ABSTRACT Artificial reproduction in eels is very challenging due to their peculiar life cycle. No... more ABSTRACT Artificial reproduction in eels is very challenging due to their peculiar life cycle. No information is yet available on the influence of photoperiod on the sexual development of wild silver eels in captivity. Previous studies have demonstrated the photoperiod to influence sexual maturation of eels showing that dark conditions lead to a better reproductive performance in terms of a greater gonadal maturation and a higher egg production and spawning record. This study aimed to investigate the physiological mechanisms leading to different outcomes in light or dark conditions on the gonadal steroidogenesis in wild female European silver eels during pituitary extract treatment. The variation of the body weight index and gonadosomatic index suggested a positive effect in dark conditions. Sexual steroids (androgens and estrogens) showed a significant difference in plasmatic concentration in the animals kept in the dark suggesting a better wellness reproductive situation in this particular housing condition.
ABSTRACT A review of the studies carried out from 2010 to 2013 on the reproduction of the Europea... more ABSTRACT A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: effects of photoperiod, evaluation of different populations, a new recirculating system, first successful weaning test.
Artificial reproduction in eels is very challenging due to their peculiar life cycle. No informat... more Artificial reproduction in eels is very challenging due to their peculiar life cycle. No information is yet available on the influence of photoperiod on the sexual development of wild silver eels in captivity. Previous studies have demonstrated the photoperiod to influence sexual maturation of eels showing that dark conditions lead to a better reproductive performance in terms of a greater gonadal maturation and a higher egg production and spawning record. This study aimed to investigate the physiological mechanisms leading to different outcomes in light or dark conditions on the gonadal steroidogenesis in wild female European silver eels during pituitary extract treatment. The variation of the body weight index and gonadosomatic index suggested a positive effect in dark conditions. Sexual steroids (androgens and estrogens) showed a significant difference in plasmatic concentration in the animals kept in the dark suggesting a better wellness reproductive situation in this particular...
A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: ef... more A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: effects of photoperiod, evaluation of different populations, a new recirculating system, first successful weaning test.
ABSTRACT This study aimed to compare the fertility of eggs between artificially matured female si... more ABSTRACT This study aimed to compare the fertility of eggs between artificially matured female silver eels that spawned spontaneously and those that were spawned by manual stripping. The effects of the two methods of spawning on ovulation and fertilization rate were also investigated. For this purpose, 18 wild female European eels captured in Bonello lagoon (North Adriatic Sea) were carp pituitary extract-injected to undergo sexual maturation and ovulation; a final injection of 17,20β-dihydroxy-4-pregnen-3-one (DHP) was administered when at least 30% of the oocytes were fully transparent. After the DHP-injection, nine eels were transferred to a new closed recirculating aquaculture system, where they were housed with spermiating males (sex ratio 4/1) to allow spontaneous spawning (SPT-group); the remaining nine eels were transferred to a 250 L tank and ovulation was checked at four-hourly intervals by manual stripping (STR-group). The number of eggs per female in the SPT-group was significantly greater than that in the STR-group. Furthermore, fertilization rates in the SPT-group were notably higher than those observed in the STR-group. Significantly, the best performances were obtained among eels in which at least 50% of oocytes were fully transparent at the time DHP was administered. We conclude that the fertility of eggs from spontaneously spawning eels is superior to that of eggs acquired by strip-spawning and artificial fertilization.
The aim of this work was to determine the effects of dark and light conditions on the E2, testost... more The aim of this work was to determine the effects of dark and light conditions on the E2, testosterone and thyroid hormones levels and on the gene expression levels (vitellogenin 1, vitellogenin 2, and estradiol receptor one) in European eels (Anguilla anguilla) during ovarian development induced by increasing doses of carp pituitary extracts (CPEs). The subjects were divided into 2 groups: 14-hour light:10-hour dark (Light Group) and 24-hour darkness (Dark Group). All the eels received intramuscular injections with CPE at a dosage of 10 mg/kg body weight (BW) once a week for the first 3 weeks, 20 mg/kg BW fourthsixth week, 30 mg/kg BW seventh-ninth week, and 40 mg/kg up to the end of the experiment (13th week). Vitellogenin and estradiol receptor expression levels did not show significant differences between the two housing conditions whereas in both groups vitellogenin mRNA increased starting from first CPE injection. Testosterone and 17-beta estradiol plasma levels were significantly greater in the Dark Group compared with the Light Group starting from the ninth and the 13th week, respectively. These results suggest that darkness could be a useful variable for standardizing gonadal maturation in eels kept in captivity.
