Induction Of Spawning Research Articles

Perivisceral coelomic fluid as a mediator of spawning induction in tropical holothurians

Summary Holothurians are among the most commercially valuable echinoderms for which successful spawning induction under laboratory conditions is still difficult to obtain on a reliable basis. The present study demonstrates that the transfer of perivisceral coelomic fluid (PCF) can be used as a reliable tool to induce spawning in mature individuals. PCF collected from holothurians that had been in the typical spawning posture, without shedding gametes, for ca. 20 min triggered spawning in 71 to 100% of conspecifics. The individuals responded to the injection of a 2–3 ml aliquot by displaying the spawning posture within 30–62 min and by massive gamete broadcast 57–83 min later. The results varied according to the time of PCF collection with respect to the spawning activity of the donor and the amount of PCF injected. The inductive substance was found not to be sex—specific since positive responses were observed in individuals of the same or opposite sex as the donor. The PCF of a spawning donor was also active when added to the surrounding seawater, as it induced the typical posturing in 47–65% of mature individuals and subsequent gamete release in 20–31% of them less than 85 min later. PCF collected from immature or non—spawning individuals did not induce spawning. Although most experiments were performed with Bohadschia argus, similar results were obtained with B. marmorata, Holothuria leucospilota and H. atra. Inter—specific trials were also successful, inferring that the chemical involved is not species—specific. Nonetheless, PCF from spawning asteroids and echinoids did not induce spawning behaviour or gamete release in holothurians. The results showed that holothurian PCF acts as a carrier of inductive substances during spawning. Its efficacy even when diluted in seawater could partly explain the epidemic arid synchronous spawning observed in some holothurian populations.

More effective induction of spawning with long-acting GnRH agonist in the shi drum, Umbrina cirrosa L. (Sciaenidae, Teleostei), a valuable candidate for Mediterranean mariculture

Three experiments of spawning induction in shi drum, Umbrina cirrosa L., were performed in six different commercial Italian hatcheries from May to August (water temperatures: 19–29 °C; salinity: 21–37 p.p.t.). In the first experiment, 119 females (1–4.7 kg), subdivided into 29 lots, were injected with a single dose (2, 5, 8, 10, 15 and 20 μg kg−1 body weight) of short-acting gonadotropin- releasing hormone agonist (GnRHa-S), des-Gly10,[D-Ala6]-LH-RH ethylamide. In the other two experiments, 85 females (0.7–5.8 kg), subdivided into 22 and four lots, were treated with one (40 or 80 μg kg−1) or three doses (40 μg kg−1) of long-acting GnRHa (GnRHa-L), respectively. GnRHa-S stimulated spawning in 69% of the 29 treated lots; the number of eggs laid reached a maximum of 130 000 and a weighted mean of 29 200 total eggs kg−1. GnRHa-L elicited a spawning response in 95% of the 22 one-dose treated lots; the number of laid eggs was higher than with GnRHa-S, reaching a maximum of 213 100 and a weighted mean of 59 400 total eggs kg−1. The yield of developing embryos in 67% of the single GnRHa-L treatments was higher (sometimes up to three times) than with GnRHa-S. Triple treatments of the four lots of females with GnRHa-L always resulted in spawning responses; the best result corresponded to a number of total laid eggs of 358 900 eggs kg−1 with a yield of 177 300 developing embryos.

Spawning induction of three tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana

