| Summary: | Trabajo presentado en la International Conference & Exposition Aquaculture Europe, celebrada en Funchal, Maderia (Portugal) del 04 al 07 de octubre de 2021. [Introduction]: The European eel (Anguilla anguilla) is a highly valued species targeted for aquaculture production. However, it 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). It 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 of 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, ...
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