Effects of 11-ketotestosterone and gonadotropin-releasing hormone on follicle-stimulating hormone and luteinizing hormone gene expression in castrated and sham-operated male red seabream <Emphasis Type="Italic">Pagrus major</Emphasis>

ABSTRACT:   In order to clarify the roles of androgen and gonadotropin-releasing hormone (GnRH) on gonadotropin (GTH; luteinizing hormone [LH] and follicle stimulating hormone [FSH]) synthesis, effects of castration and implantation of GnRH analog (GnRHa) or 11-ketotestosterone (11-KT) on expression of GTH subunit, α-glycoprotein subunit (αGSU), FSHβ, and LHβ genes, during the early spermatogenic stage in male red seabream Pagrus major were examined. Male red seabream underwent castration or sham-operation and were subsequently implanted with cholesterol pellets containing GnRHa, silicone capsules filled with 11-KT, or blank capsules (control). FSHβ mRNA levels increased due to castration, and it was reversed by treatment with 11-KT. 11-ketotestosterone treatment also decreased FSHβ mRNA levels in sham-operated fish. These results suggest that 11-KT acts on the pituitary to suppress FSH synthesis in male red seabream. On the other hand, neither castration nor replacement of 11-KT in castrated fish had effects on LHβ mRNA levels, whereas 11-KT treatment had slightly but significantly decreased LHβ mRNA in sham-operated fish. αGSU mRNA levels were not changed by castration or 11-KT treatment in both sham-operated and castrated fish. Meanwhile, treatment with GnRHa significantly decreased FSHβ mRNA levels in sham-operated fish, but not in castrated fish. This suggests that GnRHa may down-regulate expression of FSHβ mRNA through the production of 11-KT in testis. LHβ and αGSU mRNA levels in sham-operated fish, but not in castrated fish, were significantly elevated by treatment with GnRHa.     

Induced ovulation of yellow catfish (Pelteobagrus fulvidraco) using a combination of a gonadotrop‐releasing hormone analogue and domperidone

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.     

Quality of testicular semen of the African catfish Clarias gariepinus (Burchell, 1822) and its relationship with fertilization and hatching success

Quality differences of testicular semen of the African catfish, Clarias gariepinus, and their influence on fertilization and hatching success were investigated. In accordance with an earlier study, two semen types of the African catfish were distinguished according to testicular maturity stage. Semen type I derived from males with white mature testes whereas type II semen derived from males with grey, partly mature testes. Semen volume, sperm cell concentration and seminal plasma pH was significantly higher in type I semen than in type II semen, while sperm motility was similar. Similar fertilization percentages were obtained with semen type I and semen type II. However, the hatching percentage was higher and the percentage of deformed hatched larvae was lower for type I semen. There were significant (P<0.01) positive correlations between sperm motility and fertilization percentage, seminal plasma pH and hatching percentage and a negative correlation between seminal plasma pH and percentage of deformed larvae. Therefore seminal plasma pH and sperm motility are useful to predict semen quality of the African catfish.     

Time course of final oocyte maturation and ovulation in chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> induced by hCG and GnRHa

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.     