Tropical sea cucumbers, Holothuria scabra, H. fuscogilva and Actinopyga mauritiana were collected from the wild, held in insulated containers and transported by a combination of sea, air and road transport for up to 12 h. Methods for obtaining reliable supplies of fertilised eggs from wild-caught broodstock were investigated. Of the 779 H. scabra collected, 4.5% eviscerated during transport, compared with 11.0% of the 181 H. fuscogilva and none of the 52 A. mauritiana. Experiments conducted in 20-l containers, with and without sea water and temperature control, determined that H. scabra survived for over 80 h, H. fuscogilva for 8 h and A. mauritiana for 20 h, in static seawater at 29 °C. Spawning of H. scabra in Solomon Islands can be induced throughout the year, but only in 3 months for H. fuscogilva (from August to October), and 2 months for A. mauritiana (from October to November). The peak spawning period for all three species was during the dry season: August–November. Collection, transport and thermal stress was an effective spawning induction method for H. scabra and A. mauritiana. Induced egg production in H. scabra was greatest in September, when 35% of broodstock spawned. Spawning appeared to be entrained to a lunar cycle in H. scabra, and occurred more readily during the afternoon and early evening. Addition of dried Schizochytrium sp. induced spawning in H. fuscogilva and was far more effective than thermal induction. Females of all three species were highly fecund and capable of multiple spawning. The mean number of fertilised eggs was: 1.9 million (±0.6 S.E., n=17) for H. scabra; 2.6 million (±0.2 S.E., n= 5) for H. fuscogilva and 2.6 million (±0.1 S.E., n=6) for A. mauritiana. The techniques for inducing spawning identified in this study allowed the collection of fertilised eggs for experimental and pilot-scale mass production of juvenile sea cucumbers. Further research should target improved spawning induction through the conditioning and holding of captive broodstock.

Spawning induction of individual European sea bass females ( Dicentrarchus labrax) using different GnRHa-delivery systems

The present study evaluated the effect of different delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa) on spawning induction, and egg and larval quality in female European sea bass ( Dicentrarchus labrax). Mature females (mean±S.E.M. oocyte diameter=905±10 μm) were treated with [ d-Ala 6, Pro 9 NEt]-mGnRHa using GnRHa-loaded microspheres, Mc (60 μg kg −1 body weight, bw) GnRHa-loaded implants, EVAc (50 μg kg −1 bw) or received a single injection of GnRHa in saline, IN (15 μg kg −1 bw). Controls (C) were injected with saline. Females were allocated individually in 2-m 3 tanks with two GnRHa-treated males and were allowed to spawn without further handling. All GnRHa treatments induced spawning 3 days after treatment (d.a.t.), whereas control fish did not spawn during the 21-day experimental period. GnRHa microspheres and implants induced up to four consecutive spawns in one female, whereas GnRHa-injected fish spawned only once. Egg quality seemed relatively lower in all GnRHa-treated groups compared to spontaneously spawning fish (natural spawns, NAT group) maintained in large populations (80 fish in 15-m 3 tanks), possibly due to both the isolation of individual females in separate tanks and the stress from handling. Mean egg quality of the first spawns was variable, but similar in all GnRHa treatments (6.6–18.2% buoyancy; 21.7–27.4% hatching). In subsequent spawns, the Mc-treated females produced eggs of higher buoyancy than the EVAc group (20.5±6.0% vs. 2.87±1.14%), and similar to the first spawn of the GnRHa-injected group. Our results indicate that, compared to a single GnRHa injection, GnRHa-loaded microspheres can induce multiple spawns in European sea bass, without a negative effect on egg quality.

Endocrine manipulations of spawning in cultured fish: from hormones to genes

Almost all fish reared in captivity exhibit some form of reproductive dysfunction. In females, there is often failure to undergo final oocyte maturation, ovulation and spawning; while in males milt production may be reduced and of low quality. These dysfunctions are due to the fact that fish in captivity do not experience the conditions of the spawning grounds, and as a result there is a failure of the pituitary to release the maturational gonadotropin, luteinizing hormone (LH). Reproductive hormones have been utilized since the 1930s to stimulate reproductive processes and induce ovulation/spermiation and spawning. The first methods employed freshly ground pituitaries collected from reproductively mature fish, which contained gonadotropins (mainly LH) and induced steroidogenesis and gonadal maturation. Eventually, purified gonadotropins became available, both of piscine and mammalian origin, e.g., carp or salmon gonadotropin, and human chorionic gonadotropin. In the 1970s, spawning induction methods begun employing the newly discovered gonadotropin-releasing hormone (GnRH), which induces the secretion of the fish's own gonadotropin from the pituitary, thereby overcoming the endocrine failure observed in captive broodstocks. Development of highly potent, synthetic agonists of GnRH (GnRHa) constituted the next generation of hormonal manipulation therapies, and created a surge in the use of hormones to control reproductive processes in aquaculture. The most recent development is the incorporation of GnRHa into polymeric sustained-release delivery systems, which release the hormone over a period of days to weeks. These delivery systems alleviate the need for multiple treatments and induce (a) long-term elevation in sperm production and (b) multiple spawning in fish with asynchronous or multiple-batch group-synchronous ovarian physiology. Based on the recent discovery of GnRH multiplicity in fish and the increasing understanding of its functional significance, new GnRH agonists can be designed for more potent, affordable and physiologically-compatible spawning induction therapies. Future strategies for improved spawning manipulations will be based on understanding the captivity-induced alterations in the GnRH system, and on new approaches for their repair at the level of GnRH gene expression and release.

