Rodríguez_etal_2001(Gonadotropin-Sexual-steroids-Puberty-Photoperiod-Sea-bass).pdf

Ž .
Aquaculture 202 2001 235–248
www.elsevier.comrlocateraqua-online
Changes in plasma levels of reproductive hormones
during first sexual maturation in European male
ž /
sea bass Dicentrarchus labrax L. under
artificial day lengths
Lucinda Rodrıguez, Ideal Begtashi, Silvia Zanuy,
´
Monica Shaw, Manuel Carrillo)
´
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Consejo Superior de InÕestigaciones Cientıficas CSIC , Instituto de Acuicultura de Torre la Sal,
´
12595 Ribera de Cabanes, Castellon, Spain
´
Abstract
Photoperiod has been considered one of the most important factors triggering puberty, as well
Ž .
as reproduction, in several fish species, including sea bass Dicentrarchus labrax L. . In the
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present work, the effect of expanded EX and compressed CO photoperiods on plasma levels of
Ž Ž . Ž . Ž
reproductive hormones gonadotropin-2 GTH-2 , testosterone T and 11-ketotestosterone 11-
.. Ž Ž ..
KT and gonadal maturation spermiation time and gonadosomatic index GSI were investigated
Ž .
in male sea bass during the first sexual maturation October to April . Spermiation in controls was
apparent from December to February–March. In EX and CO groups, spermiation was advanced
by 2 months, although the CO group displayed a bimodal pattern, and testicular growth in both
experimental groups was significantly reduced with respect to the controls. Plasma GTH-2 levels
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in controls showed the highest value ;30 ngrml in the middle of the spermiation period, while
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EX group displayed the maximum level 4 months earlier 35"2.7 ngrml than controls. The CO
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group presented two peaks, the first of which 15.16"5.20 ngrml was advanced by 3 months
with respect to the control peak. T and 11-KT levels in the control displayed the highest values
during the spermiation period. The EX group showed lower T levels than controls, but both
peaked at the same time. However, 11-KT levels remained low and unchanged. The CO group
displayed two significant increases in T levels accordingly with the spermiation pattern, while the
11-KT profile only exhibited a significant increase 2 months earlier than in controls. Results
obtained indicated an involvement of GTH-2 in gonadal maturation. In addition, T is suggested to
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be involved in the activation of the brain–pituitary–gonad BPG axis during pubertal develop-
)
Corresponding author. Tel.: q
34-64-319-500; fax: q
34-64-319-509.
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E-mail address: carrillo@iats.csic.es M. Carrillo .
0044-8486r01r$ - see front matter q2001 Elsevier Science B.V. All rights reserved.
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PII: S0044-8486 01 00774-8

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L. Rodrıguez et al.rAquaculture 202 2001 235–248
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236
ment, while 11-KT may act by stimulating spermatogenesis andror spermiation in juvenile male
sea bass. Furthermore, the profiles of these reproductive hormones were altered by both expanded
and compressed photoperiods, and first sexual maturation was advanced by at least 2 months.
q 2001 Elsevier Science B.V. All rights reserved.
Keywords: Gonadotropin; Sexual steroids; Puberty; Photoperiod; Sea bass
1. Introduction
The processes covering the transition from an immature juvenile to a mature adult
reproductive system, and the associated endocrine changes that precede it, can be
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defined as puberty Schulz and Goos, 1999 . This period is completed with the first
spawning season. In males, puberty starts with the appearance of spermatocytes and
Ž
ends with the presence of the first spermatozoa in the adolescent fish Cavaco et al.,
. Ž Ž .
1998 , followed by an increment in serum levels of androgens i.e., testosterone T and
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11-ketotestosterone 11-KT Rodrıguez et al., 2000a . The sea bass Dicentrarchus
´
.
labrax L. is a gonochoristic species in which males attain first sexual maturity at 2
years of age. Related studies in fish have demonstrated the involvement of the
Ž . Ž
brain–pituitary–gonad BPG axis in the control of the onset of puberty Schulz and
.
Goos, 1999 . However, it still remains unclear which specific factors affect the
development of the BPG axis in fish. Sex steroids are known to influence the pituitary
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and the brain Schulz and Goos, 1999 , being involved in the timing of activation of the
BPG axis, and in the endocrine events leading to the onset of puberty. A positive
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feedback of gonadal steroids on gonadotropin-2 GTH-2 synthesis in prepuberal
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animals by treatment with aromatizable androgens T has been reported Gur et al.,
. Ž .
1995; Pavlic and Moberg, 1997; Holland et al., 1998 . Similarly, Zanuy et al. 1999
have demonstrated that T implants increase pituitary GnRH levels and advance puberty
in prepuberal sea bass.
External factors, such as photoperiod andror temperature, are known to be activators
andror timers of the BPG axis being involved in the regulation of puberty. Studies on
the relationship between the environmental factors and the onset of puberty in fish are
Ž . Ž
limited to the rainbow trout Oncorhynchus mykiss; Bromage, 1987 , masu salmon O.
. Ž
masou; Amano et al., 1994, 1995 , chinook salmon O. tsawytacha; Clarke and
. Ž .
Blackburn, 1994 , Atlantic salmon Salmo salar; Oppedal et al., 1997 , turbot
Ž . Ž
Scophthalmus maximus; Imsland et al., 1997 and, recently, sea bass Rodrıguez et al.,
´
.
2001 . It has been reported that fish exposed to compressed photoperiod can advance
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spawning time Carrillo et al., 1993 . In addition, expanded photoperiods advance the
onset of puberty in prepuberal male sea bass but reduce gonad size and rates of
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spermiation Rodrıguez et al., 2001 . However, there is a lack of information on the
´
effects of accelerated photoperiods on the profiles of reproductive hormones during the
first sexual maturation in the sea bass, particularly, when these photoperiods are applied
from early developmental stages.
The aim of the present work was to elucidate the effect of expanded and compressed
photoperiods on plasma GTH-2, T and 11-KT profiles and to correlate these fluctuations

