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1.
Abstract. A domestic striped bass. Morone saxatilis (Walbaum), broodstock was established by rearing fish to sexual maturity in ponds. A method was developed to reproduce the domestic females, and also wild females too immature to be successfully induced to spawn with injected human chorionic gonadotropin (hCG). The fish were implanted with pellets containing 100–150μg of a synthetic analogue of mammalian gonadotropin reieasing-hormone, [D-Ala6- Pro9-NEt]-LHRH (mGnRHa), in a matrix of cholesterol (CH) and cellulose. They were implanted with one fast hormone-release (80% CH) pellet and one slow hormone-release (95% CH) pellet and allowed to mature for 1–3 days, until they entered the process of final oocyte maturation and were induced to ovulate or spawn with an hCG injection. The secondary hCG injection was found to be necessary to speed the maturation of the wild fish; they otherwise would succumb to the stresses of capture, handling and confinement before they could be spawned. The total mGnRHa dosages used ranged from 33 to 111μg mGnRHa/kg body weight, and the hCG doses were either 165 or 330 IU hCG/kg body weight. Using the combined mGnRHa implant-hCG injection technique, fry production rates were comparable to those obtained using fully mature wild females taken directly from their spawning grounds.  相似文献   

2.
Abstract:   The question of whether the ovulation and spawning time in chub mackerel Scomber japonicus is entrained by a circadian rhythm was raised by our previous experiments. Further questions were also raised about whether the time course of human chorionic gonadotropin (hCG)-induced final oocyte maturation (FOM) and ovulation reflected the natural time course induced by endogeneous pituitary gonadotropin (GtH). To address these questions, hCG and gonadotropin-releasing hormone analog (GnRHa) were administered at two 'opposite' times, 14:00 and 02:00 hours, and the time courses of FOM and ovulation were compared. When hCG was injected, ovulation occurred 33 h post-injection in both groups, regardless of the timing of the hCG injection. The timing of ovulation in chub mackerel depends on the timing of hCG injection, but apparently not on circadian rhythms. When GnRHa was injected, ovulation began at 36 h post-injection of GnRHa, regardless of the timing of injection. These results indicate that the time course of FOM and ovulation in the chub mackerel followed a similar pattern whether stimulated by hCG injection or spontaneous luteinizing hormone (LH) surge because GnRHa induces the secretion of endogenous GtH (primarily LH) from the fish pituitary. Thus, it is concluded that the time course of hCG-induced FOM and ovulation in chub mackerel follows the natural time course induced by endogenous pituitary LH.  相似文献   

3.
The present study was designed to examine the potential for inducing ovulation in starry flounder (Platichthys stellatus) using gonadotropin-releasing hormone analog (GnRHa) and human chorionic gonadotropin (hCG) to assess whether starry flounder are differentially responsive to GnRHa and hCG. Female starry flounder were injected or implanted with different doses of hCG or GnRHa pellets to examine their ovulation-inducing potential and effects on plasma levels of testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Blood samples were collected for up to 10 or 25 days post-injection or post-implantation in two separate experiments designed to mimic the early and middle stages of spawning, respectively. Fish treated with the GnRHa pellets (100 µg) showed a significant increase in the total number of stripped eggs relative to the controls. GnRHa administration had no effect on the floating rate or fertilization rate of ovulated eggs in the both experiments, whereas hCG injection affected both of these rates. Plasma T levels were not significantly different between the exogenous hormone-treated and control fish. In contrast, the plasma E2 level was elevated in those fish treated with GnRHa, regardless of injection or implantation, and was accompanied by increased numbers of stripped eggs in both experiments. Treatment with GnRHa resulted in higher 17,20βP levels compared to the controls, and there was a positive relationship between elevated plasma 17,20βP and an increase in ovulated eggs in response to GnRHa treatment. The implantation of starry flounder with GnRHa-containing pellets was effective at inducing sustained ovulation compared to hCG treatment.  相似文献   