Urophysial and pituitary extracts for spawning induction in teleosts

Several studies have suggested that the caudal neurosecretory system could act on fish reproduction. The aim of this study was to compare the effect of urophysial extract (UE) and carp pituitary homogenate (CPH) on the induction of spawning in Hoplias malabaricus, Rhamdia quelen and Cyprinus carpio. The amount of UE injected was 1.0 to 3.0mg/kg L.W. (single dose) and CPH 3.0 to 4.0mg/kg L.W. (two doses). The application of UE had no effect on spawning induction, while CPH improved spawning of all studied species.

Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina

The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes, well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion.

Reproductive biology of the commercial sea cucumber Holothuria fuscogilva in the Solomon Islands

Reproduction of Holothuria fuscogilva (Selenka, 1867) in the Solomon Islands was investigated over a 4 yr period (1994 to 1998) by macroscopic and microscopic examination of the gonad tubules, the gonad index (GI) method, histological examination of gametogenesis, and spawning-induction trials. The gonad consisted of numerous tubules that dominated the coelom of gravid specimens. New tubules appeared in March, and grew in size and extent of branching until they reached their maximum size and maturity in August. Spawning occurred from August to October, with the majority of gametes released during October, although it was only partial in many individuals. After spawning, the tubules appeared wrinkled and resorbed into the gonad basis. A five-stage gonad maturity scale based on the macroscopic appearance of the gonad tubules corresponded with discrete stages of gametogenesis identified by histology. Gametogenesis was initiated in mid-March, with oogenesis and spermatogenesis occurring in parallel, followed by the growing stage (May to July) which was marked by active gamete development. Successful induction of spawning during the breeding period corroborated the GI and histological data. The uniform growth of gonad tubules indicated that H. fuscogilva in the Solomon Islands does not conform to the progressive tubule recruitment model described for other holothurians. An important application of this study is that the appearance of gonad tubules, removed by biopsy, can be used to determine the gonad condition of wild adults or captive broodstock.

Catechol Concentrations in the Hemolymph of the Scallop, Placopecten magellanicus

Catecholamines have previously been detected in numerous tissues and are thought to control a wide variety of physiological functions in bivalve molluscs. In the present study, alumina extraction and high-performance liquid chromatography reveal the presence of significant concentrations of 3,4-dihydroxyphenylalanine (DOPA), dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) in the hemolymph of the sea scallop, Placopecten magellanicus. The concentration of dopamine in the hemolymph averaged 223.8 ng/ml, (±48.4, SEM), equivalent to 10−7 to 10−6 M. Neither epinephrine nor norepinephrine was reliably detected in significant quantities. Previous studies have demonstrated physiological responses to dopamine with thresholds of 10−9 to 10−6 M, thus suggesting that this catecholamine may have an endocrine function. Furthermore, monitoring hemolymph concentrations of catechols might provide a sensitive measure of the physiological status of bivalves. For example, drugs known to affect catechol concentrations in other tissues also effect hemolymph levels. Administration of monoamine oxidase inhibitors such as pargyline, deprenyl, and clorgyline at 10−4 M for 1 day of incubation followed by a 2-day wash resulted in decreased hemolymph concentrations of DOPAC and increased concentrations of its precursors, DOPA and dopamine. Incubation in 10−4 M 3,5-dinitrocatechol, a catecholamine-O-methyl transferase blocker, for 1 day followed by a 2-day wash significantly increased the concentration of dopamine and DOPAC in the hemolymph. Scallops incubated in 10−5 M α-methyl-p-tyrosine, a blocker of tyrosine hydroxylase, for 1 day followed by a 3-day wash in artificial seawater had significantly reduced concentrations of DOPA, dopamine, and DOPAC in the hemolymph. In addition to responding to pharmacological agents, dopamine levels also decreased significantly following thermal induction of spawning, thus suggesting that hemolymph concentrations of catechols might provide indices of reproductive activity and/or stress.

