Effects of Maternal Age on Fecundity,Spawning Interval,and Egg Quality of Nile tilapia,Oreochromis niloticus (L.)

Effects of maternal age on fecundity, spawning interval, and egg quality of Nile tilapia, Oreochromis niloticus (L.), was examined for four age groups (4, 9, 16, and 24 mo) in circular concrete tanks in a recirculating system. Fecundity (eggs per spawn), weight (g), and egg quality were monitored every 4 d for the 168‐d experimental period. Eggs per spawn correlated with maternal age, while it did not correlate with body weight. Eggs per spawn increased by twofold between 4‐ and 24‐mo‐old females, while eggs per female per d did not differ. Implying that eggs per female per d was influenced by spawn per female as well. Eggs per female per d was 1.8 and 2.4 times higher in 9‐mo‐old females than 16‐ and 24‐mo‐old females, respectively. Eggs per female per d showed a decline concurrent with per spawn per female trend after 18‐mo old. Four‐mo‐old females produced eggs that were more uniform in size and weight than others. While egg size (mm) and weight (mg), and their variations within eggs per spawn increased, percent fertilization and hatchability decreased with age of females. Biological optimum age range for reproducible production of good quality eggs was 6–18 mo. This could be adopted in selecting breeders for better seed production.     

Spawning Characteristics of the South African Mudcrab Scylla serrata (Forskål) in Captivity

Scylla serrata is a potential aquaculture species in Southern Africa. Information about its reproductive biology is required as a prerequisite to establishing hatchery technology. Adult female S. serrata were caught in the Umlalazi estuary on the subtropical east coast of South Africa and kept in captivity to observe and record spawning characteristics. Data collected included crab size and mass, time in captivity prior to spawning, fecundity per batch, relative fecundity, individual egg mass and size, size of zoea 1 larvae, incubation time, and hatch success rate. Of the 119 crabs kept in captivity 83% spawned in the maturation system– most within 40 d of capture. The crabs were highly fecund (mean relative fecundity per batch = 10,655 ± 4,069 eggs/g female) and the majority of the batches hatched within 288 h (12 d) at 27 C. Spawning in captivity occurred throughout the year, with a peak in late winter/early spring. This differs slightly from records of ovarian maturity stages of the crabs in the wild. A pattern of synchronous spawning was recorded where the females were observed to extrude their eggs in groups, commonly within 3 d of one another, separated by long periods of inactivity, suggesting an exogenous spawning cue. A total of 1,374,488 zoea larvae were obtained per kg of female per month. This means that if sufficient mature females can be caught from the wild, these could be used for stocking hatchery operations. The crabs were easy to maintain, mature, and spawn in captivity. This will facilitate future domestication which will eventually reduce the need for wild caught broodstock. The spawning characteristics of South African 5. serrata At in well with those observed for the genus throughout its distribution implying that ecological and fisheries management could be similar.     

Effect of number of spawns on the resulting spawn quality of 1-year-old pond-reared Penaeus vannamei (Boone) broodstock

For production of shrimp larvae in a commercial hatchery, multiple spawning of females is highly desirable, provided spawn quality is not affected. Using biochemical and production approaches, 349 females were individually followed, and 69 spawns were sampled over a 3‐month period. The quantity of eggs and nauplii per spawn was greater in females with multiple spawns. Several indicators of spawn quality, such as fertilization and hatching rates, per cent of viable spawns, and morphometric characteristics of eggs and nauplii were not affected by consecutive spawns. Analyses of egg and nauplii biochemical composition indicate that adequate transfer of nutrients to eggs is not compromised with successive rematurations and spawnings. Strategies that focus on the selection of shrimp with multiple spawning capacities could be a promising approach to increasing larvae production.     