4.
The effects of an intraperitoneal hormone injection of gonadotropin‐releasing hormone agonist (D‐Ala6, Pro9‐NEt GnRHa) alone or in combination with a dopamine antagonist, domperidone (DOM), on ovulation induction in yellow catfish Pelteobagrus fulvidraco were tested. The hormone treatments were as follows: 6 mg kg−1 body weight (BW) of carp pituitary extract as a positive control, GnRHa 10, 20, 40 and 80 μg kg−1 BW and a combination of GnRHa and DOM as follows: 10 μg+5 mg, 20 μg+10 mg, 40 μg+20 mg and 80 μg+40 mg kg−1 BW. Physiological saline (0.7% NaCl) was used as a negative control. Significant differences in the ovulation ratio, latency period and ovulation index (OI) were observed among treatments (P<0.05). The combination of GnRHa and DOM at doses of 40 μg+20 mg kg−1 BW had higher values of the ovulation ratio and OI, and a shorter latency period compared with other treatments. The highest OI in GnRHa treatments was only 56.67%, suggesting a dopaminergic tone on gonadotropin secretion in this fish at the pre‐ovulatory stage. Therefore, ovulation can be successfully induced in yellow catfish with 40 μg kg−1 GnRHa+20 mg kg−1 DOM without affecting the egg quality.  相似文献   

5.
Abstract Levels of gonadal steroid hormones were quantified in an adult striped bass, Morone saxatilis (Walbaum), broodstock during their gametogenic cycle. Blood plasma concentrations of Estradiol (E2) and testosterone in females, or 11-ketotestosterone(11-KT) and testosterone (T) in males, were used as indicators of maturation. In both sexes, hormone levels were low in summer but increased significantly by late October to intermediate levels which were then maintained until late January. They then increased again rapidly to maximum pre-spawning values attained in late February or March, and subsequently decreased during the spawning period (April and May) with an increased incidence of spent fish with low hormone levels. The changes in blood hormone concentrations coincided with annual changes in photoperiod and water temperature that may be useful landmarks for maturation in captive broodstock. Mature females were implanted with pellets containing a dose of approximately 20 μg/kg body weight of [D-Ala6-Pro9-Net]-LHRH (GnRHa) in a matrix of cholesterol (CH) and cellulose. In April, they had not yet begun final oocyte maturation (FOM) and were too immature for conventional induction of spawning by injection with human chorionic gonadotropin (hCG). In early April, females given two 95% CH (slow hormone-release) GnRHa pellets (95/95) or females given one 80% CH (fast hormone-release) GnRHa pellet and one 95% CH GnRHa pellet (80/95) spawned within 13 days treatment (n= 4) with good egg fertility (76 ± 7% of total) and hatch rates (62 ± 15% of fertile). Females given dual fast-release GnRHa pellets (80/80) or control (Sham) pellets did not spawn or show evidence of increased oocyte diameter or development. In late April, four of six females given the 80/95 GnRHa pellet combination spawned within 9 days. Three fish produced fertile eggs (54 ± 18%). one spawned overripe eggs, and the remaining two increased oocyte diameter and maturation. Three corresponding controls did not spawn, and two of these showed clear signs of atresia within 11 days. In early May, some females were undergoing early FOM and were mature enough to be spawned by hCG injection. Three were given a single 80% CH GnRHa pellet and spawned within 6 days of treatment to produce fertile eggs (44 ± 6%). Of two other females given dual 80% CH GnRHa pellets, one spawned infertile eggs and the other failed to spawn within 9 days. GnRHa implants show promise as a technique for inducing spawning of captive striped bass broodstock although the optimum hormone delivery systems, dosages and release rates should be verified for fish at specific maturational stages.  相似文献   

6.
Pigfish, Orthopristis chrysoptera, readily undergo vitellogenesis in captivity, but final oocyte maturation (FOM), ovulation, and spawning can be unpredictable. The objectives of this investigation were to assess the effects of various doses of Ovaprim® (sGnRHa [salmon gonadotropin‐releasing hormone analog] + domperidone) and human chorionic gonadotropin (HCG) on FOM, ovulation, and spawning in pigfish. Ovaprim dosages investigated were 0.25, 0.50, 1.00, and 2.00 mL/kg, which were injected into the dorsal musculature of female pigfish. Male pigfish received one half the dosage administered to females to ensure spermiation. HCG doses of 500, 1000, 2000, and 4000 IU/kg were administered to female pigfish, with male pigfish once again receiving half the female dosage. Eggs were collected over a 72‐h period postinjection and enumerated and assessed for fertilization, hatching percentage, and survival to first feeding. Eggs and larvae were photographed and a suite of morphological parameters was determined. Hormone dose evaluations with pigfish showed that the low‐dose (0.25 and 0.50 mL/kg) Ovaprim treatments resulted in better spawning performance. However, superior egg and larval characteristics validate the 0.50 mL/kg dose as the preferred choice for use with pigfish. The four doses of HCG administered to pigfish performed unreliably in this study; thus, no dose recommendation could be made.  相似文献   