Interactive effects of diet and temperature on reproductive conditioning of Argopecten purpuratus broodstock

Adult specimens of Argopecten purpuratus, obtained from Culture Centers of Tongoy Bay (Region IV, North of Chile), were conditioned at two temperatures, 16°C and 20°C, and three different diets: a mixture of pure microalgae, microalgae mixed with lipids and microalgae mixed with carbohydrates. Daily food supply was 6% of dry biomass. Three replicate tanks were assayed for each treatment. The progress of gonadal recovery was followed by periodic determination of gonadic index and histological analysis during three months. Gonadal recovery was slower for the animals conditioned at 20°C than for those at 16°C. Recovery was poorest for the animals fed pure microalgae at 20°C. The highest percentages of mature animals, at the end of the experiment, were obtained for the animals conditioned at 16°C and the maximal value was obtained for those fed microalgae–lipids. This diet also rendered the best result for scallops maintained at 20°C. All scallops conditioned at 16°C responded to spawning induction; the poorest response was for individuals conditioned at 20°C and fed pure microalgae. The percentage fertilization of gametes from the different treatment broodstocks did not differ but the percentage of larvae D survival was much higher for those from scallops conditioned at 16°C and fed pure microalgae or microalgae–lipids. These results indicate that temperature affects gametogenesis and that enriched lipid diets may improve the conditioning of bivalve broodstock.

In vivo activity of salmon gonadotropin releasing hormone (GnRH), its agonists with structural modifications at positions 6 and 9, mammalian GnRH agonists and native cGnRH-II on the spawning of an Indian catfish

Effects of the native GnRHs and various agonists have been evaluated on the spawning of an Indian catfish, Heteropneustes fossilis. This study tested salmon (s) GnRH agonists and mammalian (m) GnRH agonists where a D-amino acid residue was substituted alone at position 6 or the C-terminal was modified with ethylamide. GnRH agonists with a combination of these structural modifications were also evaluated separately for their effect on the spawning of the catfish. Native sGnRH, [Pro9 NEt]-sGnRH agonist and chicken (c) GnRH-II exhibited similar activity and induced spawning within 14–18 h at a dose of 100 μg kg−1 body weight (BW). [D-Lys6]-sGnRH agonist and [D-Lys6 Pro9 NEt]-sGnRH agonist, induced spawning at a dose of 100 μg kg−1 BW and 1 μg kg−1 BW, respectively. The most notable observation in this study was the ineffectiveness of [D-Ala6]-mGnRH agonist and [Des Gly10 D-Ala6 Pro9 NEt]-mGnRH agonist. The results obtained suggest that substitution at position 6 alone, and in conjunction with an ethylamide-based modification at the C-terminal in the native sGnRH structure, increases the potency of the tested agonists to induce spawning in the catfish. This study also discusses the potential use and incorporation of cGnRH-II for the development of more generic spawning induction therapies.

Induction and synchronisation of spawning in cultivated turbot ( Scophthalmus maximus L.) broodstock by implantation of a sustained-release GnRH-a pellet

Cultivated turbot were successfully spawned using sustained-release pellets containing a gonadotropin-releasing hormone analogue (GnRH-a), [ d-Ala 6–Pro 9-Net]-luteinising hormone releasing hormone. Significant synchronisation of females was obtained, reducing the spawning season by about half. The number of spawning females was increased, and all sexually mature females ovulated. The delay between ovulations decreased from more than 2 days in controls to about 36 h in GnRH-a treated fish. The mean batch volume increased from 144 to 214 ml, but total volume of eggs for the whole spawning season did not change. At a production scale, fertilisation rate was significantly lower in the GnRH-a group than in the control (76.6 and 89.5%, respectively). Hatching rates were not significantly different between experimental groups.

