Aquaculture Europe 2021

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Add To Calendar 05/10/2021 11:30:0005/10/2021 11:50:00Europe/LisbonAquaculture Europe 2021COLD SEAWATER PRE-TREATMENT AFFECTS THE SPERMATOGENESIS AND THE REPRODUCTIVE PERFORMANCE OF MALE EUROPEAN EELSCongress AuditoriumThe European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982

COLD SEAWATER PRE-TREATMENT AFFECTS THE SPERMATOGENESIS AND THE REPRODUCTIVE PERFORMANCE OF MALE EUROPEAN EELS

 L. Ferrãoa* , M. Morinia , V. Gallegoa , A. Felipb ,  A. Gómezb , L. Péreza and J.F. Asturianoa

 

a  Grupo de Acuicultura y Biodiversidad.  Instituto de Ciencia y Tecnología Animal.  Universitat Politècnica de València. Camino de Vera s/n, 46022 Valencia, Spain. Email: jfastu@dca.upv.es

b Department of Fish Physiology and Biotechnology, Instituto de Acuicultura Torre de la Sal (IATS), CSIC, Ribera de Cabanes, 12595 Castellón, Spain.

 



Introduction

The European eel (Anguilla anguilla) is a  highly  valued  species  targeted for aquaculture production . However, i t is considered  a  critically endangered  species by CITES , and  reproduction in captivity seems to be the only realistic  alternative  to  solve  both  economic and ecological  problems (Asturiano, 2020). I t is possible to obtain gametes  for artificial fertilization but  it requires hormonal treatment , which  is  a time- consuming  and expensive  process (Gallego et al., 2012). Moreover ,  the  variable response to these treatments  results in  high mortality rates during  the  early stages  of development, which  could be caused (at least in part )  by  low sperm quality and uncontrolled epigenetic factors (Herráez et al., 2017) .  Considering the  environmental  conditions  experienced during eels  oceanic migration, the effects of  low temperature  combined with hormonal treatment have been used  to  better understand the onset o f  eel maturation (Peñaranda et al., 2016). Thus , the  present  study  considers  the  use of low temperature as a pre-treatment  before  starting a standard hormonal treatment and evaluates its impact on  eel  maturation and male reproductive performance.

Material and Methods

 Eighty-eight  male European eels were maintained for 3-4 days in freshwater at 20 ºC .  Then, 6  males were sacrificed , as initial control, and the rest were changed to seawater at 10 ºC ,  except  the  control group,  which  was changed to seawater but maintained at 20 ºC.  Low water temperature pre-treatments were applied  during 1, 2  or 4 weeks to groups of 20 males. Once finished each pre-treatment, 8 fish per group were sacrificed for sampling. The temperature of the water of the remaining males was increased to 20 ºC in 3-4 days and they started receiving standard hormonal treatment ( weekly administration of  recombinant  chorionic  human gonadotropin , rhCG ; Ovitrelle, Spain, 1.5 IU/g fish) . From sacrificed fish (controls and pre-treated) biometric parameters were measured. Blood and testis samples were used to perform steroid (T, 11- KT and E2) analyses and histology, respectively.  Once eels were spermiating , sperm volume , motility and kinetic parameters  were evaluated  weekly  using a CASA system.

Results

The eye , fin and hepatosomatic indexes from 1-week, 2- and 4-weeks pre-treated  fish  were significantly higher than those of the control group.  The gonadosomatic indexes registered in the control group  were  unusually high and significantly differed with 1-week pre-treatment group  but not with the 2- and 4-weeks  groups.  Androgen  levels (T, 11- KT)  were significantly higher after 4-week s of pre-treatment in comparison with  the control.  The E2 levels  did not show the same increasing profile.  The control and 1-week pre-treated males  showed significantly higher  percentages of undifferentiated and differentiated  type A  spermatogonia  in comparison with  early  spermatogonia type B .  The males after 2- and 4-weeks of pre-treatment revealed  a  significantly  increased proportion  of differentiated spermatogonia type A.  After the rhCG treatment, males from the 4-weeks pre-treatment group started to produce sperm earlier than males from the other groups. The s perm  volume in  the 4-weeks pre-treatment group increased during the first weeks of spermiation  and  in the control group  at  the  end  of the experiment, but no significant differences were found. Sperm motility  and  kinetics parameters  were low in pre-treated groups  throughout the whole experiment while in the control group  increased significantly at  the end  of the hormonal treatment.

