Mean Total Fecundity Research Articles

The influence of photoperiod on development and population growth performance of the Phytoseiulus persimilis fed on Tetranychus urticae

ABSTRACT Environmental factors, such as photoperiod, can play an important role in the development of mites. The influence of photoperiod (L:D = 4:20, 8:16, 12:12, 16:8 and 20:4) on the development and population parameters of the predatory mite, Phytoseiulus persimilis Athias-Henriot fed on two-spotted spider mite, Tetranychus urticae Koch was examined under laboratory conditions. Pre-adult development decreased with increasing photoperiod until 12 h, after which the development period progressively increased. Longevity of both sexes demonstrated significant differences throughout photoperiods, with the longest at 20:4 L:D and the shortest at 8:16 L:D. The highest value of mean total fecundity was 13.62 egg/female at 12:12 L:D photoperiod. The net reproductive rate (R 0), the intrinsic rate of increase (r) and the finite rate of increase (λ), showed the highest value at 12:12 L:D. The R 0, r and λ for P. persimilis increased with increasing photoperiod from 4:20 to 12:12 L:D, but decreased sharply at the 16:8 and 20:4 L:D treatments. Our findings indicate that photoperiod has a significant role in advancing the rate of development, survival rate, and reproduction for commercial production of P. persimilis, with a 12:12 photoperiod length recognized as the ideal period for commercial production in culture.

Effects of visible light wavelength on development and demographic parameters of Phytoseiulus persimilis (Acari: Phytoseiidae)

Environmental factors, such as the wavelength of light, can have a crucial impact on mite development. Little is, however, known about the effect of visible light quality on demographic parameters of Phytoseiidae. We therefore conducted series of laboratory experiments in which development and reproduction of Phytoseiulus persimilis Athias-Henriot feeding on Tetranychus urticae Koch eggs was investigated under various light conditions (white, blue, green, yellow, and red light). The results revealed that different light wavelengths influenced each developmental stage, with the green light conditions promoting longest pre-adult development. The longevity of both male and female mites varied significantly across light wavelengths, with the shortest lifespan observed under red light. The highest mean total fecundity, 16 eggs per female, was observed under white light conditions. Population parameters (R0, r, and λ) were also highest under white light and decreased with increasing light wavelength. These findings suggest that light wavelength plays a significant role in development, survival, and reproduction of the predatory mite, with white light being identified as providing the best light conditions for commercial production of P. persimilis.

Unveiling growth and reproduction of a giant Patagonian galaxiid: an experimental rearing study

ABSTRACT Understanding the life history of understudied native and threatened fishes is crucial to develop conservation strategies for freshwater ecosystems. Puye grande (Galaxias platei) is an endemic freshwater fish of Patagonia with little known about its life history traits. To bridge this information gap, comprehensive studies under controlled conditions could expand our basal understanding of puye grande’s life history. We conducted a long-term experimental study using one cohort of puye grande throughout its lifespan. We collected 423 postlarvae individuals from the Riñihue Lake (southern Chile) and reared them for 11 years under captivity. We documented the maximum longevity of this species as 11 years, with a survival rate of 0.47% for the entire study period. Hatchery-reared individuals showed isometric growth (b = 2.75). Parameters of the von Bertalanffy growth model were asymptotic total length L ∞ = 20.80 cm, growth coefficient K = 0.75 yr−1, and theoretical age at-length zero t 0 = 0.45 yr, including both sexes. Puye grande showed an iteroparous life history, with the first spawning event occurring at age 2+ and consecutive spawning events occurring mainly in fall and winter. Females had a mean (standard deviation) total fecundity of up to 58 500 (23 331) eggs individual−1 and a mean relative fecundity in fall of 621 (109) eggs g−1 wet mass; males had a mean spermatic density of 28.41 (4.18) × 109 spermatozoa mL−1. The embryonic development until eclosion occurred 432 h post fertilization (hpf) at 12 °C. Our valuable baseline findings about the life history of puye grande can contribute to future strategies for managing and conserving galaxiids under global environmental change in Patagonia.

