| Abstract |
The target of the present study was the investigation of the reproductive cycle of
meagre (Argyrosomus regius) as well as the hormonal induction of reproduction using
implants of gonadotropin releasing-hormone agonist (GnRHa). For the study of the
reproduction cycle 7 samplings were performed within a period of 8 months. From
17/11/2009 until 15/3/2010 samplings were performed every 2 months and subsequently
(15/4/2010 – 16/7/2010) monthly. Thirteen fish were used (7 females, 6 males) with an
initial mean weight ± standard deviation 3,828±647 g, which originated from the HCMR
breeding unit in 2005. The stage of gametogenesis was examined during each sampling by
a gentle abdominal massage in males and by gonad biopsy in females. When males were
spermiating, the sperm was stored in ice and then with the use of an appropriate
methodology (Computer Assisted Aperm Analysis, CASA) the basic characteristics of
sperm quality were assessed (annex). In females the fresh sample was examined under an
optical microscope and part of the biopsy was stored in fixation solution in order to be
examined histologically. At the same time, a blood sample was collected in order to
estimate the quantity of steroidal hormones (ng ml-1), testosterone (T) and estradiol (E2) for
females, and testosterone and 11-ketotestosterone (11-KT) for males. The oocytes
presented a gradual increase in their diameter during the samplings and in June the
diameter reached its highest value (574±11.5 μm). On the contrary, a vertical reduction
was noted during July when the recorded diameter was similar to the one of November and
January (128±8.4 μm). Histologically, the gonads contained oocytes in several stages of
oogenesis driving to the conclusion that this species spawns more than once during its
reproductive period. The plasma analysis indicated that the maximum values for both
hormones in females were recorded in May (T=0.2 ng ml-1, E2=0.47 ng ml-1), a month
before the maximum diameter of oocytes. Subsequently, the levels of E2 seemed to return
to low levels similar to the previous months, while T presented a second peak in July
(T=0.16 ng ml-1). Males were spermiating from March to June and produced sperm of
constant density (26.8±7 x109 szoa ml-1) and motility (62±15%). The duration of sperm
mobility was also constant (1.2±0.5 min) and presented a maximum in April (1.94±1.5
min). The plasma analysis for the estimation of steroid hormones level in males indicated a
statistically significant change for both hormones in time. The maximum value for 11-KT
was recorded in March (0.818 ng/ml), whereas for T in July (0.295 ng ml-1). The lowest
values were recorded in November for both hormones. The starting month of spermiation coincides with the maximum of 11-KT, while the maximum of T coincides with the last month of spermiation.
Experiments were performed for the study of the hormonal induction of
reproduction during two successive years (2009-2010). In 2009 during a period of 45 days
three experiments of group induction of spawning were performed. In total 26 fish were
examined (12 females, 14 males) from which 23 (11 females, 12 males) received hormonal
treatment. The fish were placed in three tanks at 5/5/2009 (3 females, 3 males), at
18/5/2009 (4 females, 5 males) and at 9/6/2009 (4 females, 4 males) and they had an initial
mean body weight of 6,934±1,949 g. After the biopsy examination of females under an
optical microscope and the spermiation examination in males, a GnRHa implant (430±150
mg) was administered and the fish were returned in the tank while the spawning was
expected. The first spawning took place two days after the administration of the implant in
all cases, while the mean annual relative fecundity was estimated at 364,993 eggs kg-1 and
the percentage of fertilization at 85±2%. The male individuals which received hormonal
therapy produced sperm with a density of 14±5.3 x109 szoa ml-1. The sperm motility was
estimated at 78±7% and the duration of mobility at 1.8±0.1 min. The relative fecundity and
fertilization for females and density and motility for males were not statistically
significantly different (ANOVA, p≤0.05). The individual experiments on the hormonal
induction of reproduction were performed during the second year (2010). During two time
points, at 4/5/2010 and at 3/6/2010, 3 females and 6 males of initial mean weight
8,238±2,190 g were placed in 3 tanks at a 1:2 ratio following the above process of control
and administration of implants. The first spawning took place two days after the
administration of the implant, while the mean annual relative fecundity estimated at
434,860 eggs kg-1, the mean percentage of fertilization was 92±8% and the number of
spawnings recorded was 11±5. After the first spawn the spawning continued for at least 5
days, and after a 2-day cease at the maximum, the spawning continued. Fecundity
presented a maximum during the first four spawnings and was then gradually reduced until
the end of the spawnings. In the opposite case, the percentage of fertilization remains
constantly above 57% and in some cases reached 100%. There was no statistically
significant difference regarding fecundity and percentage of fertilization either between
individuals or between two different points in time (ANOVA, p≤0.05).
14
In conclusion, the meagre seems to reproduce successfully from April to June,
whereas males produce sperm at the same months. Equally positive results were recorded
after the trial of hormonal induction of reproduction both in May and June and the
production of eggs was estimated at 40,768±36,911 eggs kg-1 spawning-1 with a percentage
of fertilization at 92±8% within 11±5 spawnings. The reproduction of the meager was
possible from April to June but only with hormonal manipulation producing high quality
gametes.
|
Μελέτη του αναπαραγωγικού κύκλου του κρανίου, Argyrosomus regius (Asso, 1801) και ορμονική πρόκληση της αναπαραγωγής του με χρήση εμφυτευμάτων GnRHa
