chapter 3 - RiuNet

GENERAL DISCUSSION
sperm motility patterns and the period of fertility (Billard, 1978). However,
our data has shown that sperm motility parameters do not improve when
using partly diluted seawater in pufferfish, so the common activation
medium (not diluted seawater) is recommended when carrying out
reproduction trials in this species.
Regarding the ion composition of the activation media, we have reported
that despite the fact that pufferfish spermatozoa were able to initiate
movement without any ion in the activation medium, the
presence/absence of Ca 2+ and K + affected kinetic parameters such as
velocities. We also observed that spermatozoa velocities (VCL, VSL and VAP)
were highly correlated to the fertilization success and hatching rates. It can
therefore be assumed that the presence of these ions in the activation
media helps the fertilization process, thus the proper ion composition of
the activation/fertilization media should be taken into account in order to
reach suitable fertilization and hatching rates in both laboratory trials and
commercial hatcheries.
However, while in the majority of marine fish species studied sperm
motility can be induced by hyperosmotic non-ion solutions (using sugars,
i.e.), in species such as tilapia (Oreochromis mossambicus) certain ions such
as calcium are essential for sperm activation (Linhart et al., 1999). Thus, it
seems clear that there is a wide interspecific variability in terms of the role
of extracellular ions and their effect on the sperm motion parameters, so
more studies focusing this topic are necessary in order to understand the
sperm motility activation process in marine fish.
On the other hand, although it is widely accepted that firstly, the
osmolality, and secondly, the ion composition of the activation media are
the main factors triggering sperm motility in marine fish, little is known
about the molecular mechanisms that enable environmental stimuli to
determine the activation of the axoneme and the intracellular ion changes
occurring after sperm activation (Zilli et al., 2012). In this thesis we have
reported that when using an ion-rich medium (seawater) for activation of
the sperm, intracellular Ca 2+ and K + increased both in European eel and
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