Effects of temperature and salinity on spawning of the brackish water bivalve Corbicula japonica in Lake Abashiri, Hokkaido, Japan

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 180:213-221 (1999) - doi:10.3354/meps180213 Effects of temperature and salinity on spawning of the brackish water bivalve Corbicula japonica in Lake Abashiri, Hokkaido, Japan Katsuhisa Baba1,*, Masahide Tada2, Toshifumi Kawajiri3, Yasuhiro Kuwahara1 1Hokkaido Abashiri Fisheries Experimental Station, 31 Masuura, Abashiri, Hokkaido, Japan 2Hokkaido Wakkanai Fisheries Experimental Station 4-5-4, Hourai, Wakkanai, Hokkaido, Japan 3Nishiabashiri Fisheries Cooperative Association 330, Yobito, Abashiri, Hokkaido, Japan *E-mail: hf8k-bb@asahi-net.or.jp ABSTRACT: The abundance of planktonic larvae (veliger) of Corbicula japonica in Lake Abashiri, which is near the northern limit of this species' range, was extremely low in 1995 and 1996, compared to other years (1989, 1990, 1994 and 1997). In histological examinations, the female genital tubules were filled with the atretic oocytes after the spawning season of 1995. Therefore, it was concluded that most C. japonica failed to spawn in 1995. The effects of temperature and salinity on the spawning of C. japonica were examined in a spawning induction experiment under laboratory conditions. Probability of spawning by C. japonica in the experiment was described by the equation: 1/{1+exp[-(-15.57+0.57T-12.64S-0.55Ga m+0.69T·S-0.1T·S·Gam)]} (T: temperature, S: salinity, Gam: dummy variable of 1 or 2, i.e. 1 denotes each group to which the gamete suspension was added and 2 each group to which the gamete suspension was not added). The probability of spawning within the group to which the gamete suspension was added (i.e. Gam = 1) explained well both annual and seasonal fluctuations of larval occurrence in Lake Abashiri in past years. The spawning of C. japonica may have been extremely low in 1995 and 1996 because of low temperature and low salinity. Such unfavorable conditions for spawning are not exceptional and occurred in 10 out of 21 years for which data were available. In C. japonica, reproduction succeeds less frequently in northern than in southern populations because the probability of spawning depends markedly on the temperature. KEY WORDS: Temperature · Salinity · Spawning · Corbicula japonica · Atretic oocyte Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Histological classification of oocyte growth and the dynamics of ovarian recrudescence in Tilapia zillii

Serum levels of 17β‐oestradiol and testosterone peaked and fell within 6 days of spawning in Tilapia zillii suggesting that vitellogenic growth began as early as day 2 or 3 postspawning. As early as day 8, stage 6/7 (late nitellogenic and maturing) oocytes occupied 60–70% of the ovary. From day 8 onwards the proportion of stage 6/7 oocytes changed little, though IG increased (as oocytes grew) to reach maximal levels of ∼ 5·5% by day 14. IG was correlated significantly to the proportion of stage 6/7 oocytes. Postovulatory follicles were observed immediately following spawning occupying up to ∼ 7% of the ovary but were not present from day 3 onwards. Atretic oocytes were found throughout the time period monitored (generally occupying <2% of the ovary) but were more prevalent from day 18 onwards. Data suggest that previtellogenic oocytes are recruited into vitellogenic growth immediately after spawning and can complete vitellogenesis as early as day 8 postspawning. Knowledge of this timing is likely to be important in the development of spawning induction programmes in T. zillii and other related species.

Pharmacological characterization of serotonin receptor in the oocyte membrane of bivalve molluscs and its formation during oogenesis