Zero-Inflated Discrete Statistical Models for Fecundity Data Analysis in Channel Catfish, Ictalurus punctatus

Traditional fecundity analysis, either as number of eggs per body weight of female or number of eggs per gram of egg mass, pay little attention to females that do not spawn. These fecundity variables contain a high proportion of zeroes either because of the absence of eggs or the inability to recover the eggs. Zero‐inflated discrete generalized linear models are an alternative method that can be developed to take into account females that do not spawn. In this case study, we propose discrete generalized linear models that use specially constructed mixture models to handle the excess zeroes such as the zero‐inflated Poisson and zero‐inflated negative binomial models. These models have the advantage of modeling fecundity simultaneously with the probability of spawning. The results show that age was the most significant factor influencing the number of eggs per gram of egg mass, while period of spawning was the most significant factor influencing the number of eggs per female body weight. These were also the most important variables that significantly affected the probability of successful spawning. Model residual diagnostics show that zero‐inflated models exhibit superior performance compared to the traditional models like analysis of covariance, Poisson regression, and negative binomial regression models.     

Oogenesis and relevant changes in egg quality of abalone Haliotis discus hannai during a single spawning season

Oogenesis of abalone Haliotis discus hannai was examined histologically during a single spawning season using broodstock of various maturation conditions, which were controlled by effective accumulative temperature (EAT). The quality of eggs spawned was determined in relation to oogenesis. For histological examinations, three to five females were sacrificed at 300, 600, 850, 1050, and 1150 °C days EAT, without induction of artificial spawning. Other females were successfully induced to spawn at 700 °C days EAT and were reared following spawning. Three of these females were then sacrificed every 200 °C days EAT until 1300 °C days EAT. Gonad histology showed that two oocyte cohorts matured in H. discus hannai ovaries during a single spawning season. One mature oocyte cohort could be spawned in multiple times. The second oocyte cohort started developing after the first oocyte cohort had been spawned or reabsorbed, and became fully mature 400 °C days EAT after the first cohort was depleted. For egg quality measurements, three to five females were successfully induced to spawn at 850, 1050, 1150, 1900, and 2350 °C days EAT (Experiment 1). Three females were induced to spawn twice, at 700 and 1500 °C days EAT, resulting in two batches of eggs from the same individuals (Experiment 2). Total lipid and protein content of eggs were measured and were greater in eggs from the second cohort than in eggs from the first cohort. No carbohydrates were detected in eggs and there was no difference in cytoplasm volume between the two cohorts. In hatcheries producing H. discus hannai, it is important to increase post-larval starvation tolerance by increasing the quality of eggs, to yield higher and more consistent survival. The results of this study suggest that H. discus hannai hatcheries should use eggs from the second oocyte cohort, which are of higher quality, rather than eggs from the first oocyte cohort.     

Voluntary Spawning of Captive Nassau Groupers Epinephelus striatus in a Concrete Raceway

Nassau groupers Epinephelus striatus held in a 37-m³ concrete raceway were conditioned to spawn 3 mo later than in their home waters. After being held in the raceway for 15 mo, four female and two male groupers spawned voluntarily over a 4-d period in March 1994, producing 10.3 million eggs. By December 1994, two females had been removed. During March 1995, one of the remaining two females spawned on three consecutive days (60 cm TL, 1,172,000 eggs) and the other only on the third day (47 cm TL, 488,000 eggs). In April 1995, three females (including one held in isolation for 6 mo, then replaced 6 d before the first spawn) produced more than 9.8 million eggs in 4 d. The isolated female spawned 8 d after being placed in a cage in the raceway and 4 d after release in the raceway.
Individual females spawned as many as nine times a day for 1–4 d. Spawning occurred from 3.5 d before until 8.5 d after the full moon. A 30-d interval elapsed between March and April 1995 spawning periods. Fertilization was in the range 83–100% and hatching 90–100%. Spawns occurred in a temperature range of 23.1–27.9 C; however, based on spawning frequency and volume and on egg development, 24–27 C seems most suitable. These results and other evidence support the view that Nassau groupers can be conditioned to spawn any month of the year, mainly by manipulating temperature.     

Small-scale fry production systems for Nile tilapia, Oreochromis niloticus (L.)