7.
This study examined the changes in plasma steroids during natural (Experiment 1) and induced (Experiment 2) final maturation in yellow perch Perca flavescens. In experiment 1, ovulating yellow perch were stripped of eggs and blood samples collected to determine the concentrations of testosterone (T), estradiol-17β (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Eggs from individual females were weighed and fertilized. Fertilization rate was determined at the embryo eyed stage. In experiment 2, females were randomly assigned to one of the following treatment groups: (1) saline (0.7% NaCl), (2) des-Gly10[D-Ala6] LHRH-ethylamide (100 μg LHRHa/kg), and (3) LHRHa plus 17,20βP (100 μg LHRHa/kg + 2 mg 17,20βP/kg). Fish were injected intraperitoneally with two doses at a two-day interval. Blood was collected prior to injections and at the time of ovulation/spawning and concentrations of T, E2, and 17,20βP (free and conjugated) were determined. In experiment 1, low concentrations of 17,20βP were recorded at spawning. In experiment 2, all surviving fish injected with LHRHa (5 of 5) released their eggs spontaneously during the week following injections. None of the surviving control fish (0 of 5) ovulated during this period, whereas only 1 of 3 surviving fish injected with LHRHa + 17,20βP released eggs. In the control group, concentrations of E2 and 17,20βP did not show significant differences over the experimental period, whereas plasma T concentrations increased significantly. In fish injected with LHRHa, the concentrations of T and 17,20βP increased significantly after the first injection but then declined at ovulation/spawning. It also appears that 17,20βP was conjugated to its sulfated form. Mortality reached 62.5% in the group injected with LHRHa + 17,20βP indicating that this treatment was severe. Thus, LHRHa alone appears highly effective in inducing ovulation in yellow perch. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
In broodstocks of Atlantic halibut, Hippoglossus hippoglossus, male and female gamete production often becomes unsynchronised towards the end of the spawning season—milt becomes very viscous and difficult to express while the females are still producing batches of good quality eggs. Gonadotrophin-releasing hormone agonist (GnRHa) has been shown to stimulate spermiation in a number of fish species. Therefore, we conducted two experiments where male halibut were implanted intramuscularly with pellets containing GnRHa. The effect of the pellets was tested at three periods: before, at the height of and at the end of spermiation. In the middle period, GnRHa was tested at two doses (5 and 25 μg/kg bodyweight). Measurements were made of milt hydration, sperm motility and fertilisation rate. Implanted males began spermiation at least 4 weeks before control males. Both doses of GnRHa increased the fluidity of the milt. This effect lasted for at least 20 days in the low dose group and for 40 days in the high dose group. When applied at the end of the season, GnRHa reversed the normal trend for the milt to become more viscous. GnRHa treatments did not affect fertilisation rates obtained with the sperm. However, towards the end of the spawning season, sperm motility was enhanced in males treated with the high dose of GnRHa (25 μg/kg) compared to controls. As described previously, plasma concentrations of the gonadal steroids, 5β-pregnane-3β,17,20β-triol 20-sulphate and 17,20-dihydroxy-4-pregnen-3-one, were significantly enhanced by GnRHa treatment. Concentrations of testosterone on the other hand decreased when spermiating males were treated with GnRHa. Our data suggest that 17,20β-dihydroxy-4-pregnen-3-one or its metabolites are involved in milt hydration, possibly through affecting ion transport.  相似文献   

