“…In European eel, several researchers have developed different sperm cryopreservation protocols (Asturiano et al, 2003;Herranz-Jusdado et al, 2019a;Müller et al, 2004;Peñaranda et al, 2009;Szabó et al, 2005). Moreover, cryopreserved European eel sperm have been successfully used in fertilization trials (Asturiano et al, 2016) and in hybridization trials with Japanese eel (Anguilla japonica) eggs (Müller et al, 2012;, although an increased rate of larval deformities were observed when fertilizing with cryopreserved sperm (Müller et al, 2018), evidencing the need of refinement of the protocols. Recently, Herranz-Jusdado et al (2019a) have compared the available European eel cryopreservation protocols with the aim of choose the most efficient one and standardize its use, but this protocol still consists of small volumes of 0.5 mL, which is impractical for large-scale fertilization programs needed in e.g.…”