Mackerel (Scomber australasicus) Reproduction in Northeastern Taiwan

Blue mackerel (Scomber australasicus) is a crucial target species for coastal fisheries in Taiwan, and additionally it has maintained its status as the highest-produced species. The timely measurement of spawning status is crucial for determining the correct management strategy for this species. The objective of this study was to determine size at maturity, fecundity, batch fecundity, and spawning frequency on the basis of samples collected from Nan-Fang-Ao fishing port in Yilan, during the spawning season from 2017 to 2019. Histological sections indicated that the blue mackerel were multiple spawners; a higher percentage of female fish spawned at the peak of the gonadosomatic index. The 50% sizes at maturity were 32.02, 32.13, and 29.64 cm. Mean total fecundity (batch fecundity) was 165 (103), 229 (96), and 210 (68) oocytes per ovary-free weight (g) for 2017, 2018, and 2019, respectively; fecundity was determined through observation of postovulatory follicles (POFs). The spawning frequencies (spawning fraction) in 2017, 2018, and 2019 were 3–10 days (0.13), 4–14 days (0.08), and 4–12 days (0.09), respectively. The spawning frequencies determined through the three estimated methods, namely the sums of (a) hydrated and Day 0 POFs; (b) Day 1+ POFs, and (c) all data combined, were 1 spawning event per 8, 10, and 9 days, respectively. The reproduction of the blue mackerel was greater in 2017 than it was in 2018 or 2019, as indicated by the higher batch fecundity and shorter spawning seasons. Environmental factors should also be considered as a major factor influencing successful reproduction and spawning season

Parasitoid age and host age interact to improve life history parameters and rearing of Trichogramma euproctidis

ABSTRACT Trichogramma euproctidis (Girault) is an egg parasitoid under consideration for mass production and augmentative biological control of major lepidopteran pests in Iran and other countries. The main objective of this research was to determine the effects of T. euproctidis female age and Ephestia kuehniella Zeller egg age on life history parameters of T. euproctidis. Experimental design involved exposing 1-, 2-, 3-, or 4-d-old E. kuehniella eggs to 1-, 2-, 3-, or 4-d-old T. euproctidis females in glass test tubes. Results indicated that host egg age and parasitoid female age interacted significantly to improve parasitism rate, progeny emergence rate, sex ratio, longevity, and fecundity of T. euproctidis. The age of T. euproctidis females affected parasitism rate; 1-d-old females, rather than the other ages, parasitised more E. kuehniella eggs. The highest mean total fecundity (81.62 eggs) was recorded from adult progeny produced by 1-d-old T. euproctidis females reared from 1-d-old E. kuehniella eggs. Trichogramma euproctidis development time increased as the age of E. kuehniella eggs increased, but the parasitoid female age and host egg age interaction was not significant. A life table analysis confirmed the results that 1-d-old T. euproctidis females and 1-d-old E. kuehniella eggs resulted in optimal effects on T. euproctidis life history. This study implies that mass rearing systems designed to expose young-aged T. euproctidis females to young-aged E. kuehniella eggs would maximise T. euproctidis progeny production.

Biological Parameters of the Bark Beetle, Xylosandrus crassiusculus (Motschulsky) Under Controlled Laboratory Conditions

Biological parameters of the bark beetle, Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae: Scolytinae) was investigated under different temperature regimes (27, 29, 31 and 35ºC). The females reared at 29°C, lived 30.93±2.36 days for oviposition. The female laid a maximum of 6.71±1.89 eggs per day and a maximum of 6.99±1.33 batches per female. Each batch had an average of 13.78±2.01 eggs. The mean total fecundity recorded was 67.8±4.25 eggs, with a shortest egg incubation period. At 29°C, the duration of the larval stage was 20.17±2.89 days, the pupal stage 5.03±1.11 days, and the life span of the adult insect was 29.44±3.19 days. Significant differences (P<0.05) were noted when the duration of the different life stages under 29 and 35ºC were compared, with longer duration at 29°C. Insects reared at 35°C had narrower bodies and smaller sizes. Furthermore, the developmental stages period, including the ovipositional period (days) were negatively correlated with temperature. Keywords: Xylosandrus crassiusculus, bark beetle, biological parameters, temperature regimes.