外源性促性腺激素诱导日本鳗鲡精子发生和成熟的作用机制

用兔抗血清对抗促黄体素生成素受体（LHR）或称绒毛膜促性腺激素受体（CGR）和雄激素受体（AR）进行LHR和AR免疫组织化学定位,以揭示外源性促性腺激素（鲤脑垂体激素和hCG）诱发日本鳗鲡精子发生及其内分泌机制。结果表明,经过注射激素处理后的实验组与注射前的对照组相比较,其精巢发育和精子发生出现十分显著的变化。组织学切片观察显示,激素处理前鳗鲡精巢处于精原细胞增殖期,而两种激素混合注射后第10天,实验组可见精小叶中精原细胞的有丝分裂和初级与次级精母细胞的数量显著的增加。注射后第35天,靠近生殖上皮除有少量精原细胞外,精小叶中有大量初级精母细胞和次级精母细胞和少数精子细胞以及管腔中存在少量精子。在注射后第83天,日本鳗鲡完成了精子发生和精巢发育成熟以及释精。免疫组织化学染色结果进一步揭示,激素处理前,LH受体免疫活性分布在生殖上皮,显示强的免疫阳性反应;激素处理后,LH受体定位在Sertoli细胞和间质细胞以及精原细胞和初级与次级精母细胞的胞膜上,均显示强的免疫阳性反应。激素处理前,雄激素受体定位在生殖上皮和早期生精细胞的胞膜上;激素处理后,AR则定位在这些生精细胞的核或胞质,而精子细胞和精子显示免疫阴性反应。这些结果首次证明了这两种激素诱导鳗鲡精子发生和成熟的作用机制是通过LH受体和雄激素受体的介导。     

Influence of estradiol-17β, testosterone, and 11-ketotestosterone on testicular development, serum steroid hormone, and gonadotropin secretion in male red sea bream Pagrus major

ABSTRACT:   In order to investigate the influence of estrogen and androgen on reproductive activities of male teleosts, male red sea bream were implanted with silicone capsules containing estradiol-17β (E2), testosterone (T) or 11-ketotestosterone (11-KT) in immature and early spermatogenic stages. One month after implantation of either E2 or T, the gonadosomatic index decreased in accordance with testicular regression in both stages. Implantation of E2 decreased circulating 11-KT levels but did not affect gonadotropin (GTH) subunits, follicle stimulating hormone-β (FSHβ), luteinizing hormone-β (LHβ), α glycoprotein subunit (αGSU) gene expression, and serum LH levels in both stages. Alternatively, T decreased serum 11-KT and LH levels, and FSHβ and LHβ mRNA levels in the early spermatogenic stage but not in the immature stage. These results suggest E2 may directly inhibit testicular development through the suppression of 11-KT production. Meanwhile, T may decrease serum 11-KT levels through the suppression of FSH and LH secretion, resulting to inhibition of testicular development in the early spermatogenic stage. Treatment with 11-KT did not affect the testis in either stage, whereas 11-KT increased LHβ and αGSU mRNA levels in immature, and decreased FSHβ mRNA levels in the early spermatogenic stage. These results suggest that 11-KT may have different effects on GTH subunit gene expression in each reproductive stage.     

促黄体素释放激素和多巴胺拮抗物对鲇促性腺激素释放的作用

以珠江流域鲇为研究对象，分别在性腺发育早期、性腺发育晚期、性腺发育成熟与产卵前期、性腺退化期注射促黄体素释放激素类似物和多巴胺D2受体拮抗物，处理后6h、12h、24h测定血液中的促性腺激素水平变化。结果表明，在性腺发育的各个时期，促黄体素释放激素类似物和多巴胺D2受体拮抗物联合注射能显著剂激鲇促性腺激素分泌；鲇脑垂体促性腺激素的分泌受下丘脑释放的促性腺素释放激素和多巴胺的双重调节，多巴胺只能抑制促性腺素释放激素诱导的促性腺激素分泌。在建立鲇人工繁殖技术时，可采用促黄体素释放激素类似物和多巴胺D2受体拮抗物联合注射方法。     

Effects of gonadotropin-releasing hormone agonist and testosterone on gonadotropin subunit gene expression in female red seabream (Pagrus major)

We examined the effects of gonadotropin-releasing hormone agonist (GnRHa) and testosterone (T) on the level of gonadotropin subunit mRNAs in the pituitary of ovariectomized or intact female red seabream. Ovariectomy induced increase of seabream (sb) GnRH, glycoprotein (GP) α and luteinizing hormone (LH) β mRNA levels. GnRHa treatment also stimulated GPα and LHβ mRNA levels. T treatment reduced GPα and LHβ mRNA expression probably via negative feedback action on sbGnRH. Both GnRHa and T treatment had no effect on follicle-stimulating hormone (FSH) β mRNA levels. These results suggest that the regulatory mechanisms of GPα and LHβ gene expression differ from those of FSHβ gene.     

