Chapter 14 Improvements on the Reproductive Control of the European Eel

Asturiano, Juan F.

doi:10.1007/978-981-15-2290-1_15

Cited by 7 publications

(6 citation statements)

References 122 publications

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“…Despite intensive research efforts (reviewed by Palstra and van den Thillart, 2009 ; Mordenti et al, 2019 ; Tomkiewicz et al, 2019 ; Asturiano et al, 2020 ), the life cycle of European eel in captivity is still not closed. In our facilities, we simulate life cycle events to cover the trajectory from wild juvenile glass eel up to larval production.…”

Section: Introductionmentioning

confidence: 99%

Steroid implants for the induction of vitellogenesis in feminized European silver eels (Anguilla anguilla L.)

et al. 2022

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Assisted propagation of the European eel will lead to a closed production cycle supplying the aquaculture industry with juvenile glass eels. Females require long-term weekly treatment with pituitary extract (PE), which is stressful and causes abnormalities in oogenesis. We tested the effects of 17α-methyltestosterone (17 MT), as potent androgen activating the androgen receptor, and 17β-estradiol (E2), as an inducer of vitellogenesis, to shorten the duration of PE treatment.Four groups of feminized eels were subjected to a simulated migration and subsequent injection with implants containing 17 MT (17 MT-group), E2 (E2-group) or 17 MT plus E2 (17 MT + E2-group) to test for synergistic effects, or without any steroids as controls (C-group). The effects of a 2-months treatment were investigated by determining the eye index (EI), hepatosomatic and gonadosomatic index (HSI and GSI, respectively), plasma steroid concentrations by liquid chromatography mass spectrometry (LCMS), gonadal histology, expression of androgen receptors a and b (ara, arb); estrogen receptor 1 (esr1); FSH receptor (fshr); vitellogenin receptor (vtgr) and aromatase (cyp19), and the required number of weekly PE injections to fully mature. For many parameters, both the 17 MT and E2 groups showed an increase vs. controls, with the 17 MT + E2 group showing a synergistic effect, as seen for EI, GSI (3.4 for 17 MT and for E2, 6.6 for 17 MT + E2), oocyte diameter and ara, arb and esr1 expression. Concentrations of almost all focal steroids decreased with simulated migration and steroid treatment. Only eels of the 17 MT-group showed increased expression of cyp19 and of fshr, while fshr expression increased 44-fold in the 17 MT + E2 group, highlighting that co-implantation is most effective in raising fshr mRNA levels. Specific for eels of the E2 groups were vitellogenesis-associated changes such as an increase of HSI, plasma E2, and presence of yolk in the oocytes. Steroid treatments reduced the duration of PE treatment, again synergistically for co-implantation. In conclusion, E2 is necessary to start vitellogenesis, but 17 MT has specific effects on cyp19 and fshr expression. The combination is necessary for synergistic effects and as such, steroid implants could be applied in assisted reproduction protocols for European eel to improve oocyte quality leading to the production of more vital larvae.

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Section: Introductionmentioning

confidence: 99%

Steroid implants for the induction of vitellogenesis in feminized European silver eels (Anguilla anguilla L.)

et al. 2022

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“…Overfishing, habitat reduction, pollution, and the swimbladder parasite (Anguillicola crassus) are some of the causes that have led to the decline of the European eel [2]. As a result, it was included in the Red List of the International Union for Conservation of Nature (IUCN) as a "Critically Endangered" species [3], and measures for the recovery of the stock have been established by the European Union (Regulation 1100/2007, 18 September 2007) [4].…”

Section: Introductionmentioning

confidence: 99%

“…The European eel is a catadromous fish with a very complex life cycle, which includes two transoceanic migrations. In order to overcome the lack of natural spawning stimuli in captivity, the sexual maturation of both males and females must be induced with long-term hormonal treatments [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Using Osmotic Pumps to Induce the Production of Gametes in Male and Female European Eels

