Induced spawning in perch, Perca fluviatilis L. using carp pituitary extract and HCG

Induced spawning in Eurasian perch, Perca fluviatilis L., was studied using human chorionic gonadotrophs (hCG) or acetone-dried common carp pituitary with or without hCG. The dose administered to fish was 5700 IU hCG kg^-1 or 4.0 mg kg^-1 carp pituitary with or without 500-700 IU hCG kg^-1 for females and 2850 IU hCG kg^-1 or 2.0 mg kg^-1 carp pituitary with or without 250-350 IU hCG kg^-1 for males. There were no statistically significant differences in quantity of milt in treated and control groups, although the best result was observed when males were treated with a triple injection of hCG and carp pituitary extract. Male spermiating success, expressed as a quantity of milt, was negatively correlated with fish weight. All females treated in this experiment had oocytes at the same division, so time of ovulation was highly synchronous. Spawning success, expressed as a spawning effectivity coefficient (S_c), was highest in fish treated with the triple injection. Spawning methods described in this paper were successful, even though hormones from another order of fish were used.     

Induction of Out-of-Season Spawning of Pikeperch, Sander Lucioperca (L.)

Pikeperch were induced to spawn 3 months prior to the natural spawning period through photothermal and hormonal stimulation. Females (five specimens in each group) were stimulated with injection of human chorionic gonadotropin (hCG) once (200 IU kg^–1), twice (200 IU kg^–1, second dose after 48 h–400 IU kg^–1) or three times (200 IU kg^–1, after 24 h–200 IU kg^–1 and after another 24 h–200 IU kg^–1). The control group was injected once with 0.9% NaCl. The males were stimulated with a single hormone dose of 200 IU kg^–1. Eggs were obtained from all the hormonally treated fish. None of the control group females, which were only stimulated photothermally, ovulated any eggs. The time of ovulation was 66–71 h following the first injection, and the eggs viability until the eyed stage (from 71.5 to 77.5%) did not depend on the number of hormone doses (P > 0.05). The out-of-season spawning method described in this paper could be used to provide pikeperch larvae for intensive culture systems (recirculating water systems) before natural spawning season and to produce larger-sized pikeperch fingerlings for stocking.     

Increase in milt production by hormonal treatment in the pejerrey fish Odontesthes bonariensis (Valenciennes 1835)

In spite of interest in the cultivation of the pejerrey fish Odontesthes bonariensis (Cuvier & Valenciennes 1835), there are few studies on subjects required to advance this activity. One of the problems is the synchronization of female and male maturation to provide eggs and sperm for larval production. The low volume of expressible milt, either in wild or culture fish, is a major problem. The aim of this work was to study the effectiveness of the administration of different hormones on sperm production in pejerrey. Milt production was enhanced by the injection of human chorionic gonadotropin (hCG) (16.7‐fold increase, 625 IU kg^?1), carp pituitary extracts (13.5‐fold increase, 30 mg kg^?1), salmon pituitary extracts (12.8‐fold increase, 30 mg kg^?1), salmon‐type gonadotropin‐releasing hormone analogue (GnRH) (16.7‐fold increase, 10 μg kg^?1) and mammalian‐type GnRH analogue (10.8‐fold increase, 20 μg kg^?1). Sperm concentration, motility and the fertilization rate were not statistically different compared with control groups. It was also demonstrated that sperm could be obtained off‐season. Taken together, hCG is recommended to stimulate pejerrey spermiation because it is effective in low doses is inexpensive and is widely available.     

Artificial spawning of carp (Cyprinus carpio L.); differences between the effects of reproduction in females of Hungarian, Polish and French origin treated with carp pituitary homogenate or [D-Tle6, ProNHEt9] GnRH (Lecirelin)