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´ 237
Ž Ž ..
to changes in testicular maturation spermiation time and gonadosomatic index GSI in
juvenile male sea bass during the first sexual maturation.
2. Materials and methods
2.1. Fish and rearing conditions
Two separate experiments were performed at the Instituto de Acuicultura de Torre la
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Sal Castellon, Spain . Both experiments began in June when the natural day length was
´
approximately 15-h lightr9-h dark.
2.1.1. Experiment I
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Two thousand 4-month-old sea bass were purchased from GESA Gas y Electricidad,
.
Islas Baleares, Spain . Fish were distributed in two groups and held in duplicated in
separate identical 2000-l flow-through circular fibre-glass tanks, supplied with well-
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aerated seawater salinitys37‰ , during two consecutive years 1995 to 1997 .
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Temperature was always under natural conditions 12.0"1.0 to 26.3"1.0 8C Fig. 1 .
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One group, which served as control NP1 , was exposed to the natural photoperiod
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408N; 08E , and the other group was exposed to an expanded photoperiod 18 months;
.
EX . Fish were fed by hand ad libitum three times a day with pelleted dry food of the
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appropriate size Inve Aquaculture, Baasrode, Belgium; Ewos, Madrid, Spain .
2.1.2. Experiment II
Six hundred 5-month-old sea bass were purchased from GESA. Fish were distributed
in two groups and held in duplicate in separate identical 500-l fibre-glass tanks, in the
same conditions, including density, as in Experiment I, during two consecutive years
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1996 to 1998 . Temperature was always under natural conditions 12.0"1.0 to
. Ž . Ž .
26.1"1.0 8C Fig. 1 . One group, which served as control NP2 , was exposed to
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natural photoperiod 408N; 08E , and the other group was exposed to a compressed
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photoperiod 6 months; CO . Fish were fed in the same way as those from Experiment I.
2.2. Sampling
Fish from every tank were sampled monthly and males were gently stripped at each
sampling time in order to determine the number of spermiating males. Fish from
Experiment I were sampled until February 1997 since they fell ill in March 1997.
Around 20–30 fish per tank were anaesthetised per sampling, weighed, bled and
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sacrificed. Plasma was obtained by centrifugation 48C for 20 min at 2500=g and
stored at y80 8C. Gonads were quickly removed and weighed for the calculation of the
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gonadosomatic index GSI .
2.3. GTH-2 immunoassay
GTH-2 plasma levels were determined by an heterologous ELISA developed for
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striped bass Mananos et al., 1997 and validated for its use in sea bass, using striped
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238
Fig. 1. Experimental design of the temperature cycle and photoperiod regimes used. The horizontal grey bars
indicate the time when spermiation took place in each treatment. NP1 and NP2snatural photoperiods for
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Experiments I and II, respectively; EXsexpanded photoperiod 18 months ; COscompressed photoperiod
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6 months .
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bass stb GTH-2b subunit antibodies and intact stbGTH-2 for the standard curve. The
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sensitivity of the assay was around 0.156 ngrml BirBos90% and half-displacement
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occurred at around 2.5 ngrml BirBos50% . The intra-and interassay coefficients of
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variation CV were 6% and 7%, respectively ns21 .