Reproductive biology of the anchovy (Stolephorus commersonnii, Lacepède, 1803) and spotted sardine (Amblygaster sirm, Walbaum, 1792) from Tanga Region, Tanzania

The present study investigated the reproductive biology of Stolephorus commersonnii and Amblygaster sirm at two landing sites in Tanga on the northern coast of Tanzania. Fish samples were collected on a monthly basis from ringnets operated by artisanal fishers in the nearby coastal waters. Spawning seasons were determined using gonadosomatic index (GSI) and gonadal maturity stages. The size at first maturity was 57.7 mm and 66.2 mm total length for male and female S. commersonnii respectively. Male and female A. sirm were estimated to attain first maturity at 147.7 mm and 169.2 mm respectively. The spawning seasons of both species were protracted. S. commersonnii demonstrated a year round spawning cycle with peaks in August, October and January. The peak spawning season for male and female A. sirm was recorded in August and September respectively. Both species exhibited skewed size-dependent sex ratios with females predominating in the larger size classes. A. sirm had a higher fecundity rate with a maximum of 96,500 eggs in the largest female fish of 258 mm as compared to S. commersonnii (10,055 eggs) in the largest fish of 98 mm. The mean (±SE) total fecundity of S. comersonnii and A. sirm was 5,134.7 ± 136.9 eggs, and 47,029.03 ± 1,435.13 eggs in females of sizes 68 mm to 98 mm and 170 mm to 258 mm respectively.

Optimization of a GnRHa treatment for spawning commercially reared greater amberjack Seriola dumerili: Dose response and extent of the reproductive season

Reproduction control has been one of the main bottlenecks for the commercialization of greater amberjack Seriola dumerili, a promising species worldwide due to its rapid growth, large size and high market acceptability. Oocyte maturation, ovulation and spawning has been recently controlled successfully in a number of studies using hormonal therapies in the form of controlled-release delivery systems of Gonadotropin Releasing Hormone agonists (GnRHa). The objectives of the present optimization study were (a) to determine the most efficient GnRHa implant dose and (b) to examine the extent of the spawning induction period in greater amberjack reared in sea cages throughout the year, based on the resulting spawning kinetics, egg production and quality. Wild-caught greater amberjack were maintained in two commercial facilities, and were transferred to onshore tanks for spawning after treatment with GnRHa implants (a) of different doses (25 and 75 μg kg−1 body weight), or (b) at different times during the expected spawning season (June–July). Both doses were equally effective, and two consecutive implantations in 2 weeks resulted in mean (±SD) total relative fecundity of 185,221 ± 91,311 to 199,492 ± 16,973 eggs kg −1 in 11–18 spawns, without any significant differences in egg quality. Breeders maintained in sea cages were taken at different times and were induced to spawn successfully with a GnRHa implant of a recommended dose of 50 μg kg−1, during an effective period of at least 2 months when seawater temperature was 19–24 °C. The obtained information will contribute further to the delivery of an efficient egg production protocol to the aquaculture industry of the greater amberjack.