Abstract Experiments were conducted to evaluate and compare the production, quality and survival of eggs and the subsequent growth and survival of fry in two small-scale production systems: natural incubation and egg collection followed by artificial incubation. Artificial incubation produced a significantly greater number and biomass of fry per unit weight of female broodstock (P < 0·05). This was due to the significantly decreased spawning interval in females from which eggs were collected (mean = 23· days) compared to naturally incubating females (mean = 36·8 days). It is also hypothesized that survival during artificial incubation (85%) is greater than in natural incubation. Cost-benefit analysis demonstrated a threefold increase in total net returns for artificial incubation.     

Energy acquisition and allocation to egg production in relation to fish reproductive strategies

Oogenesis in fishes follows a universal plan; yet, due to differences in the synchrony and rate of egg development, spawning frequency varies from daily to once in a lifetime. Some species spawn and feed in separate areas, during different seasons, by storing energy and drawing on it later for reproduction (i.e. capital breeding). Other species spawn using energy acquired locally, throughout a prolonged spawning season, allocating energy directly to reproduction (i.e. income breeding). Capital breeders tend to ovulate all at once and are more likely to be distributed at boreal latitudes. Income breeding allows small fish to overcome allometric constraints on egg production. Income breeders can recover more quickly when good‐feeding conditions are re‐established, which is a benefit to adults regarding bet‐hedging spawning strategies. Many species exhibit mixed capital‐ and income‐breeding patterns. An individual's position along this capital–income continuum may shift with ontogeny or in relation to environmental conditions, so breeding patterns are a conditional reproductive strategy. Poor‐feeding environments can lead to delayed maturation, skipped spawning, fewer spawning events per season or fewer eggs produced per event. In a few cases, variations in feeding environments appear to affect recruitment variability. These flexible processes of energy acquisition and allocation allow females to prioritize their own condition over their propagules' condition at any given spawning opportunity, thereby investing energy cautiously to maximize lifetime reproductive value. These findings have implications for temporal and spatial sampling designs, for measurement and interpretation of fecundity, and for interpreting fishery and ecosystem assessments.     

Biofloc technology in intensive broodstock farming of the pink shrimp Farfantepenaeus duorarum: spawning performance,biochemical composition and fatty acid profile of eggs

A 45‐day trial was performed to evaluate the effect of biofloc technology (BFT) with or without fresh food (FF) supplementation during pre‐maturation period on Farfantepenaeus duorarum spawning performance, biochemical composition and fatty acid profile of eggs as compared with conventional clear‐water system (CW+FF). Females raised in biofloc and that received FF supplementation (FLOC+FF) achieved better spawning performance in terms of number of eggs per spawn (49 × 10³), number of eggs per spawn per g of spawner's body weight (2.1 × 10³) and egg size (~275 μm) as compared with CW+FF (23 × 10³, 1.1 × 10³ and 263 μm respectively), but both treatments did not vary from FLOC (P > 0.05). High spawning activity was also observed in biofloc system as compared with clear‐water system as shown in number of spawns per ablated female (2.2–3.0 versus 0.6) and percentage of females that spawn at least once (80–82 versus 25%). Biochemical composition of eggs presented no significant differences among treatments. FA profile of eggs indicated that high spawning activity performed by females in FLOC+FF treatment was reflected in lower mean levels of EPA, DHA and sum of polyunsaturated fatty acids (n‐3) and (n‐6). The better reproductive performance demonstrated by females raised in biofloc justified the application of this technology in F. duorarum broodstock.     

Effect of density on brood size in noble crayfish,Astacus astacus L., subjected to indoor rearing conditions*

Abstract. The effects of density, cover, and individual versus communal holding on brood size and female survival during the breeding period were examined in a large-scale experiment, involving 3591 mature noble crayfish, Astacus astacus L., females. Crayfish density during both mating/spawning and winter incubation had major effects on egg survival. In the high density experiment (67 and 44 individuals per m² during mating/spawning and winter incubation respectively) mean pleopod egg number in April was 18-20. Lowering the density to 50 during mating/spawning (still 44 individuals per m² during winter incubation) gave mean pleopod egg numbers of 31-38. In the low density experiment (50 and 33 individuals per m² during mating/spawning and winter incubation) mean pleopod egg numbers were 44-46. Egg-bearing females held in individual compartments with perforated bottom had a mean pleopod egg number of 25. Female survival during winter incubation was high, ranging from 91.8 to 98.3%. Covering the basins had no distinct effect on egg and female survival. In Astacus astacus culture we recommend that crayfish density should not exceed about 50 individuals per m² during mating/spawning and about 33 individuals per m² during winter incubation.     

