Effects of cold seawater pre-treatments on
induction of early sexual maturation and sperm production in European eel (Anguilla
anguilla)
Leonor Ferrão, Marina Morini, Wendy A. González-Lopéz,
Victor Gallego, Alicia Felip, Luz Pérez, Juan F. Asturiano
Abstract
To induce sexual maturation in captivity, eels rely on hormonal
treatments, but this process is costly and time-consuming. As an alternative,
different types of conditioning, also referred as pre-treatment, have been
assessed to ease hormonal treatment response. Recent studies have shown that
migrating eels experience a wide range of temperatures, varying from 12 °C at
night to as low as to 8 °C during the day. Therefore, this study evaluates the
effects of low-temperature (10 °C) seawater pre-treatments of different
durations (2 and 4 weeks) on male eel reproduction. The eye, gonadosomatic and
hepatosomatic indexes from control (without thermic seawater pre-treatment) and
pre-treated fish were measured. Blood and testis samples were also collected
for sex steroid and histology analysis, respectively. Eels pre-treated for 2
weeks demonstrated increased progestin levels, comparing with the control
group. Eels pre-treated for 4 weeks showed significantly higher gonadosomatic
index and elevated androgens and estradiol levels in comparison with the
remaining groups. In eels pre-treated for 2 and 4 weeks, there was an increase
in the proportion of spermatogonia type B cells compared to undifferentiated
spermatogonia type A, a differentiation process that was not observed in the
control group. Cold seawater pre-treatment induced early sexual maturation,
including steroid production, which consequently stimulated biometric changes
and increased spermatogonia differentiation. Following the pre-treatments, eels
started receiving standard hormonal treatment (with recombinant human chorionic
gonadotropin at 20 °C). Pre-treated males started to spermiate earlier than the
control group. In some treatment weeks, pre-treated individuals registered
higher values of sperm density, motility, and kinetic parameters. Moreover, an
economic evaluation was carried out relating the investment made in terms of
hormone injections with the volume of high-quality sperm obtained from each
experimental group. The low temperature pre-treatments demonstrated their
economic effectiveness in terms of hormone treatment profitability, increasing
the production of high-quality sperm in the European eel. Thus, this in vivo
study suggests that cold seawater pre-treatment may increase sensitivity to the
hormone applied during standard maturation treatment.
Doi: https://doi.org/10.1007/s10695-024-01402-w (Open access)
