Suspending Mammalian LHRHa‐injected Channel Catfish,Ictalurus punctatus,in Individual Soft Mesh Bags Reduces Stress and Improves Reproductive Performance

Hormone‐induced spawning of channel catfish held communally in tanks is a reliable method to produce channel catfish, Ictalurus punctatus ♀ × blue catfish, Ictalurus furcatus ♂, F₁ hybrid catfish fry. However, mature catfish are crowded, and repeatedly handled during the process of induced ovulation. Repeated handling of gravid females is stressful and may impair ovulation, egg quality, and reproductive performance. Three trials were conducted to evaluate the effects of two methods of confining post‐hormone‐injected female channel catfish on stress response (cortisol concentrations) and reproductive performance: fish were either held individually while suspended in soft, nylon‐mesh bags or communally in a concrete tank. Percent of females ovulated to hormone treatment, relative fecundity, percent egg viability, and latency of channel catfish did not differ for fish in the two treatments. However, percent hatch and fry/kg of females was higher (P < 0.05) for fish held in bags that for fish held communally in tanks. Mean plasma cortisol response immediately prior to the first hormone injection (0 h) did not differ among fish groups in the two treatments. However, mean plasma cortisol concentrations were significantly lower (P < 0.05) for fish in the bag treatment at 16 and 36 h compared to fish held communally in tanks. Plasma estradiol levels (measure of oocyte maturation) were assessed at 0, 16, and 36 h after hormone injection; concentrations were (P < 0.05) higher at 16 h compared to 0 and 36 h; however, estradiol concentrations did not differ for fish held in the two treatments (P > 0.05). Suspending hormone‐injected broodfish individually in soft bags reduced stress response, improved egg hatching rate, and increased hybrid fry produced per kg weight of female broodfish. Using this simple technology, farmers can improve the efficiency of hatcheries producing hybrid catfish fry.     

Hormonally Induced Spawning, Embryonic Development, and Larval Rearing of the Southern Temperate Banded Morwong, Cheilodactylus spectabilis

Banded morwong (Cheilodactylus spectabilis) are of interest for marine finfish aquaculture in temperate southern Australia. To improve their ovulatory response, adult females were implanted during the autumn spawning season with slow‐release pellets containing 0–400 μg luteinizing‐hormone‐releasing hormone analogue (LHRHa)/kg body weight within 24 h of capture from the wild. Compared to the sham control group, animals treated with LHRHa produced significantly more eggs on each day after implantation for the following 7 d (91 ± 39 and 290 ± 38 mL) and a higher proportion ovulated (8/12 and 27/27). Of fish treated with LHRHa, 93% ovulated 2 d after implantation and 79% ovulated three times at 2‐d intervals, whereas control animals showed no cyclicity of ovulation and few ovulated more than once. Egg production was highest at the first ovulation after LHRHa treatment and declined at subsequent ovulations. In a second experiment investigating the range 100–400 μg LHRHa, there was no effect of dose rate on ovulation parameters, which additionally examined implantation either immediately after capture or after a 5‐d delay. Compared to immediate implantation, a delay resulted in a lower proportion of animals that could be stripped after implantation (100 and 50%, respectively) and the volume of eggs was lower (135 ± 15 and 107 ± 10 mL). The egg quality was poor following delayed implantation, resulting in no fertilization after artificial insemination compared with immediate implantation in which fertilization and hatch rates were higher for eggs collected on Day 2 after implantation (79 ± 8% and 58 ± 9%) than on Day 4 (23 ± 7% and 15 ± 6%). Thus, it is important to implant animals as soon as possible after capture to ensure optimum egg quality. Good‐quality eggs were buoyant and spherical and had a diameter of 1050 ± 25 μm with a single pigmented oil droplet of 190 ± 9 μm. When a separate large batch of eggs collected 2 d after implantation with 100 μg LHRHa was inseminated and cultured at 18 C, larvae hatched after 63 ± 2 h at a standard length of 2.6 ± 0.4 mm. Newly hatched larvae were buoyant and transparent with only a few melanophores, eyes were nonpigmented and jaws were nonfunctional. By the fourth day, jaws were functional and eyes were fully pigmented. Utilization of the endogenous yolk and oil was completed by Day 6, and swimming commenced with exogenous feeding. Larvae, initially fed lipid‐enriched rotifers followed by Artemia, reached 8.9 ± 0.7 mm length on Day 55, after which they metamorphosed to the postlarval paperfish stage of development, 22 ± 0.9 mm on Day 100, and 43 ± 1.0 mm at 6 mo of age. The results show that treatment of wild‐caught females with slow‐release pellets containing LHRHa is effective for the production of eggs for hatchery rearing.     