The investigation concerned the reproduction effects in carp females of the Hungarian strain 8, Polish strain 2 and French strain F of ovulation stimulation with carp pituitary homogenate (0.3 mg kg^?1 and after 12 h 2.7 mg kg^?1) or [D‐Tle⁶, ProNHEt⁹]GnRH (Lecirelin) with metoclopramide (15 μg kg^?1 and 10 mg kg^?1 respectively). The ovulation stimulators did not affect the weight of eggs (expressed in g and as the percentage of female body weight). However, in the group treated with pituitary homogenate (I) the least‐square means estimated for these parameters were higher than in the group treated with Lecirelin (II). A statistically significant (P≤0.05) difference in the mean percentage of living embryos after 48‐h incubation was observed between groups I and II, with the eggs obtained from females of group I being of better quality. The origin of females significantly (P≤0.05) affected the weight of eggs. The weight of eggs from females of Hungarian strain 8 was higher (P≤0.05) than the weight of eggs of the other two lines. With respect to parameters for egg quality (percentage of fertilized eggs and percentage of living embryos after 24‐, 36‐ and 48‐h incubation), no effect of the origin of females was observed. The interaction between the spawning agent and the origin of the females was not statistically significant with respect to the two parameters for the weight of the eggs. The least‐square means test for the investigated interaction showed that after the application of pituitary homogenate, the weight of eggs obtained from strains 8 and F was similar (respectively 711.2 g and 665.0 g). However, after the application of Lecirelin the females of strain 8 yielded eggs of a high weight (934.3 g) and those of strain F of a very low weight (373.2 g). A statistically significant (P≤0.05) interaction between ovulation stimulator and origin of females was recorded for the percentage of living embryos after 24‐ and 36‐h incubation. A dependence was found between the latency time and the reproduction effects.     

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.     

Reproductive performance in induced and spontaneous spawning of the mangrove red snapper, Lutjanus argentimaculatus: a potential candidate species for sustainable aquaculture

A reliable breeding technique was developed for the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775), to help sustain the aquaculture of this immensely popular species in Southeast Asia. Using standardized indices of female maturity (based on mean oocyte diameter of ≥0.40 mm), time of injection (1000–1130) and sex ratio (one female to two males), a single injection of 100 μg kg^?1 luteinizing hormone‐releasing hormone analogue (LHRHa) (n=16 fish), but not 50 μg kg^?1 (n=five fish), successfully induced egg (62.5% success rate) and larval (43.8%) production. Human chorionic gonadotropin (hCG) at 500 IU kg^?1 (n=five fish) also failed to induce spawning, but doses of 1000 (n=22 fish) and 1500 IU kg^?1 (n=15 fish) gave spawning (77.3% and 80.0% respectively) and hatching success rates (72.7% and 60.0% respectively) that were not significantly different from those of 100 μg kg^?1 LHRHa. No spawning was observed in saline‐injected controls (n=seven fish). While mean spawning latency, egg diameter, egg production per spawn, percent egg viability, hatching rate, percent of normal larvae and cumulative survival of eggs to normal larvae did not differ significantly among the effective hormones and doses, 1000 IU kg^?1 hCG had a higher percentage (76.5%) of total spawns with egg production per spawn in excess of one million than those of 1500 IU kg^?1 hCG (50.0%) and 100 μg kg^?1 LHRHa (40.0%). Mangrove red snapper spontaneously spawned from March–April to November–December with a peak of egg collection and spawning in May–June. Egg collection per spawn ranged from 0.05 to 6.35 million. Spontaneous spawning of mangrove red snapper exhibited lunar periodicity with spawns mostly occurring 3 days before or after the last quarter and new moon phases and occurred consistently between 02:00 and 04:00 hours. High fecundity and good egg quality, coupled with the ability to respond to induce spawning or natural spawning in captivity, provide a sound basis for improving the sustainability of red snapper aquaculture in Southeast Asia.     

Induced spawning in perch, Perca fluviatilis L., using FSH + LH with pimozide or metoclopramide

Induced spawning in perch, Perca fluviatilis L., was studied using follicle stimulating hormone and lutenizing hormone (FSH + LH) with the addition of pimozide or metoclopramide. The doses administered to fish were: 75 IU kg^?1 of FSH + LH with 5 or 10mgkg^?1 of pimozide (P) or metoclopramide (M) in females, and 25 IU kg^?1 of FSH + LH with 2.5 or 5 mg kg^?1 of P or M in males. Hormonal injections in males (except the injection of FSH + LH with 10 mg kg^?1 of M) did not influence the quantity of milt obtained. All females treated in this experiment had oocytes at the same stage of nucleus migration, so the time of ovulation was very synchronous, i.e. 16-24 h after injection. The relationship between the quality of the eggs, expressed as a survival to eyed-egg stage, and latency was inverse. Spawning success, expressed as a spawning effectiveness coefficient (S_e), was highest in the fish that had been treated with FSH + LH with a higher dose of M.     