9.
Jundiá (Rhamdia quelen) is an important species for aquaculture in temperate and subtropical climates. In the present study, the results of different forms of GnRH analogue treatments on ovulation in jundiá have been compared with those from treatment with carp pituitary. Seven out of eight females ovulated in groups treated with carp pituitary (4.0 mg kg?1 BW) and Ovaprim (0.5 mL kg?1 BW). Injection with sGnRHa (10 μg kg?1 BW) combined with metoclopramide (20 mg kg?1 BW) caused a significantly lower rate of ovulation with three out of eight females responding. None of the fish injected with sGnRHa (10 μg kg?1 BW) alone ovulated. Mean PGSI [(weight of stripped egg mass/BW of the female before stripping) × 100] and mean fertilization rate values were high and similar between treatment groups. The obtained results indicate that in jundiá, there is a strong dopamine inhibitory tone on gonadotropin secretion. The gonadotropin releasing activity of sGnRHa can be potentiated by dopamine receptor antagonists and the combined treatment is effective in inducing ovulation. In this regard, domperidone proved to be more potent than metoclopramide.  相似文献   

10.
In this study, the effect of gonadotropin‐releasing hormone agonist (GnRHa) injection on milt production in spent rainbow trout was investigated. On day 0, 25 newly matured male rainbow trout (Oncorhynchus mykiss) were stripped manually, and sperm quantity (vol: mL fish?1) and quality, spermatocrit (%), sperm count (cell mL?1), motile sperm percentage and motility duration (s) were evaluated. After stripping, fish were randomly divided into five groups: intact; sham (injected with propylene glycol as a hormone vehicle); and groups receiving 4, 8 or 16 μg kg?1 BW of [d ‐Ala6 Des‐Gly10] mGnRHa. On day 7, the fish were stripped again and the same sperm characteristics as on day 0 were measured. At the beginning of the experiment, there were no significant differences in any of the sperm quantity characteristics between groups. On day 7, expressible milt volume was significantly reduced compared with day 0 (P<0.05, t‐test) in the intact and sham groups but milt quality remained the same (P>0.05, t‐test). The present study shows that GnRHa injection with a concentration as low as 4 μg kg?1 BW after first stripping could prevent a significant reduction in milt quantity collected 7 days later without any adverse effects on sperm quality.  相似文献   

11.
Abstract— Plasma profiles of reproductive and thyroid hormones were studied in captive striped bass Morone saxatilis during an 11-wk period encompassing the spawning season, and the effect of a sustained-release gonadotropin-releasing hormone agonist (GnRHa)-delivery system (GnRHa-implant) on milt production was evaluated. The highest percentage of spermiating fish was observed between mid-April and mid-May, and mean total expressible milt ranged from 3.5 to 6.0 mL/kg. Plasma gonadotropin II (GtH II) increased significantly, though inconsistently, during the spermiation period, whereas testosterone and 11-ketotestosterone levels declined continually. Plasma 17,20β-dihydroxy-4-pregnen-3-one and 17,20β,21-dihydroxy-4-pregnen-3-one remained low and unchanged during the peak of the spermiation period, while thyroid hormones were high and fluctuated without exhibiting a trend consistent with spermiation. The observed endocrine profiles suggest that captivity can diminish plasma GtH II and triiodothyronine levels in striped bass. Transfer of spermiating males from large holding tanks to small spawning tanks reduced total expressible milt after 14 d, but treatment with a GnRHa-implant restored milt volume, presumably due to the prolonged elevation of plasma GnRHa and GtH II induced by the GnRHa-implant. Also, treatment with the GnRHa-implant induced a two- to four-fold elevation of expressible milt for at least 20 d compared to control fish, while resulting in only a 5 to 15% decrease in sperm density. It appears that captivity and hatchery operations can diminish milt production in striped bass, and that GnRHa-delivery systems, via sustained elevation of plasma GtH II, can induce long-term enhancement in milt volume without affecting sperm density greatly.  相似文献   

12.
Spermiated male greenback flounder (Rhombosolea tapirina) were implanted with gonadotropin releasing hormone analog (GnRHa) pellets at different dosages to examine their effects on milt characteristics and plasma levels of testosterone (T), 11-ketotestosterone (11KT) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Milt and blood samples were collected for up to 28 or 42 days post-implantation (p.i.) in two separate experiments using fish that were slightly or moderately spermiated, respectively. In both experiments, fish treated with GnRHa pellets showed a consistent and significant increase in milt volume relative to controls, and the increase of milt volume was more rapid than the increase in numbers of spermatozoa. Spermatocrit (Sct) was significantly lower in GnRHa-treated fish than in controls. Plasma levels of T and 11KT were elevated at 7 and 14 days p.i. in slightly spermiated fish treated with GnRHa and elevated plasma T and 11KT levels were accompanied by increased milt volume early in the spermiation period. In contrast, there was no significant difference in plasma T levels between GnRHa-treated and control fish in fish that were moderately spermiated at the time of implant. Treatment with GnRHa tended to result in lower plasma levels of 11KT and higher levels of 17,20βP relative to controls, and there was a positive relationship between the elevation of plasma 17,20βP and the increase in milt volume in response to implantation of GnRHa pellet. Slow release GnRHa administration had no effect on sperm activity or pH and osmolality of seminal plasma in either experiment.  相似文献   