Serotonin (5-hydroxytryptamine, 5-HT) is a major neurotransmitter that triggers the spawning of bivalve molluscs and oocyte germinal vesicle breakdown (GVBD) of oocytes. The present study employed [3H] 5-HT binding assay to characterize a putative receptor on oocyte membranes prepared from scallops and oysters. Results demonstrated a profile of hormone control of 5-HT receptor formation during oocyte growth. The dissociation constants for 5-HT on the surfaces of scallop and oyster oocytes were estimated to be 2.64 μM and 2.01 μM, respectively, and the maximal binding capacity of the oocyte surface was 152 pmol/mg protein in scallops and 529 pmol/mg protein in oysters. The inhibition of [3H] 5-HT bound by various agonists and antagonists provided pharmacological evidence for a 5-HT receptor in each oocyte, a mixed profile of 5-HT1/5-HT2 in scallops and a single profile of 5-HT1 in oyster. Formation of 5-HT receptor on the surface of the scallop oocyte was induced by estradiol-17β(E2), which was suggested as a primary promoter of the effect of E2 on sensitivity to 5-HT, resulting in the induction of spawning. This formation occurred during oocyte growth controlled by E2. J. Exp. Zool. 281:124–131, 1998. © 1998 Wiley-Liss, Inc.

Induction of spawning in gilthead seabream, Sparus aurata L., by a long-acting GnRH agonist and its effects on egg quality and daily timing of spawning

Ovulation and spawning were induced in gilthead seabream, Sparus aurata L., which had failed to spawn spontaneously after thermal manipulations, using a long-acting commercial preparation of leuprolide acetate, an agonist of gonadotropin releasing hormone (GnRHa), in order to study the effects of this treatment on spawning periodicity, the timing of spawning, daily egg production and embryonic viability. Grouped and single females bearing yolky follicles were implanted once with 20, 40 or 80 μg kg −1 (body weight) of GnRHa encapsulated in a biodegradable copolymer, copoly( dl-lactic/glycolic acid ratio of 3:1). All treated females started to spawn after 48 h and about 40% of the eggs were laid during the initial 10-day period with daily peaks of 10 5 eggs kg −1. The mean daily production of viable eggs ranged between 71–288.10 2 eggs kg −1. Embryonic viability was equivalent to that of control fish which were induced to spawn with a rise in water temperature. There was, however, a significantly ( P < 0.01) higher egg production in the GnRHa-treated fish. While egg laying occurred regularly at dawn in controls, the long-acting GnRHa tended to shorten the normal 24-h ovulatory cycle of seabream, gradually shifting spawning from dawn to sunset. In tanks with single females, sudden spawning readjustments were observed from sunset to dawn through short 12-h ovulatory cycles. Interestingly, spawning of single females with two males resulted in a greater percentage of non-fertilized eggs in comparison to groups of spawning females maintained with a similar ratio of males, presumably as a result of territorial competition when few males try to occupy the same spawning tank.

Environmental induction of natural spawning in Gymnarchus niloticus (Cuvier 1829) in an earthen pond

Environmental induction of natural spawning in Gymnarchus niloticus (Cuvier 1829) in an earthen pond

Environmental induction of natural spawning in Gymnarchus niloticus (Cuvier 1829) in an earthen pond

Environmental induction of natural spawning in Gymnarchus niloticus (Cuvier 1829) in an earthen pond

Induced Final Maturation and Spawning of the Marbled Grouper Epinephelus microdon Captured from Spawning Aggregations in the Republic of Palau, Micronesia

AbstractA 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, (&lt;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 &gt;0.6 kg BW, and individuals &gt;1.5 kg BW (46.4 cm TL) were exclusively male. All females with oocytes that averaged (N= 50) &gt;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 &gt;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.

Bioactivity of stored luteinizing hormone-releasing hormone analogue (LHRHa) in sea bass, Lates calcarifer Bloch

The spawning induction activity of dissolved and pelleted (D-Ala6, Pro9 N ethylamide) luteinizing hormone-releasing hormone analogue (LHRHa) stored for various periods was assessed in mature female sea bass. The spawning response of mature fish was reduced significantly after injection of dissolved LHRHa (20 μg kg−1) stored for more than 90 days in a refrigerator (4–10°C) or for more than 30 days at room temperature (28–30°C). Similar to fish administered fresh preparations of LHRHa, fish spawned successfully after injection of a solution of LHRHa previously frozen, subjected to alternate freezing and thawing, exposed to sunlight or implanted pelleted LHRHa (50 ng kg−1) stored at room temperature for 30–120 days. Loss of hormone bioactivity after prolonged storage may have been due to bacterial growth in solubilized preparations. Injection or implantation of stored LHRHa did not influence egg production among treated sea bass. These results demonstrated the relatively prolonged shelf life of stored LHRHa.