Artificial spawning of carp Cyprinus carpio L.: differences between the effects on reproduction in females of Polish and Hungarian provenance treated with carp pituitary and (D-Ala6) GnRH ProNHEt (Kobarelin)

Ovulation was stimulated in carp females of Polish and Hungarian provenance using injections of ( d ‐Ala⁶) GnRH ProNHEt (Kobarelin) (20 μg kg^?1) with metoclopramide (10 mg kg^?1) or carp pituitary (3 mg kg^?1). For estimating the effects of the substance stimulating ovulation and of the female provenance, analysis of variance was carried out using the least squares method. It was found that the stimulating substance, provenance and interaction of these factors did not significantly affect the weight of eggs obtained. On the other hand, the stimulating substance, provenance and interaction had a highly significant (P ⩽ 0.0001) effect on the percentages of fertilization and live embryos. Females of Hungarian provenance treated with Kobarelin yielded eggs of much better quality but a smaller weight than after the pituitary treatment. In the case of carp females of Polish provenance, a yield of eggs of smaller weight and very poor quality was noted compared with the weight and quality of eggs obtained after hypophysation.     

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.     

Artificial spawning of female Lithuanian strain B carp (Cyprinus carpio L.) after treatment with carp pituitary homogenate, Ovopel or [d-Tle6, ProNHEt9] GnRH-a (Lecirelin)

The results of reproduction of females from Lithuanian strain B carp after ovulation stimulation with carp pituitary homogenate (CPH; 0.3+2.7 mg kg^?1; group I), Ovopel (1/5+1 pellet kg^?1; group II) or [d ‐Tle⁶, ProNHEt⁹] GnRH‐a (Lecirelin) with metoclopramide (15 μg kg^?1+10 mg kg^?1 respectively; group III) were investigated. The lowest percentage of spawning females (71%) was recorded in the group treated with CPH. In case of Ovopel or Lecirelin induced ovulation, 86% of females spawned. No statistically significant effect of the ovulation stimulator (group) on the weight of eggs was found; however, the highest mean weight of eggs (expressed both in grams and in the percentage of female body weight) was recorded for the group treated with Ovopel (1400 g and 13%). After the treatment with CPH or Lecirelin, the weight of eggs was 1140 g (11%) and 1100 g (10%) respectively. The ovulation stimulator significantly affected the percentage of live embryos after 36 and 48 h incubation of eggs (P≤0.05; P≤0.01). After treatment with [d ‐Tle⁶, ProNHEt⁹] GnRH‐a, eggs of the best quality were obtained and after 36 and 48 h incubation the mean percentages of live embryos were significantly higher than the means calculated for the remaining two groups. No statistically significant differences were found between the percentage of living embryos after 36 and 48 h incubation of groups I and II.     

Artificial spawning of carp (Cyprinus carpio L.): the use of Aquaspawn and carp pituitary to induce ovulation in females of Lithuanian line B

Ovulation stimulation was carried out in carp (Cyprinus carpio L.) females of Lithuanian line B, using carp pituitary (0.3 + 2.7 mg kg^?1), Aquaspawn (0.5 mL kg^?1) and Aquaspawn + carp pituitary (0.3 mL kg^?1 + 2.7 mg kg^?1). The poorest results of reproduction (the lowest percentage of ovulating females, the lowest weight of eggs and their poorest quality) were obtained after double hypophysation. The best results were induced by the application of Aquaspawn alone. The effect of the applied stimulators was statistically non‐significant with respect to the weight of eggs, being highly significant (P ≤ 0.01) with respect to the percentage of fertilized eggs and that of living embryos after 24‐ and 36‐h incubation. The multiple‐regression equations were calculated for the three groups separately. The percentage of living embryos after 36‐h incubation constituted a dependent variable while the mass of females, the mass of eggs, the fertilization percentage and the percentage of living embryos after 24‐h incubation were independent variables. The regression was only significant (P ≤ 0.01) for the group of fish treated with Aquaspawn.     

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.     

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%).     

Augmentation of free amino acids in eggs of red snapper,Lutjanus campechanus as part of the induced spawning protocol

An attempt was made to increase free amino acids (FAA) concentrations in eggs of red snapper Lutjanus campechanus as part of an induced spawning protocol. Mature female red snapper were given intramuscular injections of human chorionic gonadotropin (HCG) at a 1100 IU kg^?1 of female body weight. Immediately after the HCG injection, one set of females received an intramuscular injection of FAA in a buffered saline solution at a dose of 20 mg FAA cocktail kg^?1 of body weight. The FAA cocktail was 25% isoleucine, 25% leucine, 25% lysine and 25% valine on a molecular weight basis. A second set of fish did not receive the FAA supplement. Both sets of fish were equally successful in spawning with ovulation occurring 21–32.5 h post injection. Injection of FAA into brooders as eggs began final maturation and hydration resulted in an increase in leucine (nmoles mg egg^?1) and a slight increase in isoleucine (nmoles egg^?1) in recently ovulated eggs. FAA supplementation via brood injection altered FAA utilization rates by embryos and during larval development, resulted in a greater yolk sac and oil globule reserve in larvae as they approached the time of first feeding.     