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2.4. Steroid assays
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T plasma levels were determined by specific immunoassay EIA developed by
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Rodrıguez et al. 2000b for sea bass. 11-KT plasma levels were analysed using an EIA
´
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developed for the Siberian sturgeon Cuisset et al., 1994 and modified for its use in sea
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bass. The protocol was similar to that described by Cuisset et al. 1994 except that
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primary antibodies were used at a final dilution of 1:320,000 and the tracer Cayman
. Ž .
Chemicals, MI, USA was diluted at 1:10 Ellman Units EU rml. The ratio between
11-KT and T levels was determined for both experiments by dividing the 11-KT value
Ž . Ž .
in ngrml by the T value in ngrml every month during the entire period.
2.5. Statistical analyses
Percentage data were subjected to an arcsin transformation prior to statistical
analysis. Data were analysed using a one-way ANOVA followed by a Fisher’s multiple
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range tests. Data that were not normal or did not have equal variance Bartlett’s test
were transformed or subjected to a Kruskal–Wallis on ranks nonparametric test.
Significant differences were accepted when P-0.05. The results were expressed as the
mean"standard error.
3. Results
3.1. Spermiation and GSI
3.1.1. Experiment I
Spermiation in the NP1 group started in November, although the maximum percent-
ages of spermiating males were in December, January and February, respectively
Ž . Ž . Ž .
P-0.05 Fig. 2A . GSI followed the same pattern Fig. 2A . The highest percentage
of spermiating males was first observed in October in EX group, decreasing during the
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next months until 0% in January and February Fig. 2A . GSI presented the highest
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value in November, decreasing onwards Fig. 2A .
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The first spermiating males appeared in November in NP2 group Fig. 2B . There
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was an increase in December that lasted until March, decreasing in April P-0.05 .
GSI presented the same evolution, with the highest values coinciding with the maximum
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percentage of spermiating males Fig. 2B . The pattern of spermiation in CO group was
bimodal. The first increase in spermiating males was observed in October–November
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P-0.05 and the second one was in March–April P-0.05 . Two peaks were
displayed in GSI for CO group, concomitant with increases in spermiating males
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Fig. 2B .

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240
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Fig. 2. Percentage of spermiating males black bars and gonadosomatic index GSI; dotted lines for male sea
Ž . Ž .
bass of Experiment I A and Experiment II B during the first sexual maturation. NP1 and NP2snatural
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photoperiods for Experiments I and II, respectively; EXsexpanded photoperiod 18 months ; COs
Ž . Ž .
compressed photoperiod 6 months . Different letters indicate significant differences P-0.05 . Lower case
letters indicate differences between months in the same group and upper case letters indicate differences
between groups in the same month.

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3.2. Plasma GTH-2 leÕels
3.2.1. Experiment I
Plasma GTH-2 levels in NP1 group remained low during the early phases of pubertal
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development October–November , displaying the first significant increase in December
Ž . Ž . Ž .
P-0.05 to peak in February ;30 ngrml Fig. 3A . The highest value in the EX
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Fig. 3. Plasma GTH-2 levels in male sea bass during the first sexual maturation. A Experiment I: natural
Ž . Ž . Ž . Ž .
photoperiod NP1 and expanded photoperiod EX, 18 months ; B Experiment II: natural photoperiod NP2
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and compressed photoperiod CO, 6 months . Horizontal bars on the X-axis represents the spermiation period
Ž . Ž .
for NP1 and NP2 groups grey bars and EX and CO groups dark grey bars . Different letters indicate
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significant differences P-0.05 . Lower case letters indicate differences between months in the same group
and upper case letters indicate differences between groups in the same month.

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242
Ž .
group was observed in October P-0.05 , decreasing in November to remain low
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thorough the rest of the period Fig. 3A .
Plasma GTH-2 levels were unchanged in NP2 group from October to January,
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peaking in February to decrease until minimum values in March Fig. 3B . There was a
bimodal pattern in CO group, with a peak in November and a second peak in February
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Fig. 3B .
Ž . Ž .
Fig. 4. Plasma testosterone left graphs and 11-ketotestosterone right graphs levels for male sea bass of
Ž . Ž .
Experiment I A and Experiment II B during first sexual maturation. NP1 and NP2snatural photoperiods
Ž .
for Experiments I and II, respectively; EXsexpanded photoperiod 18 months ; COscompressed photope-
Ž .
riod 6 months . Horizontal bars on the X-axis represents the spermiation period for NP1 and NP2 groups
Ž . Ž .
grey bars and EX and CO groups dark grey bars . Different letters indicate significant differences
Ž .
P-0.05 . Lower case letters indicate differences between months in the same group and upper case letters
indicate differences between groups in the same month.