Blanes-García

García-Salinas

Morini

et al. 2022

Animals

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The European eel (Anguilla anguilla) is a commercially valued species for aquaculture. Over the past decades, it has experienced a drastic reduction in its natural stocks. Thus, breeding in captivity is considered essential, nowadays, to guarantee the eel aquaculture and to reduce pressure on natural populations. Traditionally, the European eel has been sexually matured by means of weekly hormonal injections, which cause stress to the fish. The purpose of this research study was to assess the use of osmotic pumps as a new method to induce sexual maturation in male and female European eels, without the weekly injection. The control groups were treated with weekly hormone injections (recombinant human chorionic gonadotropin for males and carp pituitary extract for females), and the implanted groups were treated with osmotic pumps (ALZET® osmotic pumps) loaded with the respective hormones. Regarding male European eels, this study shows that the use of controlled release systems was able to induce the maturation and spermiation, but without the necessary capacity to produce enough gametes with acceptable quality parameters that could meet the needs of a commercial eel hatchery. Concerning female European eels, the study demonstrates that the use of osmotic pumps loaded with CPE became an effective method, generating early maturations (4 to 10 weeks) in 50% of the females, so this method could become a viable alternative for eel hatchery procedures.

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“…Together, this has led to increased efforts in closing the life cycle of European eel in captivity, in the attempt to relieve the pressure from fisheries and to develop a sustainable aquaculture, which is also happening to the closely related anguillid species, the Japanese eel Anguilla japonica [ 17 ]. New advancements in induced sexual maturation have led to the development of effective assisted reproduction strategies using hormonal treatments to induce gamete development [ 18 – 20 ] in European eel, enabling production of viable embryos and larvae entering the feeding larval stage [ 21 , 22 ]. In the attempt to mimic the natural conditions during reproduction experiments, as a common and consolidated practice eels are not fed.…”

Section: Introductionmentioning

confidence: 99%

Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: What happens to the liver?

Bertolini

Jørgensen²,

Henkel³

et al. 2020

PLoS ONE

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The life cycle of European eel (Anguilla anguilla), a catadromous species, is complex and enigmatic. In nature, during the silvering process prior to their long spawning migration, reproductive development is arrested, and they cease feeding. In studies of reproduction using hormonal induction, eels are equivalently not feed. Therefore, in female eels that undergo vitellogenesis, the liver plays different, essential roles being involved both in vitellogenins synthesis and in reallocating resources for the maintenance of vital functions, performing the transoceanic reproductive migration and completing reproductive development. The present work aimed at unravelling the major transcriptomic changes that occur in the liver during induced vitellogenesis in female eels. mRNA-Seq data from 16 animals (eight before induced vitellogenesis and eight after nine weeks of hormonal treatment) were generated and differential expression analysis was performed comparing the two groups. This analysis detected 1,328 upregulated and 1,490 downregulated transcripts. Overrepresentation analysis of the upregulated genes included biological processes related to biosynthesis, response to estrogens, mitochondrial activity and localization, while downregulated genes were enriched in processes related to morphogenesis and development of several organs and tissues, including liver and immune system. Among key genes, the upregulated ones included vitellogenin genes (VTG1 and VTG2) that are central in vitellogenesis, together with ESR1 and two novel genes not previously investigated in European eel (LMAN1 and NUPR1), which have been linked with reproduction in other species. Moreover, several upregulated genes, such as CYC1, ELOVL5, KARS and ACSS1, are involved in the management of the effect of fasting and NOTCH, VEGFA and NCOR are linked with development, autophagy and liver maintenance in other species. These results increase the understanding of the molecular changes that occur in the liver during vitellogenesis in this complex and distinctive fish species, bringing new insights on European eel reproduction and broodstock management.

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Chapter 14 Improvements on the Reproductive Control of the European Eel

Cited by 7 publications

References 122 publications

Steroid implants for the induction of vitellogenesis in feminized European silver eels (Anguilla anguilla L.)

Steroid implants for the induction of vitellogenesis in feminized European silver eels (Anguilla anguilla L.)

Using Osmotic Pumps to Induce the Production of Gametes in Male and Female European Eels

Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: What happens to the liver?

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