Hormonal induction of ovulation in pikeperch (Sander lucioperca L.) using human chorionic gonadotropin (hCG) and mammalian GnRH analogue

The aim of the present study was to study spawning stimulation in artificial reproduction of females pikeperch (Sander lucioperca L.) using “Chorulon” containing the human chorionic gonadotropin (hCG) and compare with “Supergestran” containing a mammalian GnRH ([D-Ala⁶]GnRHProNhet) analogue. The females were divided into eleven experimental groups and injected with hCG at 250, 500, 750, and 1 000 IU kg^?1 body weight (BW) and mGnRHa at 1, 2.5, 5, 10, 25, and 50 μg kg^?1 BW. In all treatments, a single intramuscular injection of hormone was performed. Control group was injected with 0.9 % NaCl, 0.9 cm³ kg^?1 BW. The average percentages of ovulating females were 88.5 ± 12.3 and 80.8 ± 10.9 % in hCG- and mGnRHa-treated groups, respectively. The average diameter of eggs was 0.95 ± 0.06 and 0.98 ± 0.06 mm in hCG- and mGnRHa-treated groups, respectively. Neither ovulation rate nor diameter of egg was statistically differed among hormonally treated groups. Statistical difference was observed only in hatching rate, where the average were 73.6 ± 14.4 and 50.6 ± 17.7 % in hCG and mGnRHa-treated groups, respectively. Among hormonally treated groups, the best results were observed in groups treated with hCG at 500 and 750 IU kg^?1 and in groups treated with mGnRHa at 25 μg kg^?1. No ovulation was observed in the control group. This study indicated successful ovulation in pikeperch using a single intramuscular injection of hCG or mGnRHa analogue.     

Artificial spawning of European catfish, Silurus glanis L.: stimulation of ovulation using LHRH-a,Ovaprim and carp pituitary extract

Ovulation was stimulated in four groups of European catfish, Silurus glanis L., using injections of des-Gly¹⁰, [D-Ala⁶]-LHRH Ethylamide (20 μg kg^–1) and pimozide (10 mg kg^–1), Ovaprim (0.33 mL kg^–1), and carp pituitary extract (4 mg kg^–1, in one or two doses). A higher percentage of ovulating females (producing eggs of sufficient quality) was found after the LHRH-a and Ovaprim treatments (100% and 80%) in relation to fish treated with the pituitary extract (60% and 66.67%). The greatest weight of eggs was obtained in the case of repeated hypophysation and LHRH-a (1299.69 and 1298.57 g, respectively), and the smallest after single hypophysation (1144.08 g). After 60 h of incubation, the best quality of eggs was found in the group treated with Ovaprim (62.9% of live embryos) and the poorest in the two groups which underwent hypophysation (50.41% and 50.75%). No statistically significant effect by the ovulation stimulators on the characteristic qualitative and quantitative traits of obtained eggs was ascertained.     

Evaluation of various hCG treatment strategies applied to domesticated pikeperch (Sander lucioperca) broodstock on nest-spawning performance

The aim of the present study was to evaluate the effects of hCG injections on reproductive efficiency by hCG treatment in both male or female brooders of domesticated pikeperch (Sander lucioperca) in the first generation. The study consisted of four treatments based on hormone injection to male or female brooders including T1: both sexes were injected, T2: only females were injected, T3: only males were injected, and T4: without hormone injection. Each treatment which included 14 males and 12 females were introduced to a single rectangular concrete tank with one spawning nest for each mate (a total of 12 nests per tank). Fish were injected by a single dose of 200 IU/kg hCG before transferring to mating tanks. After mating, nests containing fertilized eggs were transferred to circular concrete tanks for incubation and hatching of embryos. According to the results, treatments T3 and T4 did not respond to hormonal stimulation and no fish were spawned. Treatments T1 and T2 showed a positive response to hormone injection. Latency time, fertilization rate, and hatching rate showed no significant difference between T1 and T2 (P?>?0.05), but the number of responded females was significantly higher in T2 (P?<?0.05). The results of the present study demonstrated that it is possible to perform the semi-artificial propagation of domesticated pikeperch via injecting with 200 IU/kg hCG just to females, without the need for hormonal stimulation for males.