Thyroxine-induced alterations in the testis and seminal vesicles of air-breathing catfish, Clarias gariepinus

Effect of experimentally induced thyroxine overdose on the testis and seminal vesicles was studied in the air-breathing catfish, Clarias gariepinus during the preparatory and the pre-spawning phase. The present study revealed a marked reduction in testosterone level in serum, testis and seminal vesicles (SV). Histological examination showed a considerable reduction in the number of spermatozoa/spermatids in the seminiferous tubular lumen as well as depletion of fluid in the loculi of SV. SDS-PAGE analysis of SV fluid proteins demonstrated a significant decrease in the level of a ~27 kDa protein in thyroxine treated fishes. Evidences are presented here to indicate that thyroid hormone plays a role in regulating testis and SV function in catfish. T.N. Jacob and J.P. Pandey contributed equally     

Reproduction of striped bass, Morone saxatilis (Walbaum), broodstock: monitoring maturation and hormonal induction of spawning

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.     

Evaluation of HCG-Delivery Systems and Levels on Spawning of Asian Catfish,Clarias batrachus (Linn.)

ABSTRACT

An attempt has been made for multiple spawning of Asian catfish, Clarias batrachus, by sustained hormone administrations through injection and pellet at three different levels of human chorionic gonado-tropin (HCG): 150, 200, and 250 IU. The size of the eggs and biometry of larvae were significantly higher (P< 0.05) in hormone-treated females compared with untreated groups during first as well as second spawning. The administration of all three levels of sustained hormone was also influenced the rate of fertilization and hatching, which were significantly higher (P< 0.05) compared with control group. The total larvae produced by the fish at 200 and 250 IU HCG treatments during both the spawning operations was significantly higher (P< 0.05) than the other groups irrespective of the ways of administration. It was observed that the forms of sustained hormone had no variability on breeding parameters. But the fish can be bred prior to normal season by the use of sustained hormone and those can be again bred during the latter part of the season to augment the seed production.     

Early out-of-season induced spawning of channel catfish Ictalurus punctatus (Rafinesque) conditioned in heated earthen ponds

This study documents early out-of-season induced spawning of channel catfish Ictalurus punctatus. During the early spring (February–April) of 1999, 2000 and 2001, ponds containing (1) male and female channel catfish (mixed-sex ponds) or (2) male channel and blue catfish I. furcatus only, or female channel catfish only (single-sex ponds) were heated to 24–30°C to encourage gonadal maturation and spawning. Unheated ponds were stocked with males and females and were monitored during the duration of heating. When natural spawning occurred in the heated ponds, the fish were captured by seining and unspawned females were injected with 100 μg kg⁻¹ of synthetic leutenizing hormone-releasing hormone. Injected females were either paired with males or held in communal all-female groups, and monitored for ovulation. Eggs were collected and fertilized with sperm of channel catfish or blue catfish. Females paired with males were induced to spawn 44 days (mixed-sex ponds) and 50 days (single-sex ponds) before natural spawning occurred in unheated ponds. Spawning latency (the time between injection and ovulation) and the percentage of neurulated embryos from eggs fertilized using channel catfish sperm was not different between spawning before the natural season (P=0.68) and during the natural season in fish from mixed-sex ponds (P=0.57). Females held in all-female groups produced eggs 34 days before the onset of spawning in unheated ponds. Spawning latency was not different between spawns before and during the natural season (P=0.16), and the percentages of neurulated embryos from eggs fertilized with channel catfish sperm (P=0.76) or blue catfish sperm (P=0.77) before or during the natural season were not different. This study demonstrates the feasibility of conditioning of channel catfish females for early out-of-season induced spawning in the laboratory.     

Hormone Profiles of Captive Striped Bass Morone saxatilis During Spermiation, and Long-Term Enhancement of Milt Production

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.     