Effects of Host Blood on Fecundity and Longevity of Female Anopheles Mosquitoes

Aim: The effect of Host blood on the fecundity of female Anopheles gambiae sensu lato mosquitoes was studied under normal conditions of 64±2% Relative Humidity and 27±2ºC Temperature.
 Methods: Three-five day old (F1) female Anopheles mosquitoes were transferred into wooden cages (40x40x40 cm) and fed blood from the following sources: man, cattle, chicken, goat, pig and sheep through an artificial feeding membrane. Engorged females were observed and fecundity recorded. The entire experiment was replicated five (5) times.
 Results: From the 1st to 4th gonotropic cycle, mosquitoes fed human blood produced significantly greater (p<0.05) number of eggs (Mean=121.90±1.18, 101.36±1.56, 64.12±1.54 and 29.66±1.69 respectively) than mosquitoes fed other blood meal sources. Across the six (6) blood meal trials (excluding that of sheep), there was a significant reduction (p<0.05) in fecundity from the 1st to 4th gonotropic cycles (1st>2nd>3rd>4th). There was no significant difference (p>0.05) in fecundity between pigs, chicken and sheep. Total mean longevity and total mean fecundity was significantly greater (p<0.05) in mosquitoes fed human and cattle blood than in mosquitoes fed the other blood sources.
 Conclusion: The results showed that blood meal source affects fecundity and longevity of female Anopheles gambiae s. l mosquitoes reared under laboratory conditions and that blood from humans as well as from other domestic animals is suitable for sustaining vectorial capacity in Anopheles gambiae s. l mosquitoes.

Sıddıklı Barajı’nda Yaşayan Yayın Balığı (Silurus glanis, L., 1758)’nın Üreme Özellikleri

In this study, some reproduction properties (sex ratio, reproduction period, egg diameter and fecundity) of Silurus glanis inhabiting Sıddıklı Reservoir were investigated. A total of 200 samples were caught between September 2015 and August 2016 from different regions of Sıddıklı Reservoir. Sex ratio was calculated as 0.88:1.00 (Female: Male). The sex ratio was not statistically different from the expected 1.00:1.00 (χ2= 0.841, P>0.05). The values of gonadosomatic index (GSI) varied from 0.033 to 11.80 in females and 0.008 to 0.451 in males. According to GSI values, reproduction period of the S. glanis in Sıddıklı Reservoir was determined to be between April and June. The mean total fecundity and egg diameter were calculated as 46343 eggs/individual and 1.758 mm, respectively. Relative fecundity for each kilogram of female fish was 13000 eggs. The strong relationships between total fecundity-length and total fecundity-weight were determined (r2>0.80).

Temperature-dependent development and oviposition models of Leptocorisa chinensis Dallas (Hemiptera: Alydidae)

Leptocorisa chinensis Dallas (Hemiptera: Alydidae) is known to cause pecky rice by sucking panicles of milk stage of rice. Based on its continuous spread and expanded damage area in Asian countries such as Japan with high reproduction potential, it is highly likely that L. chinensis will become an important rice pest in the near future. However, limited information is available to predict its distribution and occurrence. Thus, the objective of this study was to develop models for their development and oviposition. We investigated the development of L. chinensis immatures (from egg to adult) at 11 constant temperatures ranging from 16.2 to 35.3°C and the oviposition of female adults at five constant temperatures ranging from 22.3 to 35.3°C in this study. For L. chinensis immatures, the lower developmental threshold temperature, optimal developmental temperature, upper developmental threshold temperature were 12.7, 32.3, and 37.6°C, respectively. The highest survival rate of immatures was observed at temperature of 25.2°C and the highest mean total fecundity was 585.8 at 28.0°C. This study provides basic information for the ecology of L. chinensis. It is applicable to forecast the phenology of its populations in the fields and to predict its future distribution under global warming.