13.
Hormone Induced Spawning of Summer Flounder Paralichthys dentatus   总被引：2，自引：0，他引：2  
During their first year in captivity, summer flounder Paralicthys denratus were induced to spawn with gonadotropin releasing hormone analogue (GnRHa) implants, injected carp pituitary extract (CPE) or human chorionic gonadotropin (hCG) injections. The percentage of fertile eggs was greatest (69%) in CPE-treated females. CPE, but not GnRHa or hCG, was capable of stimulating oocyte growth (increased follicle diameter during vitellogenesis) followed by ovulation. Fish with maximum ovarian follicle diameters between 180 and 435 μm at the initiation of CPE injections produced the greatest percentage of fertile eggs. For most females, fertilization rate was greatest for the first batch of eggs ovulated. The mean fertilization rate for the first spawn of CPE-treated fish was 42% compared with 14% for the second spawn from the same fish. Fish with maximum initial follicle diameters of 585 40 μm that were implanted with GnRHa ovulated the greatest number of eggs, but fertility was low and variable. Approximately 35% of females injected with hCG ovulated a limited number of eggs, but only one hCG-treated female produced fertile eggs. Only a limited number of spermiating males were available for spawning trials. Hormone treatments used on females were ineffective for inducing or maintaining spermiation in male summer flounder.  相似文献   

14.
The aim of the present study was to study spawning stimulation in artificial reproduction of females pikeperch (Sander lucioperca L.) using “Chorulon” containing the human chorionic gonadotropin (hCG) and compare with “Supergestran” containing a mammalian GnRH ([D-Ala6]GnRHProNhet) analogue. The females were divided into eleven experimental groups and injected with hCG at 250, 500, 750, and 1 000 IU kg?1 body weight (BW) and mGnRHa at 1, 2.5, 5, 10, 25, and 50 μg kg?1 BW. In all treatments, a single intramuscular injection of hormone was performed. Control group was injected with 0.9 % NaCl, 0.9 cm3 kg?1 BW. The average percentages of ovulating females were 88.5 ± 12.3 and 80.8 ± 10.9 % in hCG- and mGnRHa-treated groups, respectively. The average diameter of eggs was 0.95 ± 0.06 and 0.98 ± 0.06 mm in hCG- and mGnRHa-treated groups, respectively. Neither ovulation rate nor diameter of egg was statistically differed among hormonally treated groups. Statistical difference was observed only in hatching rate, where the average were 73.6 ± 14.4 and 50.6 ± 17.7 % in hCG and mGnRHa-treated groups, respectively. Among hormonally treated groups, the best results were observed in groups treated with hCG at 500 and 750 IU kg?1 and in groups treated with mGnRHa at 25 μg kg?1. No ovulation was observed in the control group. This study indicated successful ovulation in pikeperch using a single intramuscular injection of hCG or mGnRHa analogue.  相似文献   

15.
Female greenback flounder Rhombosolea tapirina were treated with either des Gly10 [D-Ala6] LHRH ethylamide (LHRH-a) at 50 or 100 pg/kg intraperitoneal injection (ipi), LHRH-a cholesterol pellet (LHRH-a pellet) 100 μg/kg implanted intraperitoneally, or human chorionic gonadotropin (hCG) 1,000 IU/kg ipi. Treatment with hCG, LHRH-a (50 μg/kg) ipi and LHRH-a pellet increased the total number of ovulations above control levels. LHRH-a (100 μg/kg) ipi was not consistently more effective than the control and both LHRH-a (50 μg/kg) ipi and LHRH-a pellet induced more ovulations than LHRH-a (100 μg/kg) ipi. Of those fish that ovulated, most ovulated more than twice, and most ovulations occurred at daily intervals. Oocyte diameters increased and oocyte stage advanced significantly in response to all exogenous hormone treatments. This was accompanied by increases in plasma and ovarian levels of 17β-estradiol (E2, and in most cases, plasma and ovarian levels of testosterone (T). Plasma and ovarian levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were not consistently elevated in association with reproductive events.  相似文献   