Gonadotropin releasing hormone‐analogue (GnRHa) treatment improves the milt production and sperm motility of endangered Caspian brown trout,Salmo trutta caspius,over the course of a spawning season

To determine the effect of gonadotropin releasing hormone‐analogue (GnRHa) treatment on the milt quality of endangered Caspian brown trout, Salmo trutta caspius, the sperm motility (percentage and duration of motility), sperm production (sperm density, spermatocrit and milt volume) and milt pH were measured for GnRHa‐treated (the treatment group) and untreated groups (the control group) during the spawning season. For untreated brooders, the values of the motility per cent, sperm density and spermatocrit decreased continuously during the spawning season while the milt volume, duration of motility and milt pH showed only a significant decrease at the end of the season. For GnRHa‐treated males, these parameters increased 14 days after GnRHa treatment (first milt collection) and then decreased continuously towards the end of the season. In addition, the values of milt and sperm density yielded per treated male were higher than that in the untreated group, although these were not statistically different. In any case, the total sum of yielded milt from the treatment group over the spawning season was higher than that in the untreated group. In this experiment, significant positive correlations were found between milt parameters as follows: sperm motility vs. milt pH; sperm density vs. spermatocrit; milt volume vs. spermatocrit; and milt volume vs. sperm density. The results show that the treatment of Caspian brown trout by GnRHa can improve the milt quality in terms of sperm motility and sperm production during a spawning season.     

Seasonal changes in sexual maturity and fecundity,and HCG-induced breeding of the catfish,Heterobranchus longifilis Val. (Clariidae), reared in Ebrie Lagoon (Ivory Coast)

Oocyte maturation and ovulation were induced with human chorionic gonadotropin (HCG) in the African catfish, Heterobranchus longifilis. Females with a mean oocyte diameter of at least 1.1 mm were used. 100% ovulation was obtained after a single intramuscular HCG injection of between 1.0 and 2.5 I.U./g body weight; a lower dose led to high variability in individual response. Latency time depended more on temperature than on the hormone dose. Eggs could be stripped within 14 h of a dose of 1.5 I.U./g of HCG, at a temperature of 27 to 29°C. After stripping, most of the eggs were fertilized, and high percentages of normal larvae (76% ± 8) were obtained after hatching. Fish hatched in captivity and becoming sexually mature at 1 year of age (mean weight 1.5 kg) were, in turn, artificially reproduced.Seasonal changes in oocyte diameter (determined by periodic intraovarian biopsy of brooders reared in lagoon enclosures) showed a clear decrease in sexual activity at the beginning of the dry season (December) which seemed to be related to higher water temperature. However, even at that time, good quality eggs were obtained after HCG injection. Thus, eggs and fry could be produced all year round, although the mean quantity of eggs collected per female kg proved to be much less at the beginning of the dry season (26 000 ± 14 000) than during the rainy season (68 000 ± 13 000).     

Characterization of the testicular semen of the African catfish, Clarias gariepinus (Burchell, 1822), and its short-term storage

Semen of the African catfish, Clarias gariepinus (Burchell, 1822), was investigated with respect to its cellular composition, sperm cell density, maturation grade, motility and fertility. Storage conditions were tested, whereby sperm viability was assessed by measurement of the motility after activation and by fertility tests. Testicular semen differed in its composition, i.e. the sperm density and numbers of spermatids, according to the maturity grade of the testis. Two semen types could be distinguished: semen type I was characterized by high sperm densities and low numbers of spermatids and semen type II had lower sperm densities and higher numbers of spermatids. Two semen types did not differ in motility and fertility (when adjusted for differences in sperm density). During storage, the sperm viability was influenced by the sodium concentration of the storage medium, temperature, membrane stabilizers as bovine serum albumen (BSA) or hen egg yolk, antibiotics and oxygen. Semen viability was maintained best when it was diluted at a ratio of 1:5 in storage solution (150 mmol L^?1 NaCl, 2.5 mmol L^?1 KCl, 1 mmol L^?1 CaCl₂, 1 mmol L^?1 MgSO₄, 20 mmol L^?1 Tris (pH 8.5) and 0.5% BSA or 0.5% hen egg yolk) and stored at 4 °C. Oxygen gassing and addition of antibiotics (1 mg mL^?1 gentamycine sulphate) to the storage solution affected the two semen types in different ways. Antibiotics had no effect on type I semen, but had a positive effect on type II semen. Oxygen gassing had a positive effect on type I semen but a negative effect on type II semen.     