Effect of temperature on longevity and fecundity of Phyllonorycter ringoniella (Lepidoptera: Gracillariidae) and its oviposition model

Asiatic apple leafminer, Phyllonorycter ringoniella, is an important insect pest in apple orchards. However, information on its temperature-dependent reproductive behavior and oviposition model is lacking. The longevity and fecundity of P. ringoniella were investigated at seven constant temperatures (13.7, 15.6, 20.5, 23.7, 26.1, 30.2, and 32.3°C), 60–80% RH, and a photoperiod of 14:10 (L:D) h. The longevity and fecundity of P. ringoniella were significantly influenced by temperature. Female adult longevity ranged from 6.3days at 32.3°C to 18.3days at 15.6°C. The fecundity ranged from 9.9 eggs at 32.3°C to 65.2 eggs at 15.6°C. The preoviposition (1.5–4.1days) and oviposition (1.8–12.6days) periods were significantly affected by temperature, while the postoviposition (1.2–2.2days) period was not. Female adult aging rates (1/mean longevity) were well described by an inverse second-order polynomial function (r2=0.98), which was used to calculate the physiological ages of female adults. The oviposition model of P. ringoniella comprised four components: adult aging rate model, total fecundity model, age-specific oviposition rate model, and age-specific survival rate model. The relationship between mean total fecundity and temperature was well described by an extreme value function (r2=0.95). Age-specific cumulative oviposition rate was well fitted to a three-parameter Weibull function (r2=0.98) and age-specific survival rate to a sigmoid function (r2=0.99), respectively. The model would be useful in predicting egg occurrence of P. ringoniella and establishing a management strategy against P. ringoniella in apple orchards.

Communal pair spawning behaviour of vendace (Coregonus albula) in the dark

AbstractMating in nature is rarely random, and most fish species have refined mating systems. The vendace (Coregonus albula) is a short‐lived, small‐sized, cold‐water‐adapted pelagic schooling species that is known to spawn in groups, but the actual mating system of this species, like many other group‐spawning fishes, has not been described in detail. Vendace typically spawn in the littoral or sublittoral zones of lakes in late autumn, and the hatching of larvae occurs close to icebreak in the following spring. In our large study lake, vendace larvae were caught in 93% of 1,149 random sampling locations lake‐wide. We examined the courtship and mating of vendace under experimental conditions by nonintrusive observation of the natural behaviour, to clarify whether spawning activity is associated with illumination and to assess the postspawning mortality of vendace. Here, we describe and document in detail for the first time the spawning behaviour of vendace: they spawn in the dark, and females release a small portion of their eggs (on average 1% of mean total individual fecundity) when the female and male, side by side, dart from near the bottom up towards the surface, that is perform a spawning rise. Males and females had several spawning rises (on average 1,200). Our results showed high postspawning mortality (56%). The spawning stress seems to be a potential component of mortality regulating the lifespan duration of vendace.

Enhancement of oogenesis/spermatogenesis in meagre Argyrosomus regius using a combination of temperature control and GnRHa treatments

A multiple GnRHa injection method for inducing spawning of high fecundity and quality in meagre was optimized. Specifically, the study (a) examined how long females would continue spawning in response to consecutive, weekly GnRHa injections, if maintained at the natural spawning temperature, and (b) evaluated whether males can produce adequate amounts of good quality sperm for the same period, with the assistance of a GnRHa therapy. Combined with stable temperatures (19–20°C) that are prevalent during the early spawning season (April–May) in the Mediterranean Sea, each weekly GnRHa injection induced ~2 consecutive spawns per week for a period of 17weeks. Fish spawned consistently 2days after treatment and produced high fecundity and egg quality (i.e. fertilization, hatching and early larval development). Maximum mean total fecundity (±S.D.) obtained was 1,415,000±149,000eggskg−1 in 32 spawns, being the highest total season fecundity reported for meagre, and significantly higher than the estimated maximum potential fecundity for the species. At the same time, sperm of consistently high quality (i.e. initial motility, duration of motility and storage survival) was produced in response to treatment with multiple GnRHa implants, though towards the end of the experiment a significant reduction (ANOVA, P≤0.05) in spermatozoa density was observed. This protocol is expected to enhance greatly commercial production of meagre. Statement of relevanceThe present study reports on an optimized protocol for the induction of consistent and repeated spawning in meagre, based on the use of weekly GnRHa injections combined with stable temperatures that are prevalent at the early spawning season in the Mediterranean Sea. This protocol produced eggs of high fecundity and quality (i.e. fertilization, hatching and early larval development) for a period of >4months, and it is expected to enhance greatly commercial production of meagre.