Pituitary homogenate 11-Ketotestosterone dramatically affects ovarian physiology in previtellogen... more Pituitary homogenate 11-Ketotestosterone dramatically affects ovarian physiology in previtellogenic eels, notably increasing lipid accumulation and the expression of the follicle-stimulating hormone receptor. We therefore sought to combine androgen pre-treatment of female silver eels with "traditional" hypophysation in order to assess whether androgens constitute a valuable addition to induced spawning protocols. Eels were first implanted with different doses (0-30 mg) of 17-methyltestosterone to evaluate effects on oocyte size. Females (Trial I) were subsequently subjected to repeated injections with carp pituitary homogenate to artificially induce maturation. In a subsequent trial, we used 1 mg of androgen, implanted in either aromatizable (androstenedione) or non-aromatizable form (11-ketotestosterone) and again induced eels to mature artificially by repeated injections with carp pituitary homogenate. Androgen treatment significantly increased oocyte diameters prior to commencing carp pituitary homogenate treatment. Thereafter, less time, less money and less handling were required to reach the pre-ovulatory stage, while retaining comparable amounts of lipid in ovulated eggs. We contend that androgen pre-treatment has promise as a synchronizing and cost-effective measure for the artificial induction of maturation in anguillid eels.
European eels live most of their lives in freshwater until spawning migration to the Sargasso Sea... more European eels live most of their lives in freshwater until spawning migration to the Sargasso Sea. During seawater adaptation, eels modify their physiology, and their digestive system adapts to the new environment, drinking salt water to compensate for the continuous water loss. In that period, eels stop feeding until spawning. Thus, the eel represents a unique model to understand the adaptive changes of the enteric nervous system (ENS) to modified salinity and starvation. To this purpose, we assessed and compared the enteric neuronal density in the cranial portion of the intestine of freshwater eels (control), lagoon eels captured in brackish water before their migration to the Sargasso Sea (T0), and starved seawater eels hormonally induced to sexual maturity (T18; 18 weeks of starvation and treatment with standardized carp pituitary extract). Furthermore, we analyzed the modification of intestinal neuronal density of hormonally untreated eels during prolonged starvation (10 weeks) in seawater and freshwater. The density of myenteric (MP) and submucosal plexus (SMP) HuC/D-immunoreactive (Hu-IR) neurons was assessed in wholemount preparations and cryosections. The number of MP and SMP HuC/D-IR neurons progressively increased from the freshwater to the salty water habitat (control > T0 > T18; P < 0.05). Compared with freshwater eels, the number of MP and SMP HuC/D-IR neurons significantly increased (P < 0.05) in the intestine of starved untreated salt water eels. In conclusion, high salinity evokes enteric neuroplasticity as indicated by the increasing number of HuC/D-IR MP and SMP neurons, a mechanism likely contributing to maintaining the body homeostasis of this fish in extreme conditions.
ABSTRACT Artificial reproduction in eels is very challenging due to their peculiar life cycle. No... more ABSTRACT Artificial reproduction in eels is very challenging due to their peculiar life cycle. No information is yet available on the influence of photoperiod on the sexual development of wild silver eels in captivity. Previous studies have demonstrated the photoperiod to influence sexual maturation of eels showing that dark conditions lead to a better reproductive performance in terms of a greater gonadal maturation and a higher egg production and spawning record. This study aimed to investigate the physiological mechanisms leading to different outcomes in light or dark conditions on the gonadal steroidogenesis in wild female European silver eels during pituitary extract treatment. The variation of the body weight index and gonadosomatic index suggested a positive effect in dark conditions. Sexual steroids (androgens and estrogens) showed a significant difference in plasmatic concentration in the animals kept in the dark suggesting a better wellness reproductive situation in this particular housing condition.
ABSTRACT A review of the studies carried out from 2010 to 2013 on the reproduction of the Europea... more ABSTRACT A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: effects of photoperiod, evaluation of different populations, a new recirculating system, first successful weaning test.
Artificial reproduction in eels is very challenging due to their peculiar life cycle. No informat... more Artificial reproduction in eels is very challenging due to their peculiar life cycle. No information is yet available on the influence of photoperiod on the sexual development of wild silver eels in captivity. Previous studies have demonstrated the photoperiod to influence sexual maturation of eels showing that dark conditions lead to a better reproductive performance in terms of a greater gonadal maturation and a higher egg production and spawning record. This study aimed to investigate the physiological mechanisms leading to different outcomes in light or dark conditions on the gonadal steroidogenesis in wild female European silver eels during pituitary extract treatment. The variation of the body weight index and gonadosomatic index suggested a positive effect in dark conditions. Sexual steroids (androgens and estrogens) showed a significant difference in plasmatic concentration in the animals kept in the dark suggesting a better wellness reproductive situation in this particular...
A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: ef... more A review of the studies carried out from 2010 to 2013 on the reproduction of the European eel: effects of photoperiod, evaluation of different populations, a new recirculating system, first successful weaning test.
