretion is dependent on the
presence of GnRH receptors (GnRH-R) in the membrane of the pituitary
gonadotrops.
In fish, multiple GnRH-Rs have been identified and, in contrast to mammals,
they do not show ligand specificity.
Expression levels of the GnRH-R genes in the pituitary show a seasonal pattern,
which is an important factor influencing the seasonal responsiveness of the
pituitary to GnRH stimulation. Highest levels of GnRH-R and thus highest
responsiveness of the pituitary occur at the pre-spawning period, whereas
lowest GnRH-R levels are found during the resting period and early stages of
gonadal development. This is critical not only for the natural development of
the reproductive cycle, but also when applying hormonal therapies, as this
affects greatly the efficiency of GnRHa-based hormonal treatments,
depending on the moment of the cycle when the treatments are applied.
In addition to the primary GnRH stimulatory system, GTH
secretion is under the influence of a brain inhibitory tone, the
dopaminergic system
Neurons secreting dopamine (DA) exert an inhibitory action on both the brain and
pituitary.
DA effects:
•
InhibitsGnRH synthesis and GnRH release in the brain;
•
Down-regulates GnRH-R in the pituitary;
•
Interferes with the GnRH signal-transduction pathways, inhibiting GnRHstimulated LH secretion from the pituitary.
In many freshwater species, DA inhibits strongly the pre-ovulatory GnRH-stimulated
LH surge and thus, ovulation and spawning. In contrast, an active DA inhibitory
system seems to be very weak or absent in most marine fishes.
La dopammina (o dopamina) è un neurotrasmettitore endogeno della famiglia
delle catecolammine. All'interno del cervello questa feniletilammina funziona
da neurotrasmettitore, tramite l'attivazione dei recettori dopamminicispecifici e subrecettori.
La dopammina è prodotta in diverse aree del cervello, tra cui la substantia nigra e l'area
tegmentale ventrale (ATV). Grandi quantità si trovano nei gangli della base, soprattutto
nel telencefalo, nell'accumbens, nel tubercolo olfattorio, nel nucleo centrale dell'amigdala,
nell'eminenza mediana e in alcune zone della corteccia frontale.
Nessun altro sistema neuronale ha ricevuto tanta attenzione negli ultimi 20 anni quanto quello
dopamminergico. La dopammina è anche un neuro ormone rilasciato dall'ipotalamo. La sua
principale funzione come ormone è quella di inibire il rilascio di prolattina da parte del lobo
anteriore dell'ipofisi. A livello gastrointestinale il suo effetto principale è l'emesi.
La dopammina può essere fornita come un farmaco che agisce sul sistema nervoso simpatico,
producendo effetti come aumento della frequenza cardiaca e pressione del sangue.
Ha formula chimica C6H3(OH)2-CH2-CH2-NH2. Il suo nome chimico è 4-(2amminoetil)benzene-1,2-diolo e la sua sigla è "DA". Fa parte della famiglia catecolammine (un
anello benzenico con due gruppi ossidrilici), al quale poi è legato un gruppo etilamminico. La
dopammina è un precursore della noradrenalina e dell'adrenalina.
Although GnRH is the primary regulator of reproduction, the
brain synthesizes other neurohormones and neurotransmitters
that have been shown to stimulate LH secretion and participate
in the regulation of fish reproduction
The NPY is involved in the regulation of the nutritional status of the fish.
NPY neurons exert stimulatory actions on both GnRH and GTH and seem to play
an important role in mediating interrelationships between nutrition and
reproduction.
The neurotransmitter γ-amino-butiric acid (GABA). The GABA is the
most relevant neurotransmitter of the brain; in mammals and in fish
it exerts a stimulatory action over LH secretion.
Il neuropeptide Y (NPY) è un polipeptide molto diffuso nel sistema nervoso
centrale e nel sistema nervoso autonomo; svolge diverse azioni, tra cui l'aumento
dell'appetito e la modulazione della risposta vasocostrittrice innescata
dai neuroni noradrenergici.
Il neuropeptide Y fa parte delle famiglia che comprende il peptide YY e
il polipeptide pancreatico. È formato da 36 aminoacidi:
-OOC-Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gli-Glu-Asp-Ala-Glu-Asp-
-Met-Ala-Arg-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-GlnArg-Tyr-NH2
Funzioni nel sistema nervoso centrale
Il neuropeptide Y è un potente stimolatore dell'appetito ed ha uno spiccato
effetto oressizzante. Nel Sistema Nervoso Centrale, sia degli uomini che degli
animali, è stato dimostrato il ruolo del NPY sia come ansiolitico (composto in
grado di combattere i sintomi dell'ansia al pari dei classici farmaci) che anti
depressivo. Questo neuropeptide è inoltre coinvolto nel consumo e abuso di
alcolici, infatti le persone che soffrono di depressione e gli alcolisti hanno livelli
alterati di questo neuropeptide nell'organismo. La localizzazione di NPY
nell'ippocampo lo rende importante nei processi di apprendimento e memoria; in
questa regione del cervello è inoltre capace di stimolare la proliferazione neuronale
e ciò è in accordo con le sue proprietà antidepressive.
GABA (sigla di GammaAmminoButirrico Acido) Neurotrasmettitore di tipo
inibitorio, il più importante del sistema nervoso centrale; è prodotto a partire
dall’acido glutammico, per decarbossilazione catalizzata dell’enzima
glutammicodecarbossilasi.