Performance of Five Species of Phytoseiid Mites (Acari: Phytoseiidae) on Bactrocera zonata Eggs (Diptera: Tephritidae) as a Factitious Food

Development, survival and reproduction of the generalist predatory mites, Amblyseius largoensis (Muma), Neoseiulus barkeri (Hughes), Typhlodromips swirskii (Athias-Henriot), Proprioseiopsis kadii (El-Halawany and Abdel-Samad) and Cydnosus negevi (Swirski and Amitai) were assessed when fed on eggs of Bactrocera zonata (Saunders) (Diptera: Tephritidae) as a factitious food. For N. barkeri and P. kadii, the development was faster, while the reproduction was higher in N. barkeri and A. largoensis than for P. kadii. Survival of immatures of T. swirskii and C. negevi was low on eggs of B. zonata and all failed to develop beyond the protonymphal stage. A total of 35.4, 31.2 and 19.6 eggs per female, respectively, were obtained when N. barkeri, A. largoensis and P. kadii were fed B. zonata eggs. A diet of the peach fruit fly eggs provided the longest female longevity and highest mean total fecundity, which resulted in the highest net reproductive rate (Ro=34.61 and 32.78) and doubling time (DT=1.53 and 1.60) for N. barkeri and A. largoensis, respectively.

Influence of temperature on the development, reproduction, and life table of Calliptamus italicus (L.) (Orthoptera: Acridoidea)

Calliptamus italicus is a migratory species of grasshopper that can cause serious damage to grasslands in Xinjiang, China. In this study, we examined the effects of different temperatures (23, 26, 29, 32, and 35°C) on the lifecycle and life table parameters. The results showed that temperature strongly influences the growth and development of C. italicus. At temperatures ranging from 23 to 35°C, the development time was negatively linearly related to temperature (P<0.01). The time of development from an egg to an adult (pre-oviposition) ranged from 86.8d at 26°C to 40.6d at 35°C, and no oviposition occurred at 23°C. An average of 687.1degree-days was required for complete development to occur above the lower threshold temperature (18.3°C). Egg hatching rates and nymph and pre-adult survival rates were lowest at 23°C (95.6%, 72.6%, and 0%, respectively) and highest at 32°C (97.8%, 86.2%, and 88.7%, respectively). The mean total fecundity ranged from 41 eggs/female at 26°C to 55 eggs/female at 32°C. The sex ratio (% females) ranged from 30 to 52%. The intrinsic rate of population increase (rm) at the different temperatures ranged from 0.0020 to 0.0447d−1, with the highest value recorded at 32°C. These results indicate that temperature significantly affects the biology of C. italicus and that the optimal temperature range for its development is 26–32°C.

Growth and reproduction of a marine fish, Atherina boyeri (Risso 1810),in a freshwater ecosystem

Atherina boyeri (Risso, 1810) has established abundant and successful populations in inland waters in Anatolia, although it is known as a marine species. In this study, the growth and reproduction properties of A. boyeri in the Hirfanli Reservoir were studied. Age determinations based on scale readings showed that the population had a 4-year life cycle. Sampled individuals ranged between 5.76 and 115.65 mm in total length and 0.01 and 10.48 g in total weight. The von Bertalanffy growth parameters for females were L∞ = 156.78, k = 0.197, and t0 = ?0.197; for males, L∞ = 151.02, k = 0.148, and t0 = ?0.148. Mean condition factor values, estimated from eviscerated weight, varied between 0.49 and 0.60. The length weight relationship of A. boyeri indicated allometric growth, whereas the b value for females, males, and juveniles was 3.29, 3.23, and 3.50, respectively. The sex ratio was 1:1.14 in favor of females. The reproductive season, evaluated by the gonadosomatic index, extended from May to July. Mature egg diameter ranged from 0.64 to 1.73 mm. The mean total fecundity increased with age. In the Hirfanli Reservoir, certain life-history features of A. boyeri, such as short life cycle and increasing fecundity, indicated that this species has the potential to become dominant in freshwater systems.