ABSTRACT This study aimed to compare the fertility of eggs between artificially matured female si... more ABSTRACT This study aimed to compare the fertility of eggs between artificially matured female silver eels that spawned spontaneously and those that were spawned by manual stripping. The effects of the two methods of spawning on ovulation and fertilization rate were also investigated. For this purpose, 18 wild female European eels captured in Bonello lagoon (North Adriatic Sea) were carp pituitary extract-injected to undergo sexual maturation and ovulation; a final injection of 17,20β-dihydroxy-4-pregnen-3-one (DHP) was administered when at least 30% of the oocytes were fully transparent. After the DHP-injection, nine eels were transferred to a new closed recirculating aquaculture system, where they were housed with spermiating males (sex ratio 4/1) to allow spontaneous spawning (SPT-group); the remaining nine eels were transferred to a 250 L tank and ovulation was checked at four-hourly intervals by manual stripping (STR-group). The number of eggs per female in the SPT-group was significantly greater than that in the STR-group. Furthermore, fertilization rates in the SPT-group were notably higher than those observed in the STR-group. Significantly, the best performances were obtained among eels in which at least 50% of oocytes were fully transparent at the time DHP was administered. We conclude that the fertility of eggs from spontaneously spawning eels is superior to that of eggs acquired by strip-spawning and artificial fertilization.
The aim of this work was to determine the effects of dark and light conditions on the E2, testost... more The aim of this work was to determine the effects of dark and light conditions on the E2, testosterone and thyroid hormones levels and on the gene expression levels (vitellogenin 1, vitellogenin 2, and estradiol receptor one) in European eels (Anguilla anguilla) during ovarian development induced by increasing doses of carp pituitary extracts (CPEs). The subjects were divided into 2 groups: 14-hour light:10-hour dark (Light Group) and 24-hour darkness (Dark Group). All the eels received intramuscular injections with CPE at a dosage of 10 mg/kg body weight (BW) once a week for the first 3 weeks, 20 mg/kg BW fourthsixth week, 30 mg/kg BW seventh-ninth week, and 40 mg/kg up to the end of the experiment (13th week). Vitellogenin and estradiol receptor expression levels did not show significant differences between the two housing conditions whereas in both groups vitellogenin mRNA increased starting from first CPE injection. Testosterone and 17-beta estradiol plasma levels were significantly greater in the Dark Group compared with the Light Group starting from the ninth and the 13th week, respectively. These results suggest that darkness could be a useful variable for standardizing gonadal maturation in eels kept in captivity.
Pituitary homogenate 11-Ketotestosterone dramatically affects ovarian physiology in previtellogen... more Pituitary homogenate 11-Ketotestosterone dramatically affects ovarian physiology in previtellogenic eels, notably increasing lipid accumulation and the expression of the follicle-stimulating hormone receptor. We therefore sought to combine androgen pre-treatment of female silver eels with "traditional" hypophysation in order to assess whether androgens constitute a valuable addition to induced spawning protocols. Eels were first implanted with different doses (0-30 mg) of 17-methyltestosterone to evaluate effects on oocyte size. Females (Trial I) were subsequently subjected to repeated injections with carp pituitary homogenate to artificially induce maturation. In a subsequent trial, we used 1 mg of androgen, implanted in either aromatizable (androstenedione) or non-aromatizable form (11-ketotestosterone) and again induced eels to mature artificially by repeated injections with carp pituitary homogenate. Androgen treatment significantly increased oocyte diameters prior to commencing carp pituitary homogenate treatment. Thereafter, less time, less money and less handling were required to reach the pre-ovulatory stage, while retaining comparable amounts of lipid in ovulated eggs. We contend that androgen pre-treatment has promise as a synchronizing and cost-effective measure for the artificial induction of maturation in anguillid eels.
European eels live most of their lives in freshwater until spawning migration to the Sargasso Sea... more European eels live most of their lives in freshwater until spawning migration to the Sargasso Sea. During seawater adaptation, eels modify their physiology, and their digestive system adapts to the new environment, drinking salt water to compensate for the continuous water loss. In that period, eels stop feeding until spawning. Thus, the eel represents a unique model to understand the adaptive changes of the enteric nervous system (ENS) to modified salinity and starvation. To this purpose, we assessed and compared the enteric neuronal density in the cranial portion of the intestine of freshwater eels (control), lagoon eels captured in brackish water before their migration to the Sargasso Sea (T0), and starved seawater eels hormonally induced to sexual maturity (T18; 18 weeks of starvation and treatment with standardized carp pituitary extract). Furthermore, we analyzed the modification of intestinal neuronal density of hormonally untreated eels during prolonged starvation (10 weeks) in seawater and freshwater. The density of myenteric (MP) and submucosal plexus (SMP) HuC/D-immunoreactive (Hu-IR) neurons was assessed in wholemount preparations and cryosections. The number of MP and SMP HuC/D-IR neurons progressively increased from the freshwater to the salty water habitat (control > T0 > T18; P < 0.05). Compared with freshwater eels, the number of MP and SMP HuC/D-IR neurons significantly increased (P < 0.05) in the intestine of starved untreated salt water eels. In conclusion, high salinity evokes enteric neuroplasticity as indicated by the increasing number of HuC/D-IR MP and SMP neurons, a mechanism likely contributing to maintaining the body homeostasis of this fish in extreme conditions.
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