Induction of ovulation in ornamental common carp (Koi, Cyprinus carpio L.) using LHRHa ([d-Ser(tBu)6, Pro9-NEt]-LHRH) combined with haloperidol and carp pituitary extract

The effects of a single injection of mammalian superactive analogue [d ‐Ser(tBu)⁶,Pro⁹‐NEt]‐LHRHa (20 μg/ kg^?1) combined with the dopamine antagonist, haloperidol (HAL, 0.5 mg kg^?1), for induction of ovulation in the koi carp broodstocks were determined under routine hatchery conditions. The results were compared with classic carp pituitary extract (CPE, double injection) application (water temperature 22 °C). Physiological saline (0.7% NaCl)‐injected fish were used as a control group and no ovulation occurred in this group. The spawning ratio was high in the LHRHa+HAL treatment group and in the CPE treatment group (6/7 and 5/7 respectively). The latency period was 14–16 h in the LHRHa+HAL treatment group and 12–14 h in the CPE treatment group (after the second injection). There was no difference between the two ovulating groups with respect to the spawning index (the weight of eggs as a percentage of female body weight) and fertilization rate of eggs (P>0.05). As a result, ovulation can be induced successfully in koi carp broodstocks with 20 μg kg^?1 [d ‐Ser(tBu)⁶,Pro⁹‐NEt]‐LHRHa+0.5 mg kg^?1 HAL treatment in a single injection without decreasing the egg quality. Application of this combination can be useful for hatchery and broodstock management in koi carp culture.     

Artificial spawning of carp, Cyprinus carpio (L.)

The effect of reproduction was investigated on females of Hungarian strain W, French strain F, and their cross‐breed 1X whose ovulation was stimulated with carp pituitary (0.3 mg kg^?1and, after 12 h, 2.7 mg kg^?1) or Ovopel (one‐fifth of a pellet per kg and, after 12 h, one pellet per kg). It was found that in the case of Ovopel treatment, the percentage of spawning females of strain F and the cross‐breed 1X was higher than in the hypophysed fish compared. The applied ovulation stimulators did not significantly affect the weight of obtained eggs, whereas the significant (P ≤ 0.01) effect was recorded with respect to the quality of eggs after 12‐, 24‐, 36‐ and 48‐h of incubation. After Ovopel stimulation, the quality of eggs was better. The origin of the females had no statistically significant effect on the weight of eggs although the yield of eggs from fish of strain W was much smaller than that from females of strain F and the 1X cross‐breed. The interaction between the ovulation stimulator and the provenance of the females was significant (P ≤ 0.05) for the percentage of live embryos after 48‐h of incubation of eggs. Eggs of the best quality (and highest weight) were obtained from fish of strain F and cross‐breed 1X treated with Ovopel. In females of strain F that spawned within 6 and 10 h after the second Ovopel injection, the effect of the ovulation time on the weight of eggs was non‐significant. It was significant with respect to the percentage of egg fertilization and of live embryos after 36‐h of incubation (P ≤ 0.01 and P ≤ 0.05 respectively). The better quality of eggs (and their higher weight) was recorded when this time was shorter.     

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.     