Il GABA è ampiamente diffuso nel cervello e nel midollo spinale. Sono stati
identificati diversi recettori postsinaptici per l’acido γ-amminobutirrico: i
recettori GABAA e GABAC (questi ultimi presenti solo nella retina) sono di tipo
ionotropico e controllano un canale di membrana specifico per il cloro; il
recettore GABAB è, invece, di tipo metabotropico accoppiato a proteine G e
controlla un canale per il potassio. I recettori GABAA sono il bersaglio di
farmaci ansiolitici e ipnotici (le benzodiazepine e i barbiturici) o antiepilettici
(l’acido valproico), che agiscono sul sistema nervoso potenziando il sistema
GABAergico (cioè il sistema costituito dai neuroni che utilizzano il GABA).
Pituitary Gonadotropins (GTH)
The two pituitary GTHs, FSH and LH, together with the placental chorionic
gonadotropin (CG) are glycoprotein hormones. They are heterodimeric proteins,
constituted by a common α subunit, noncovalently linked to a hormone-specific β
subunit, which confers the biological specificity to the hormone
The half-life of the GTHs in the bloodstream is determined mainly by its degree of
glycosilation. Human CG (hCG) is used in the spawning induction protocols in fish since
it is the highest glycosilated GTH and thus, it presents higher resistance to
degradation than any other glycoprotein.
The general view is that:
FSH controls mainly early stages of gametogenesis,
LH regulates FOM, ovulation and spermiation.
There are important differences between fish species, most
probably related to different patterns of gonadal development
and different reproductive strategies.
The initiation of the reproductive cycle is characterized by increased FSH
levels, which are maintained high during gametogenesis, whereas LH levels
remain undetectable. During gonadal maturation, FSH levels decline and LH
increase, showing a sharp LH peak prior to ovulation.
In salmonid species, showing single-batch group synchronous ovarian
development, FSH increase during early gametogenesis while LH
predominates during FOM.
Nonsalmonid species show a slightly different picture. In the gilthead
seabream (Sparus aurata), with asynchronous ovarian development, both
FSH and LH are expressed throughout the year, increasing both during the
reproductive season .
In other nonsalmonid species, exhibiting multiple-batch group synchronous
or asynchronous ovarian development, such as the blue gourami
(Trichogaster trichopterus), red seabream (Pagrus major), European
seabass (Dicentrarchus labrax) and stickleback (Gasterosteus aculeatus),
FSH and LH levels are found throughout the reproductive cycle, although in
most cases FSH synthesis is advanced with respect to that of LH.
Gonad steroids
Steroidogenesis takes place in the somatic cells of the gonad,
the granulosa and theca cells in the ovary and the interstitial
Leydig cells and Sertoli cells in the testes.
The major steroid hormones in the regulation of fish
gametogenesis are the estrogen E2 in females and the androgen
11KT in males and, to a lower extent, dihydrotestosterone
(DHT).
The fish ovary also synthesizes T, which plays other
reproductive related functions. Similarly, males also synthesize
E2, but this is found in much lower levels than in females. The
testes of male fish produce other androgens than 11KT (DHT,
T), which exert complementary functions during testicular
development.
Gonadal steroids effects
•
•
•
•
•
Regulation of gonadal development.
Both positive and negative feedback on the brain-pituitary axis and thus,
Regulation of GTH release.
A major positive action of the steroids is to enhance pituitary responsiveness to
GnRH, probably by stimulating GnRH-R.
A major negative action of these steroid hormones is exerted through the
dopaminergic system, increasing DA turnover and thus enhancing the DA
inhibitory tone over GTH secretion.
In this way, the brain is constantly informed about the evolution of gonad
development, through the action of the fluctuating circulating levels of steroids
during the reproductive cycle.
Steroids regulate female oogenesis and maturation
At the end of the vitellogenic stage…
Pituitary LH secretion induces a shift in the steroid biosynthetic activity of the
ovary with a reduction in T and E2 production and enhancement of the synthesis
of MIS. This is caused by reduction of aromatase activity and increased
activity of enzymes of the MIS pathway.
There are two major MIS identified in fish:
1. 17α,20β,dihydroxy-4-pregnen-3-one (17,20β-P)
2. 17α,20β,21-trihydroxy-4-pregnen-3-one (20β-S).
They both probably act as MIS in most fishes, but normally one of them is the
predominant MIS for a given species.
The 17,20β-P is the major MIS in several salmonid and nonsalmonid species,
while 20β-S is the major MIS in Atlantic croaker, spotted sea trout, striped
bass and black porgy.
The synthesis of MIS is also a two-cell process, by which the precursor 17βhydroxyprogesterone is synthesized in theca cells and converted into 17,20β-P
in the granulosa cells, by the enzyme 20β-hydosysteroid dehydrogenase.
Steroids regulating male spermatogenesis and maturation
The LH is mainly involved in the stimulation of androgen production in Leydig
cells.
FSH stimulates 11KT production in Leydig cells through activation of specific
enzymes (11α-hydroxylase and 11α-hydroxysteroid dehydrogenase) and
regulates Sertoli cell activity during spermatogenesis.
11KT regulates the full process of spermatogenesis.
FSH levels are high at early spermatogenesis, increase to maximum levels
during the rapid testicular growth phase and then decline after spawning. On
the other hand, LH is very low during early spermatogenesis, start increasing
during the rapid testicular growth phase and peaks during spawning. As
spermatogenesis advances, LH becomes important in supporting 11KT
production. After completion of spermatogenesis, secretion of LH from the
pituitary induces a shift in the steroidogenic pathway of the testes leading to
the production of MIS, which in turn regulate sperm maturation.