Retracted: Study of testis histology and sperm morphology in the Bunnei,Barbus sharpeyi (Gunther, 1874) induced by luteinizing hormone‐releasing hormone analogue and carp pituitary extract

This study was conducted to determine the effects of hormone treatment on testis structure in Barbus sharpeyi, as well as the morphology of sperm examined by scanning electronic microscopy (SEM). Male B. sharpeyi were divided into three groups (three fish per group) and injected with luteinizing hormone – releasing hormone analogue (LHRH–A₂) or carp pituitary extract (CPE). The first and second groups were treated with 10 μg kg^?1 LHRH–A₂ and metoclopramide (MET), and their testis were sampled pre‐ and Poststripping respectively. The third group received 2 mg kg^?1 CPE and were killed pre‐stripping. Based on the histological results obtained, the testicular connective tissue of the lumen was thicker, and seminal vesicles were of a lower volume, in fish injected with CPE in comparison to the other groups. After treatment with LHRH–A₂ and MET, not all spermatozoa within the testis were ejaculated, and only a small amount of sperm was obtained by abdominal stripping. The highest and lowest diameters of connective tissue within lobules were observed in fish receiving CPE and LHRH–A₂ treatments respectively. There was a significant difference (P < 0.05) in lobule space between the fish injected with the CPE and the fish injected with the LHRH–A₂ and MET. The SEM results revealed that the spermatozoa of B. sharpeyi were composed of a spherical to elliptical head, a cylindrical midpiece, and a lengthy flagellum. In conclusion, it was found that injection with LHRH–A₂ and MET improved the spermatogenic process in comparison to injection with CPE.     

Molecular characterization,tissue distribution of Follicle‐Stimulating Hormone (FSH) beta subunit and effect of kisspeptin‐10 on reproductive hormonal profile of Catla catla (Hamilton, 1822)

Gonadotropin (GTH) hormones are glycoprotein which stimulates gonadal maturation in vertebrates. Follicle stimulating hormone is involved in initiation of gametogenesis and regulation of gonadal growth. FSHβ has been cloned and characterized from the brain of Catla catla. The FSHβ full‐length of cDNA sequence of 523 bp comprised 3, 394 and 128 bp of 5′‐UTR, open reading frame (ORF) 3′‐UTR respectively. The coding region of C. catla FSHβ encoded a peptide of 130 amino acids. Phylogenetic analysis of C. catla FSHβ deduced amino acid sequence showed high similarity with Gobiocypris rarus followed by goldfish, Carassius auratus. The qPCR result shows that FSHβ mRNA is mainly expressed in pituitary while moderate and low expression was observed in testis and ovary respectively. Chitosan‐nanoconjugated kisspeptin‐10 (CK‐10) of particle size 125 nm, polydispersity index of 0.335 to 0.65 and zeta potential of ?34.95 mV were synthesized and evaluated at against naked kisspeptin‐10 for their reproductive hormonal profile. Treatment of fish with CK‐10 showed controlled and sustained surge of the reproductive hormones (FSH & LH) with peak at 12 h. The hormone levels of naked kisspeptin‐10 treated fish decline after 6 h. The sustained release of this CK‐10 will help in reducing maturation age, synchronization of ovulation and spawning in fish. This is the first report on use of chitosan‐nanoconjugated kisspeptin‐10 (CK‐10) for reproduction in fish.     

Effect of GnRHa injection on milt volume in recently stripped rainbow trout Oncorhynchus mykiss

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.