16.
The aim of this study was to induce and synchronize spawning of pejerrey Odontesthes bonariensis (Valenciennes, 1835), using gonadotropin releasing hormone agonist (GnRHa) implants. In the first experiment, the ovarian condition was assessed by ovarian biopsies and the measurement of the genital pore width (GPW). Females having the leading clutch of oocytes with a diameter of around 800–900 μm and a GPW between 4.5 and 5.5 mm were treated with GnRHa implants. Eighty per cent of females spawned between 2 and 9 days after treatment, 12 days earlier than 20% of the fish in the control group that presented signs of spawning activity. In order to avoid any possible ovarian injury and/or stress by the catheterization procedure, in a second experiment, females were selected only by visual inspection of the abdomen and GPW measurement. As in experiment 1, 80% of females spawned between 2 and 8 days after treatment, 8 days earlier than 30% of the fish that spawned in the control group. In both experiments, fertilization and hatching success were similar between control and GnRHa‐treated groups. These results clearly demonstrated that GnRHa implantation can advance and synchronize ovulation and spawning in pejerrey without affecting egg quality.  相似文献   

17.
Scombridae species, such as tunas and mackerels, often do not spawn in land-based fish tanks without hormone treatment. To induce spawning in various fishes, a gonadotropin-releasing hormone analogue (GnRHa) is often administered by pellet implantation. Noninvasive administration is desired to induce spawning in scombrids that are sensitive to handling stress. Spawning induction by oral administration has been reported in several fishes, yet this method has not been put into practice in the aquaculture industry since a considerable amount of GnRHa is needed. Utilization of peptide synthesizers is widespread, and antigen-grade GnRHa (AgGnRHa) produced by a custom-peptide supplier is approximately 100-fold cheaper than conventional reagent-grade GnRHa (RgGnRHa), although the purity of AgGnRHa is lower. Here, we confirmed that the spawning induction potency of AgGnRHa was similar to that of RgGnRHa by pellet implantation in blue mackerel Scomber australasicus. Oral administration of AgGnRHa [6.0 mg/kg body weight (BW) per day] showed an equivalent ability to induce spawning of the mackerel as pellet implantation (0.1 mg/kg BW). We could also induce spawning of eastern little tuna Euthynnus affinis by oral administration of the AgGnRHa. Further, the obtained eggs showed higher survival. Thus, the oral delivery of AgGnRHa could be a powerful tool to induce spawning in Scombridae.  相似文献   

18.
11-ketotestosterone (OT) is a typical androgen of male teleost fish, but information on the question if it is involved in the feedback regulation of pituitary gonadotropin II (GTH-II) secretion is controversial. We have therefore studied the effects of OT on gonadotropin releasing-hormone (GnRH) stimulated GTH-II secretion in male African catfish Clarias gariepinus). In vivo experiments were carried out with intact and castrated fish. OT plasma levels were increased by implantation of silastic capsules containing 11-ketoandrostenedione (OA) which is converted to OT in both intact and castrated fish. When intact males received OA- or blank-capsules, treatment with salmon gonadotropin releasing-hormone analogue (Des-Gly10-D-Arg6-sGnRH-NEt; 0.2 μg sGnRHa/kg body weight) elevated the plasma GTH-11 levels in both groups. However, the levels were about 2 times higher in blank- than in OA-implanted fish. When castrated fish received either blank-or OA-capsules, sGnRHa treatment led to plasma GTH levels significantly higher than in sham-operated fish. However, there was no difference between the blank- or OA-implanted castrates, though OA implantation led to a restoration of OT plasma levels. This suggests that replacement ofOT is insufficient to reverse castration-induced effects. In vitro experiments were carried out with pituitary tissue fragments using a static culture system. The tissue remained sensitive to sGnRHa (5 × 10?9M) for 4 days after the beginning of incubation. Preincubation of pituitary tissue for 24 hours with 25 ng OT/ml medium (80 nM) completely abolished the stimulatory effect of sGnRHa on GTH-II secretion. Tritiated OT was not metabolized by pituitary tissue during 6 hours of incubation. We conclude that 11-ketotestosterone, a quantitatively prominent and non-aromatizeable circulating androgen participates, at least in part by direct action on the pituitary, in the negative feedback regulation of GnRH-stimulated GTH-II secretion in male African catfish.  相似文献   