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.     

Hormone Induced Spawning of Summer Flounder Paralichthys dentatus

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

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.     

Out-of-season spawning of pike perch (Sander lucioperca L.) without the need for hormonal treatments

The provision of fry and fingerlings, independent of the natural spawning season, can facilitate the implementation of innovative rearing strategies also in pike perch ( Sander lucioperca L.). As strict pharmaceutical acts or codes of conduct for organic aquaculture can constrain fish farmers in inducing spawning with hormonal applications, this study intended to develop protocols for advanced and postponed spawning just by simple photo-thermal treatments. After spending between 31 and 61 days at temperatures below 10 °C, different groups of pike perch spawners were treated with light and temperature programmes to advance spawning. Reproduction could be induced successfully 2 months before the natural spawning season when the mating pairs spent 43 or more days below 10 °C, followed by a maturation phase of 44–68 days at 15 °C and 16 h illumination per day. Advanced spawning could be documented for 32 out of 35 females (91%) that underwent photo-thermal treatments. Mean commercial fecundities up to 24% and average rates of developing eggs of 65% were observed in advanced spawning groups. Coldbanking of mature females allowed to postpone spawnings for 2 and 3 months. However, no egg development could be recorded in these treatment groups.     

Reproduction of Penaeus kerathurus using eyestalk ablation

In a preliminary experiment on the induction of sexual maturity in Penaeus kerathurus by unilateral eyestalk ablation, spawning was obtained in 94% of the females treated. The time necessary to reach the spawning stage appeared to be closely related to the stage of natural physiological development of the gonads and the length of the photoperiod, the period between ablation and spawning decreasing from 69 days for females treated in November to about 10 days for females treated at the beginning of their natural reproductive period in May/June. Spawning after treatment was repeated up to eight times, sometimes at intervals of less than 10 days, without showing a decrease in the amount of fertile spawn. The mean number of fertile eggs per spawn was 78.400, which is not significantly different from the corresponding mean obtained previously after thermal stimulation of almost mature breeders; the hatching percentage, 67%, was also similar. Often only the anterior and median lobes of the ovaries are included in the spawning process. The discharged spawn is nearly always completely free of matrix material. It is anticipated that induction by eyestalk ablation could allow a considerable extension of the growing season and of the area suitable for 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.     

Characterization and comparison of variations in reproductive performance of Chitralada strain Nile tilapia, Oreochromis niloticus (L.)

In an attempt to better understand and characterize the variability in the female reproduction of individual Thai‐Chitralada strains of Nile tilapia, Oreochromis niloticus (L.), tagged mature females (n=68) from a single population were monitored in a hapa‐in‐pond system over a 12‐month experimental period. Spawn female⁻¹, eggs female⁻¹ day⁻¹, eggs kg female⁻¹ day⁻¹, day spawn⁻¹ and weight (g) at first spawning of individual females were determined from the regular weekly sampling of weight (g) and eggs per spawn. For analysis, the females were grouped into two, high spawning (HSF) and low spawning frequency (LSF) classes based on their spawning frequency (SF) record. Moreover, nested under these two classes were two groups each based on growth rate, i.e., high frequency – large size (HL), high frequency – small size (HS), low frequency – large size (LL) and low frequency – small size (LS). There was no difference in eggs spawn⁻¹ among all females. The HSF group produced 68% and 361% more eggs female⁻¹ day⁻¹ than the population mean and LSF group respectively. Eggs female⁻¹ day⁻¹ and spawn female⁻¹ remained high in the HSF group and low in the LSF group throughout the 12‐month experimental period. This suggests that individual female spawning activity is consistent within a population in a common environment. The inter‐spawn interval increased with age in all four groups, and day spawn⁻¹ was shorter by 130% in HSF females compared with day spawn⁻¹ in LSF. The HSF group also spawned more successively (≥3), while the LSF group of females had fewer successive spawns (≤2). Body weight (g) had no influence on the number of eggs produced. The study indicates that separating frequently spawning females could be used as an important strategy to improve commercial seed production of Nile tilapia.     