LHRHa‐induced ovulation of the endangered‐Caspian brown trout (Salmo trutta caspius) and its effect on egg quality and two sex steroids: testosterone and 17α‐hydroxyprogestrone

To induce synchronized ovulation, migrating wild Caspian brown trout (Salmo trutta caspius) females were treated with two interperitoneal injections of Des‐Gly¹⁰, d ‐Ala⁶ LHRH (LHRHa), given 3 days apart. Two injections of 100 μg kg^?1 body weight of this hormone effectively induced ovulation. Within 27 days from the second injection, all fish injected with 100 μg kg^?1 LHRHa had ovulated compared with 54.5% of the controls. The mean time to ovulation was reduced significantly (P<0.05) from 31.67±4.84 days in control fish and 28.83±7.31 days in sham‐treated fish to 16.36±1.61 days in fish injected with 100 μg kg^?1 LHRHa. The fertilization rate in 50 and 100 μg kg^?1 LHRHa‐injected fish was significantly lower than that in the control fish (P<0.05). In fish injected with 50 and 100 μg kg^?1 LHRHa, significant (P<0.05) changes in testosterone (T) and 17α‐hydroxyprogestrone (OHP) levels were observed. After the second LHRHa injection, the fish injected with 100 μg kg^?1 showed the highest serum levels of testosterone and OHP. These results demonstrate that the use of LHRHa can effectively reduce the mean time to ovulation and induce synchronized ovulation in Caspian brown trout.     

Induced spawning of Asian catfish, Clarias batrachus (Linn.): effect of various latency periods and SGnRHa and domperidone doses on spawning performance and egg quality

An experiment was conducted to induce ovulation in Asian catfish, Clarias batrachus, by a single injection of SGnRHa (d ‐Arg⁶, Trp⁷, Leu⁸, Pro⁹, Net) in combination with domperidone. The effects of latency periods, 11, 14, 17, 20 and 23 h, and doses of inducing agent, 10 μg SGnRHa+5 mg domperidone, 20 μg SGnRHa+10 mg domperidone, 30 μg SGnRHa+15 mg domperidone and 40 μg SGnRHa+20 mg domperidone kg^?1 body weight, were studied on the total egg output, stripping response, fertilization, hatching and normal larval production. The highest (P<0.05) number of eggs were stripped at 23 h of post injection of 20 μg SGnRHa+10 mg domperidone kg^?1 female body weight. The highest (P<0.05) stripping response was observed when the females were stripped at 20 and 23 h latency, at all dose levels of the inducing agent. The eggs stripped at 11 h latency did not fertilize, and hence did not hatch irrespective of administration of any dose levels of the inducing agent. The fertilization and hatching per cent of eggs had significantly increased (P<0.05) with increase in latency period to 14–23 h at a dose of 20 μg SGnRHa+10 mg domperidone. The latency period of 14–17 h, and dose of 20 μg SGnRHa+10 mg domperidone and 30 μg SGnRHa+15 mg domperidone kg^?1 of female, was found to be suitable to obtain best spawning performance, and good‐quality egg and larval production in C. batrachus.     

Is the use of recombinant cGnRH may be a future alternative to control the fish spawning? Let us go with the goldfish example

The use of recombinant gonadotropin-releasing hormone (rGnRH) has very rarely been tested in fish to promote spawning. This study evaluated the impact of recombinant chicken gonadotropin-releasing hormone (rcGnRH) with metoclopramide on the release of sex steroids and final maturation induction in goldfish (Carassius auratus) broodstock. For this purpose, goldfish broodstock was divided into four groups and treated with 0.9% NaCl with 20 mg/kg metoclopramide (Met) (C); 10 μg/kg body weight (BW) rcGnRH with 20 mg/kg metoclopramide (rcGn10); 15 μg/kg BW rcGnRH with 20 mg/kg metoclopramide (rcGn15); and 20 μg/kg BW rcGnRH with 20 mg/kg metoclopramide (rcGn20). The capability of the rcGnRH for eliciting biological response was tested in vivo by evaluating the changes of 17β estradiol (E2), testosterone (T), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) and the induced spawning. Blood samples were obtained at 0 h, 12 h, and 24 h after injection. The rcGn10, rcGn15, and rcGn20 treatments induced lower E2 concentration, especially 24 h post-injection. T levels were significantly higher in rcGn10, rcGn15, and rcGn20 treatments 12 h post-injection than at 0 h and then decreased at 24 h post-injection. Furthermore, the rcGnRH tested significantly enhanced DHP secretion in rcGn10, rcGn15, and rcGn20 treatments 12 h post-injection before a decline at 24 h post-injection. No significant difference between the sampling times was found in the C treatment for the 3 sex steroids tested. The results also displayed that rcGnRH at 10–20 µg/kg of body weight can trigger spawning with the highest speed and efficiency of spawning at 20 µg/kg. The obtained results represent a possible strategy for enhancing the artificial reproduction and ovulation of broodstock fish by rGnRH and further support the use of recombinant hormones to promote reproduction in aquaculture.