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3.3. Plasma T and 11-KT leÕels
3.3.1. Experiment I
Plasma T levels in NP1 group showed the first significant increase in November,
Ž . Ž .
attaining the highest values in December and January P-0.05 Fig. 4A . A dramatic
Ž . Ž .
Fig. 5. Relation between 11-ketotestosterone 11-KT and testosterone T levels for male sea bass of
Ž . Ž .
Experiment I A and Experiment II B during first sexual maturation. NP1 and NP2snatural photoperiods
Ž .
for Experiments I and II, respectively; EXsexpanded photoperiod 18 months ; COscompressed photope-
Ž .
riod 6 months . Horizontal bars on the X-axis represents the spermiation period for NP1 and NP2 groups
Ž . Ž .
grey bars and EX and CO groups dark grey bars . Different letters indicate significant differences
Ž .
P-0.05 . Lower case letters indicate differences between months in the same group and upper case letters
indicate differences between groups in the same month.

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244
Ž .
decrease was observed in February P-0.05 . In the EX group, T levels were
significantly lower that those of NP1 group during the most part of the period,
Ž .
displaying a small peak in December P-0.05 and elevated levels in the following
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months Fig. 4A . The 11-KT plasma levels in NP1 group followed the same pattern as
T but were twofold higher, while 11-KT plasma levels in EX group remained very low
Ž .
and were unchanged during all the period Fig. 4A .
Plasma T levels in the NP2 group displayed the highest values between November
Ž .
and January Fig. 4B . In the CO group, two peaks in T levels appeared: one in October
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and another in January Fig. 4B . The pattern of 11-KT plasma levels in the NP2 group
was similar as that of T but peaking between December and February. Only one peak
appeared in the CO group in October–November, decreasing in December to remain
Ž .
very low during the following months Fig. 4B .
3.4. Ratio 11-KTrT
3.4.1. Experiment I
The ratio 11-KTrT showed the highest values in December, January and February in
NP1 group, while the pattern was inverted in the EX group, displaying the highest value
Ž . Ž .
in October P-0.05 and low levels from November to February Fig. 5A .
The ratio between 11-KT and T levels in the NP2 group followed the same pattern
Ž .
than that of NP1 group, decreasing until 0 in March Fig. 5B . In the CO group, the ratio
11-KTrT presented a significant increase in November and remained low and un-
Ž .
changed during the rest of the period Fig. 5B .
4. Discussion
In the present work, plasma levels of GTH-2, T and 11-KT were determined during
the first sexual maturation in pre-pubertal sea bass exposed to expanded and compressed
photoperiods. The GTH-2 profile obtained in all groups, irrespective of the photoperiod
treatment, suggests an important role of this hormone in testicular maturation. Elevated
GTH-2 plasma levels were maintained throughout the spermiation period, indicating that
GTH-2 could be involved in the final stages of spermatogenesis and spermiation, as has
Ž
been suggested for several species like the New Zealand snapper Pagrus auratus,
. Ž . Ž .
Pankhurst, 1994 , eel Nagahama, 1994 , masu salmon Kobayashi et al., 1997 , striped
Ž . Ž
bass Morone saxatilis, Mylonas et al., 1998 and Atlantic salmon Antonopoulou et al.,
.
1999 . EX and CO groups induced a phase advance pattern of GTH-2 plasma levels,
showing the highest levels concomitant with the maximum percentage of spermiating
males and the highest levels of GSI, which were also shifted accordingly in these
artificial photoperiods. More specifically, in the EX group, the highest levels of GTH-2
were advanced by 4 months with respect to the peak of GTH-2 in NP1 group, while a