Discussion

 The onset of maturation in the European eel is controlled by environmental conditions found during their migration. The application of pre-treatments can be important to induce maturation in aquaculture eels, which do not encounter these conditions  (Palstra and van den Thillart , 2009).  Several factors such as temperature, salinity, forced  swimming and pressure have been used as part of pre-treatments applied to eels (reviewed by Asturiano et al., 2020).  Rozenfeld et al. (2019)  evaluated  the effects  of cold seawater  in European eel  maturation without hormonal treatment . In eels treated at 10 ºC, the T and 11-KT levels were  higher and there was an increase in the proliferation  of  differentiated  type A spermatogonia .  Our results also corroborate that low- temperature pre-treatment (4- weeks at 10 °C)  induces an early sexual development, thus leading to the release of androgens which  promote the proliferation of  type A spermatogonia .  However, the low sperm quality found in  the pre-treated groups revealed that thermal pre-treatment followed by rhCG  treatment at high temperatures  impairs spermatogenesis. Low-temperature pre-treatments induce testis cell proliferation and synchronization but inhibit further maturation.  Peñaranda et al. (2016)  suggested that low  seawater temperature inhibits the gene expression of enzymes responsible for the synthesis of  maturation-inducing steroids (MIS) during  eels oceanic migration. Thus, the premature maturation of the testis is  prevented before eels arrive to the spawning areas and a temperature threshold is re ached allowing the change of the steroidogenic pathway  to change from androgens to MIS . In our experiment, low- temperature pre-treated males had a time-dependent and fast response to rhCG treatment ( in comparison with  control  males  maintained at 20 °C), but their spermiation period was shorter and the ir sperm motility parameters  were  significantly lower. If this is evidencing a lower rate of gene expression in the testis,  and thus limiting the final sperm maturation process,  is an open question that requires further research.

Bibliography

 Asturiano, J.F., 2020. Improvements on the reproductive control of the European eel, in: Yoshida, M., Asturiano, J.F. (Eds.),  in: Reproduction in Aquatic Animals: From Basic Biology to Aquaculture Technology. Springer Nature, Singapore, pp. 293-320.

Gallego, V., Mazzeo, I., Vílchez, M.C., Peñaranda, D.S., Carneiro, P.C.F., Pérez, L., Asturiano, J.F., 2012. Study of the effects of thermal regime and alternative hormonal treatments on the reproductive performance of European eel males (Anguilla anguilla ) during induced sexual maturation. Aquaculture 354-355, 7-16.

 Herráez, M.P., Ausió , J., Devaux , A., González-Rojo, S., Fernández-Díez, C., Bony, S., Saperas, N., Robles, V., 2017. Paternal contribution to development: Sperm genetic damage and repair in fish. Aquaculture 472, 45- 59.

 Palstra, A., van den Thillart , G., 2009.  Maturation and Reproduction, in: van den Thillart , G., Dufour, S., Rankin, J.C. (Eds.), Spawning Migration of the European Eel - Reproduction Index, a Useful Tool for Conservation Management. Springer, pp. 253-278.

 Peñaranda, D.S., Morini, M., Tveiten , H., Vílchez, M.C., Gallego, V., Dirks, R.P., van den Thillart , G.E.E.J.M., Pérez, L., Asturiano, J.F., 2016. Temperature modulates the testis  steroidogenesis in European eel. Comp. Biochem . Physiol. A 197, 58–67.

Rozenfeld, C., García-Carpintero, V., Pérez, L., Gallego, V., Herranz-J usdado, J.G., Tveiten, H., Johnsen, H.K., Fontaine, R., Weltzien, F.A. , Cañizares , J., Asturiano, J.F., Peñaranda, D.S., 2019. Cold seawater induces early sexual developmental stages in the BPG axis of European eel males. BMC Genomics 20: 597.