     

The kinetic profile of oxolinic acid in sharpsnout sea bream, Diplodus puntazzo (Cetti 1777)

The pharmacokinetics of oxolinic acid (OA) were investigated after a single intra‐vascular injection (20 mg kg^?1 fish) in sharpsnout sea bream (90 g), a promising new euryhaline species for Mediterranean fish farming. The distribution half‐life (t_1/2α) and the elimination half‐life (t_1/2β) of OA were calculated to be 0.4 and 10 h respectively. The apparent volume of distribution at steady‐state (V_d(ss)) and total clearance rate (CL_T) of the drug were found to be 2.1 L kg and 0.2 L kg^?1 h^?1 respectively. The bioavailability (F%) of OA following oral administration (40 mg kg^?1 fish) was estimated to be 15%. The results indicate a rapid distribution and elimination of the drug, moderate tissue penetration, but low absorption in sharpsnout sea bream. The kinetic profile of OA found in this species is comparable with that observed in another well‐known sparid, gilthead sea bream.     

Out-of-season spawning of cultured pikeperch [Sander lucioperca (L.)]

The aim of this study was to determine the effectiveness of out‐of‐season spawning of cultivated pikeperch (fish that were reared from the larval stage in re‐circulating systems and fed commercial feed exclusively) stimulated hormonally with human chorionic gonadotropin (hCG). The impact of fish age (2+ and 3+) and hormone dosage [200 or 400 IU hCG kg⁻¹ body weight (BW)] on spawning was analysed and expressed as the share of stripped females, commercial fecundity (% BW) and survival of embryos until the eyed‐egg stage (EES index). The possibility of utilizing changes in female pikeperch body weight (CBW index) that are observed following hormone injections as an additional indicator for determining maturity was also investigated. The age and hormone dosage were not noted to have a significant impact on the number of stripped females (≥80% on all groups), the latency period (90–100 h), commercial fecundity (11.3–13.3% BW) or the values of the EES index (61–73%; P>0.05). The mean value of EES from the 3+ age group females was higher than that in the 2+ females, and the interaction between the tested factors (fish age and hormone dosage) wasstatistically significant (P<0.05). In the fish from the control group (injected with a 0.9% NaCl solution), no progress was noted in the maturation of oocytes and no eggs were obtained from any female. It was noted that these females lost BW over the course of the subsequent 24 h of the measurements (P<0.05). In the groups of females that were stimulated hormonally, the opposite phenomenon was observed; in these groups, the CBW index increased significantly between 48 and 96 h following hormone injection. The value of the CBW index was not noted to have been statistically significantly determined by either hormone dose or fish age (P>0.05). The regression equations that described the dependence between CBW and the oocyte maturity stage were highly significant statistically, and the determination coefficient R² assumed a value of 0.76. The most significant increase in BW was related to the oocytes achieving maturity stage III. The BW of pikeperch females with oocytes in this stage was 103% higher than the initial BW. This might be a valuable and useful tool for determining maturity in females of this fish species.     

Spawning season,spawning grounds,and egg production of red sea bream in Hiuchi-nada,Seto Inland Sea

The spawning season and grounds of red sea bream in Hiuchi-nada, the central part of the Seto Inland Sea, were described using a new method based on monoclonal antibodies for identifying Pagrus major eggs, and the daily egg production (standardized by the incubation time and survival rate) was estimated. At the peak of spawning (May), the ranges of sea temperature, salinity, and chlorophyll a where red sea bream eggs occurred were 14.8–17.4°C, 32.0–33.0, 0.5–4.4 μg/L, respectively. The main spawning grounds of the red sea bream were confirmed as being the areas near the Geiyo Islands, Misaki Peninsula, Saijyo, Niihama. The spatial spread of red sea bream eggs increased with the egg developmental stage. The ranges of daily egg production in 2005 and 2006 were 0.3–19.3 and 0.2–6.7 × 10⁹ eggs/day, respectively. In Hiuchi-nada, aquaculture farms are located close to the spawning grounds, and the potential spawning population from the aquaculture farms equaled or exceeded that of the estimated spawning population obtained by the egg production method. Red sea bream eggs in Hiuchi-nada might be produced by both wild and aquaculture-based spawning populations.