Response of endemic Clarias species’ life-history biometrics to land use around the papyrus-dominated Mpologoma riverine wetland, Uganda

The Mpologoma River wetland is highly negatively impacted by rice growing and yet it provides habitat to endemic Clarias species that are important to the wetland fishery. Variations in life-history biometrics of small Clarias species at various wetland sites in relation to land-use changes within the wetland were studied in 2012. Four sites exposed to different land uses were sampled for vegetation, water quality and small Clarias species’ life-history biometrics. Water conductivity was significantly higher at the highly disturbed site, ranging from 140 to 480 µS cm−1. Limiting nutrient levels, particularly phosphorus, were higher at the least disturbed sites. Two small Clarias species were identified. Mean total length and weight of Clarias liocephalus, the most abundant species (66%), were 16.81 cm (SD 4.03) and 33.77 g (SD 19.63), respectively, whilst those for Clarias alluaudi (34%) were 17.83 cm (SD 4.49) and 39.94 g (SD 22.99), respectively. Mean total length, weight and fecundity of both species were significantly higher at the highly disturbed sites than at the least disturbed sites. Habitat disturbance intensities due to land use conferred population-level benefits such as higher values of life-history biometrics of Clarias species at the highly disturbed sites in the wetland.

Growth and reproduction of a stream population of Cobitis turcica in central Anatolia (Turkey)

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Reproduction of hatchery-produced meagre Argyrosomus regius in captivity II. Hormonal induction of spawning and monitoring of spawning kinetics, egg production and egg quality

The present study aimed at the development of an effective and efficient hormonal spawning induction method for meagre Argyrosomus regius, using controlled-release delivery systems loaded with gonadotropin-releasing hormone agonist (GnRHa). Three sets of spawning induction experiments were undertaken in the course of three years. In experiment 1, group spawnings were performed at different times during the reproductive period, in order to determine the most appropriate time for hormonal induction of spawning. Experiment 2 described in more detail the spawning kinetics of individual females induced to spawn at different times during the season, in order to obtain important information on spawning kinetics, batch fecundity and total fecundity in response to the hormonal treatment. In experiment 3, two similar broodstocks were used to obtain further production characteristics and monitor variations in egg/larval quality over the spawning period. The effective GnRHa doses used were 55–84μgGnRHakg−1 body weight in males and 46–92μgGnRHakg−1 in females. In general, successful spawning induction was achieved between early May and early June. Implantation with GnRHa induced spawning 2–3d after treatment and produced an average (±SD) of 12±5 spawns per broodstock or female over 3weeks, most of them over consecutive days. Batch fecundity was extremely variable (mean of 6631 to 104,409eggskg−1), with the largest batches occurring 3–4d after treatment, and very low fecundity after 1week from GnRHa treatment. As a result, the first 4 spawns of all spawning induction experiments constituted a mean of 75±13% of the total relative fecundity. Overall mean total relative fecundity was variable at 380,780±167,577eggskg−1. Evaluation of the ovaries after the cessation of spawning, demonstrated that the females still contained large numbers of oocytes in full vitellogenesis, and it is hypothesized that these fish could spawn further in response to a second GnRHa implantation. Fertilization success was very high in all spawning induction experiments, with the overall mean being 89±5%. Similarly, the produced eggs were of very high quality, based on the survival of the eggs during embryogenesis (>95%), hatching success (>99%) and larval survival 5d after egg collection (>87%), resulting in an overall larva survival of 73% of the total number of eggs spawned. These studies demonstrate that the GnRHa implants are an effective and efficient method for the induction of spawning in meagre, leading to the production of eggs of high fecundity and quality.