     

Reproductive parameters of the chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> estimated from human chorionic gonadotropin-induced final oocyte maturation and ovulation in captivity

ABSTRACT:   Final oocyte maturation and ovulation of captive chub mackerel Scomber japonicus with fully yolk-accumulated oocytes were induced by a single injection of human chorionic gonadotropin. Reproductive parameters, including spawning frequency and batch fecundity, which are required to estimate spawning biomass in pelagic fish by the daily egg production method, were analyzed. Germinal vesicle migration (GVM) occurred at 18–24 h post-injection, and the hydration and ovulation of oocytes were completed at 30 and 36 h post-injection, respectively. The results of the maturation process suggest that fish with GVM-stage ovaries captured in the daytime from the field are capable of spawning on the night following their capture. The oocytes used in the oocyte size-frequency distribution method for batch fecundity estimates should be at late GVM and more advanced stages. The results of sequential artificial insemination showed that the quality of ovulated eggs held in the ovarian lumen rapidly deteriorated as time progressed after ovulation. This indicates that the fertilization window for the ovulated eggs of chub mackerel lasts only a few hours, and spawning behavior should be performed within a few hours after ovulation in the wild population.     

Artificial spawning of African catfish Heterobranchus longifilis: differences between the effects on reproduction in females treated with carp pituitary homogenate or Ovopel

The effects of the controlled reproduction of African catfish Heterobranchus longifilis after ovulation stimulation with carp pituitary homogenate (CPH; 4 mg kg^?1; group I) or Ovopel (1/5+1 pellet kg^?1; group II) were investigated. After the application of Ovopel, eggs were obtained from a higher percentage of females than after a CPH treatment (87.5% and 75.0% respectively). The statistically significant (P≤0.05) effect of ovulation stimulator was specified only in the case of the weight of eggs (expressed in grams and in percentage of female body weight), being higher in fish treated with Ovopel compared with CPH‐treated fish (176.02 g, 8.43% and 109.51 g, 5.48%). The quality of eggs expressed in percentage of live embryos after 24 h incubation was higher by 7.5% in fish treated with Ovopel. Latency period did not significantly affect the weight of eggs, fertilization percentage or percentage of living embryos after 24 h of egg incubation. However, the weight of eggs and percentage of living embryos after 24 h incubation were higher in fish spawning after 12 h latency (159.38 g and 85.30%) compared with the weight and quality of eggs obtained from females spawning after 14 h latency (126.15 g and 76.04%).     

Spawning induction of pejerrey Odontesthes bonariensis in captivity using sustained‐release gonadotropin releasing hormone agonist implants

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.     

Investigating factors contributing to reduced embryo survival in farm‐raised Atlantic salmon,Salmo salar L.

Embryo mortality of Atlantic salmon, Salmo salar, has been increasing for more than a decade in the State of Maine, a leading producer of this species in the United States. Increasing embryo mortality not only creates a financial bottleneck for farms but also prevents the sale of surplus eggs as an additional source of revenue. Blood and egg samples were collected at three Maine Atlantic salmon farms from female broodstock at the time of spawning over a 2‐year period. Correlative factors for reduced embryo survival were investigated by measuring egg and maternal plasma concentrations of 17β‐estradiol (E2), 11‐ketotestosterone (11‐KT), testosterone and calcium, as well as maternal hepatic ethoxyresorufin‐O‐deethylase (EROD) activity and fork length. Significant positive correlations were found between maternal plasma concentrations of E2 and 11‐KT and embryo survival. Interestingly, there was no correlation with egg concentrations of sex steroids and embryo survival, suggesting that embryo mortality does not likely rest with the maternal deposition of sex steroids into the egg, but with another hormone regulated process related to egg assembly, ovulation or post‐ovulatory ageing.     

Variation in spawning responses, egg and larvae productions from induced rohu (Labeo rohita) during pre-monsoon and monsoon seasons: Relationship with hormonal changes and oocyte responsiveness during final maturation

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.     