19.
Early induced spawning in captive rohu (Labeo rohita) often encounters with reduced spawning performances and devaluation of final product. The present study attempted to gain insight into the problems associated with poor performance of rohu during pre-monsoon spawning. A combination of sGnRHa and domperidone was used to induce final oocyte maturation (FOM) and ovulation in rohu during early (pre-monsoon, PM) and normal (monsoon, MN) spawning. The spawning performance parameters such as, spawning response, production and quality of egg and larvae showed significantly lower values (p < 0.05) in PM, when compared with MN spawning. The egg and spawn productions were recorded as 2.6 ± 0.05 and 2.41 ± 0.05 during the MN season, which were reduced by almost 50% in the PM season. Moreover the quality of egg and hatchling was devaluated significantly (p < 0.05) and exhibited higher percentage of mortality and abnormality in PM than those recorded in the MN season. The plasma concentration of carp gonadotropin (cGtH), 17β-estradiol (E) and 17α20β-dihydroxy-4-pregnen-3-one (DP) in relation to progress of FOM and ovulation at different seasons exhibited marked variation in hormonal profiles particularly in E and DP of PM fish. Higher initial plasma E (3.8 ± 0.3) and a distinct E peak clearly indicated the lack of transition from vitellogenic to post-vitellogenic stages that prevailed in PM rohu. Delayed DP and cGtH surge during FOM and ovulation resulted in longer latency period in spite of higher water temperature (31.5 °C) that prevailed during the PM period. In-vitro study on oocyte maturational competence (OMC) clearly depicted the lack of maturational competence in ovarian follicles during PM than MN in rohu. However priming the fish with purified carp gonadotropin (PCG) enhanced the acquisition of OMC in PM rohu in such an extent, that no marked seasonal differences (p > 0.05) in OMC were remained further, when compared with MN follicles. The PCG mediated acquisition of maturational competence was found to be dependent fully on new mRNA and protein synthesis in PM fish. The present study clearly demonstrated that the oocytes' unresponsiveness to hormonal induction was mainly responsible for reduced spawning performance in PM rohu, which could be ameliorated through PCG priming to achieve better spawning response in rohu during the pre-monsoon period. Thereby, the rohu fry production could be initiated successfully as early as May, allowing public and private hatcheries to produce larger age-0 rohu fingerlings ensuring reliable steady source of stocking materials for grow-out system earlier in the season.  相似文献   

20.
A high percentage (98.3%, N = 60) of the marbled grouper Epinephelus microdon individuals captured from spawning aggregations during July and August 1993 in the waters surrounding the island of Koror, Republic of Palau, Micronesia, were in the stage of maturity at which final maturation and spawning could be hormonally induced. The sex ratio of the captured fish was highly skewed towards males (4 male:1 female). Sexually immature females comprised the smallest size class, (<0.6 kg body weight (BW) or 33.0 cm total length (TL)), while sexually mature females were restricted to the 0.6–1.5 kg BW (33.0–46.4 cm TL) groups. Males predominated in size classes >0.6 kg BW, and individuals >1.5 kg BW (46.4 cm TL) were exclusively male. All females with oocytes that averaged ( N = 50) >400 μm in diameter were successfully induced to spawn by a two-injection protocol using human chorionic gonadotropin (HCG) at total dosages of 2,100–3,200 IU/kg fish. All males used in the spawning trials were administered a single injection of HCG at dosages of 500 or 1,000 IU/kg fish. Fecundity ranged between 7.96 × 105−1.24 × 106kg BW, average spawned egg diameters ranged between 769–832 μm, percent fertilization ranged between 32.6%–99.9%, and hatching percentages were >90.0%. Total fat content of eggs obtained from a pooled spawning event was 14.1 mg/100 mg dry weight. The data indicate that HCG is a suitable treatment for the induction of spawning in marbled grouper females that possess a mean oocyte diameter of 400 μm or greater.  相似文献   

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