异齿裂腹鱼人工规模化繁殖技术研究

2010年4～6月,对野生异齿裂腹鱼(Schizothorax o' connori)人工规模化繁殖技术进行研究,并初步进行产后亲鱼恢复培养技术研究.对108尾雌鱼进行干法人工授精,共采卵104万多粒,孵出仔鱼62万多尾.其中45尾雌亲鱼自然成熟,共采卵46.8万多粒,平均受精率和孵化率低于人工催产雌鱼卵.人工催产83...     

Induced Spawning and Egg Quality Evaluation of Red Snapper, Lutjanus campechanus

Brood red snapper, Lutjanus campechanus, were captured from the wild and induced to ovulate by human chorionic gonadotropin (hCG) injection; eggs and sperm were manually stripped; and the eggs were artificially fertilized. Eggs were evaluated by the following egg quality parameters: buoyancy, fertilization, egg size, and oil globule size and number. The relationship of these egg quality parameters and brood characteristics (female size, fecundity, time of year, and response time to ovulation) to 36 h posthatch larval survival was considered. Injection of wild‐caught red snapper females with 1100 IU/kg of hCG resulted in 75% of the females ovulating. The average fecundity was 343,377 ± 30,805 eggs/kg, with a mean percent fertilization of 79.0 ± 1.74%. The mean percentage of floating eggs per spawn was 91.8 ± 1.75%. Mean egg diameter for floating eggs was 778.3 ± 2.09 μm, with a mean oil globule diameter of 117.5 ± 1.53 μm. Brood‐related characteristics were a better predictor of larval survival than postovulation egg characteristics. The percentage of floating eggs in a spawn was not correlated to larval survival. Spawns with eggs having a single oil globule had a similar larval survival as those eggs where multiple globules were common. No clear relationships were found for any one factor and larval survival, but rather a combination of factors was more predictive of survival, most notably spawn date, fecundity, and response time following hCG injection.     

Artificial spawning of carp (Cyprinus carpio L.): differences between females of Polish strain 6 and Hungarian strain W treated with carp pituitary homogenate, Ovopel or Dagin

Investigations of the effects of controlled reproduction were conducted on carp females of Polish strain 6 and Hungarian strain W after ovulation stimulation with carp pituitary homogenate (CPH) (0.3 mg+2.7 mg kg^?1 body weight), Ovopel (1/5+1 pellet kg^?1 body weight) or Dagin (1 dose kg^?1 body weight). In both strains, the highest percentage of spawning females was found after the Ovopel treatment. After treatments with CPH and Dagin this percentage did not differ in strain 6; however, after Dagin, it was higher in fish of strain W. After CPH or Ovopel stimulation the females of line 6 yielded eggs of higher weight compared with line W. After the Dagin treatment the weight of eggs obtained from females, both strains was similar but much lower than after the two remaining agents. The quality of eggs expressed both by the percentage of fertilization and that of living embryos after 24 and 36 h incubation was similar in the two strains only in the group treated with Ovopel. After CPH application eggs of better quality were obtained from strain 6 compared with strain W; however, after the treatment with Ovopel, eggs of much better quality were noted in strain W. In general, the best effects of reproduction were recorded in the case of Ovopel and the poorest in that of Dagin. Females of strain 6 yielded eggs of a higher weight but the percentages of spawning females were higher in strain W after each of the applied spawning agents. A new approach to this problem consisted in investigating the interaction between ovulation stimulators and origin of females of fish treated with Dagin.