Effects of exogenous neurohormone, gonadotropin (GtH) and dopaminergic drugs on the serum GtH content and ovulatory responsiveness of wild catfish, Silurus asotus (Linnaeus, 1758)

Wild female catfish Silurus asotus (Linnaeus, 1758) were injected with domperidone (DOM) alone, [d ‐Ala⁶, Pro⁹ Net]‐luteinizing hormone‐releasing hormone (LHRH‐A) alone once or twice, LHRH‐A plus DOM once or twice simultaneously at 6‐h intervals, LHRH‐A plus carp pituitary extract (CPE) twice simultaneously at 6‐h intervals and LHRH‐A plus human chorionic gonadotropin (HCG) twice simultaneously 6 h apart respectively. The results indicated that injection of LHRH‐A at a dosage of 0.01–0.02 μg g^?1 body weight (BWt) alone induced a low but significant increase in serum gonadotropin (GtH) (P<0.05) and resulted in a very low ovulation rate, while DOM at a dosage of 5 μg g^?1 BWt alone did not induce an increase in the serum GtH levels and ovulation; in contrast, LHRH‐A at a dosage of 0.01 μg g^?1 BWt plus DOM at a dosage of 5 μg g^?1 BWt (termed the Linpe technique) increased the serum GtH (P<0.05) significantly and induced an ovulatory rate of 100%, while LHRH‐A plus CPE or HCG resulted in an increase in the serum GtH (P<0.05) and high ovulatory rate, although the latency period was longer when fish were given LHRH‐A plus HCG or CPE.     

Effects of emulsified versus saline administration of GnRHa on induction of ovulation in rainbow trout, Oncorhynchus mykiss

The effects of saline-dissolved or Freund's incomplete adjuvant (FIA)-emulsified GnRHa treatment on the induction of ovulation in rainbow trout, Oncorhynchus mykiss, were examined. The FIA-emulsified GnRHa was first diluted in 0.25 ml physiological saline and then mixed with an equal volume of FIA. Fish were selected in the beginning of the spawning season and were allocated into four groups and were treated intraperitoneally with (a) 0.5 ml of emulsified GnRHa (GnRHa–FIA), (b) 0.5 ml saline-dissolved GnRHa in a single injection (GnRHa-1), (c) 0.5 ml saline-dissolved GnRHa in two injections spaced 1 d apart (GnRHa-2) and (d) 0.5 ml of saline (Control). The GnRHa dose in all hormone treatments was 25 µg kg^− 1. All fish in the FIA–GnRHa and GnRHa-2 groups ovulated within 10 and 11 d after treatment, respectively. In contrast, only 75% in the Control fish and 60% of the fish in the GnRHa-1 group ovulated within 36 d after treatment. None of the treatments caused any pre- or post-spawning mortality in the broodstock. Fertilization, eyeing and hatching percentages of the produced progeny were normal in all the treatment groups and did not differ significantly among them. In conclusion, FIA-emulsified GnRHa can be effective in advancing the onset of and synchronizing the ovulation of rainbow trout within a two-week period, thus shortening the egg collection period, without affecting broodstock survival and egg quality.     

Differences in the effectiveness of reproduction among ten breeding strains of the common carp Cyprinus carpio L. after stimulation of ovulation with carp pituitary homogenate or [(D‐Ala6, Pro9NEt) mGnRH‐a + metoclopramide] (Ovopel)

This study focused on the reproduction effectiveness of 10 breeding strains of common carp (Polish strains 2, 3, 6; Hungarian strains 0, W, 7; Lithuanian strain B; French strain F; Israeli strain D and Yugoslavian strain J) after stimulation of ovulation with carp pituitary homogenate or Ovopel. The percentage of females with recorded ovulation became higher after Ovopel treatment in as many as eight breeding strains (2, 3, 6, 0, W, B, F, D). The interaction between the spawning agent and the breeding strain was statistically significant (P ≤ 0.05) for the mass of spawn and non‐significant for traits determining the quality of eggs. Among the 10 breeding strains, in 4 (3, 7, B, J) the least‐squares means (LSM) for the weight of egg (g) were higher for fish stimulated with Ovopel. Among the strains tested, in seven (3, W, F, J, 2, 7, B), the LSM for the percentage of living embryos after 36 h incubation were higher for fish treated with Ovopel. The evaluation of reproduction effects based on the values of such parameters as the percentage of ovulating females, weight of eggs (g) and the percentage of live embryos (36 h) showed that after Ovopel treatment the poorer effects were obtained only for strains 6, 0 and D.     