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bimodal pattern was observed in CO group in which the first peak was advanced by 3
months with respect to the peak of the NP2 group, and the second peak coincided with
the peak of NP2 group. The meaning of this bimodal behaviour exhibited by the CO
group needs to be further elucidated. However, it is tempting to speculate that the onset
Ž
of these bimodal changes i.e., percentage of spermiating males, peaks of GTH-2 plasma
.
levels was linked to the increasing photoperiod under a compressed photoperiod
regime. This would support the claimed action of photoperiod in fish, suggesting that it
is the direction of change of photoperiod rather than an specific day length that is
Ž .
responsible for the biological response Bromage et al., 1993 .
Serum levels of T and 11-KT in NP groups increased during pubertal development,
reaching the highest values in the middle of the spermiation period and declining as
spermiation progresses. During all the period, 11-KT values followed the same pattern
of variation as T, although they were higher than the corresponding levels of T. This
Ž
androgen profile has also been reported in African catfish Clarias gariepinus, Schulz et
. Ž .
al., 1994 and striped bass Mylonas et al., 1998 . Similarly, maximum T and 11-KT
plasma levels were observed during the middle of the spermiation period in the adult sea
Ž .
bass Prat et al., 1990; Cerda et al., 1997 . Androgens have been proposed as natural
´
inducers of the development of the BPG axis in juvenile teleosts. Our results showed
that the first significant increase in levels of T and 11-KT appeared during the early
phases of the spermiation period indicating that both androgens may be needed for the
initiation of spermatogenesis rather than for spermiogenesis and spermiation. This is
Ž .
supported by results obtained in the rainbow trout by Pavlidis et al. 1994 , showing that
T levels increase shortly before or at the beginning of sperm production. The dramatic
decrease in T levels in February coincided with a peak in GTH-2, when the percentage
of spermiating males was still at its highest rate. These results suggest that a negative
feedback of T on GTH-2 secretion could be acting during the later phases of gonadal
recrudescence when fishes have fully developed gonads. In support of this idea, the
existence of both negative and positive feedback effects of sex steroids on GTH-2
Ž .
secretion have been found in goldfish Carassius auratus, Kobayashi et al., 1997 and
Ž .
Atlantic croaker Micropogonias undulatus, Khan et al., 1999 , while a negative
feedback effect of steroids on GTH secretion has been suggested in rainbow trout
Ž .
Davies et al., 1999 . The androgen profiles in groups exposed to EX and CO
photoperiods were altered, as well the pattern of spermiation and testicular maturation,
suggesting that photoperiod is an important cue in the control of the endocrine events
involved in the first sexual maturation in male sea bass. These shifts in the pattern of
Ž
hormone production and maturation time in groups under accelerating photoperiods i.e.,
.
expanded and compressed , with respect to the control group, have been also reported
Ž
for rainbow trout exposed to a combination of long and short photoperiod Davies et al.,
.
1999 . Both T and 11-KT levels in EX group were low, with respect to the NP1 group,
and presented few changes throughout all the period, especially for 11-KT profile.
Furthermore, the second spawning in the CO group took place without an increase in
androgen levels, although GTH-2 levels were high. This increase in testis weight and
spermiating males without elevated hormone levels could be due to an increase in
testicular sensitivity for these hormones. However, if we look at the ratio between
11-KT and T, the profile presented an interesting variation, in which the highest levels

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246
coincided with the maximum spermiation, irrespective to the photoperiod treatment,
suggesting that 11-KT can be the main circulating androgen in stimulating spermatogen-
esis andror spermiogenesis in male sea bass. These results are supported by the work of
Ž .
Schulz and Goos 1999 in African catfish, suggesting that a balanced production of
Ž . Ž .
11-oxygenated 11-KT and of aromatizable androgens T is crucial to the activation of
the BPG axis during puberty. Similarly, a direct stimulatory effect of 11-KT on
Ž
spermatogenesis has been reported in male Japanese eel Anguilla japonica, Miura et
. Ž .
al., 1991 and in African catfish Cavaco et al., 1998 , indicating that this androgen is an
important endocrine signal to promote spermatogenesis in this species. This is in
contrast with findings reported for mammals, in which the most important androgen in
Ž .
stimulating spermatogenesis is T, instead of 11-KT McLachlan et al., 1996 .
Finally, we can conclude that a negative feedback of T on GTH-2 secretion could be
acting during the first sexual maturation in male sea bass. In addition, we have showed
that both EX and CO photoperiods advance first sexual maturation by at least 2 months
with respect to the controls in male sea bass, but reducing testicular maturation. This
reduction in testicular maturation in both groups could be explained by the non-appropri-
Ž .
ated environmental conditions. Rodrıguez et al. 2001 have reported that juvenile sea
´
bass exposed to EX photoperiods have a low degree of testicular maturation and a rapid
suppression of the reproductive function during the first spawning season, due to the
inappropriate photoperiodic and temperature conditions. Consequently, the modified
pattern of maturation in EX and CO groups could be explained by a shift of the artificial
photoperiods with respect to the natural thermal conditions. Furthermore, the profile of
Ž .
reproductive hormones i.e., GTH-2, T and 11-KT was also altered by both photoperi-
ods, accordingly with spermiation time and GSI pattern.
Acknowledgements
This work was supported by a CYCIT grant MAR97-1883UE and a FAIR grant
CT96-1410 to M. Carrillo. L. Rodrıguez was supported by a grant of the Ministerio de
´
Educacion y Ciencia and a Bancaja-CSIC grant.
´
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