Induction of sex inversion in common snook (Centropomus undecimalis) males,using 17‐β oestradiol implants

The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that has potential for aquaculture due to its high value and market acceptance. One of the difficulties to its reproduction in captivity is that females are older and bigger than males. The objective of this study was to use 17‐β oestradiol (E2) hormone implants to induce sex inversion in adult males. Fish with an initial body weight of 383 ± 83 g (mean ± SD), individually tagged were used in the experiment. Four E2 dosages (n = 7) were tested (0.5, 1.0, 4.0 and 8.0 mg   kg^?1) in Ethylene‐vinyl‐acetate (EVAc) implants, and a control group (n = 7) implanted without hormone. The parameters evaluated were: survival, weight gain, hepatosomatic and gonadosomatic indices (GSI and HSI) and plasma levels of testosterone (T) and 17‐β oestradiol (E2). Also, liver and gonad morphology was observed through histological sections. GSI was higher in E2 treated than in control fish. All E2 treated fish had completely developed ovaries with oocytes at the perinucleolar stage, while all fish in the control group remained males with evidence of active spermatogenesis. After 15 days, plasma levels of E2 were correlated with the hormone dosage. T levels in the control group were higher than in E2 treated fish, at all sampling times. In conclusion, 0.5 mg   kg^?1 of E2 in EVAc implants is effective to induce sexual inversion in common snook males, which could be useful to obtain broodstock females smaller than in the wild in a reduced time.     

Induction of ovulation in the loach (Paramisgurnus dabryanus) using pimozide and [D-Ala6, Pro9-N-ethylamide]-LHRH

The effects of intraperitoneal injections of [D-Ala⁶, Pro⁹-N-ethylaminde]-luteinizing hormone releasing hormone (LHRH-A) and pimozide (PIM), a dopamine receptor antagonist, on ovulation in loach were investigated. LHRH-A and PIM administered separately were ineffective in inducing ovulation. However, injections of PIM and LHRH-A simultaneously or the injection of PIM 2.5–3 h prior to LHRH-A were highly effective means of inducing ovulation. The simultaneous injection of PIM (1.0 μg/g body wt) and LHRH-A (0.05 μg/g body wt) resulted in a greater ovulatory response than injection of carp pituitary extract (1 pituitary/fish).     

Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, <Emphasis Type="Italic">Platichthys stellatus</Emphasis>

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.     

Diurnal rhythm of serum steroid hormone levels in the Japanese whiting,Sillago japonica,a daily-spawning teleost

Ovarian developmental stages and serum steroid hormone levels were examined at six different times of day (0100, 0600, 1000, 1300, 1600, 2000 h) in a marine teleost, the Japanese whiting Sillago japonica, which has an asynchronous-type ovary containing oocytes at various stages of development and spawns every day during a period ranging up to three months. The largest oocytes in the ovaries at the active vitellogenic or post-vitellogenic stages were found between 0100 and 1300 h. Oocyte maturation indicated by germinal vesicle breakdown (GVBD) occurred at 1600 h, and ovulated oocytes were observed in the ovaries collected at 2000 h. These processes were accompanied by a significant daily change in serum steroid hormone levels. The serum level of estradiol-17β showed a peak in fish with mature oocytes sampled at 1600 h. In these fish, the second-largest oocytes in the ovaries were at the initial stage of vigorous vitellogenesis, the secondary yolk stage. Therefore the highest level of serum estradiol-17β was considered to be due to the second-largest oocytes. Testosterone levels remained low and constant throughout the experimental period. The serum levels of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) peaked at 1600 h at which time all fish had mature oocytes. These results indicate that the Japanese whiting possesses a diurnal rhythm of oocyte development including vitellogenesis, oocyte maturation and ovulation, and further suggest that daily cycles in oocyte growth and maturation which simultaneously take place in an ovary are regulated by diurnal secretions of estradiol-17β and the maturation-inducing steroid, 17α,20β-diOHprog.