In this study, the mean sperm concentration in goldfish
was higher than the values obtained for European hake
Merluccius merluccius [57] and lower than the values obtained
for perch [58] and rainbow trout [59], but similar to
those obtained for C carassius [60]. In carp, osmolalitydependent
permeabilization and structural changes are
induced in the sperm membrane by hyposmolality, and the
reorganization of the lipid structure has been proposed as a
possible mechanism [61]. The difference in Kþ ion concentration
(in salmonids) or osmotic pressure (in cyprinids,
clariids, and other families) between the seminal plasma
and water triggers the initiation of movement [62,63]. The
osmotic pressure seems to be the major controlling factor
in cyprinids [64].
In conclusion, dietary supplementation with 150 mg/kg
of astaxanthin improves osmolality, motility, fertilization
rate, and sperm concentration. This work provides novel
and informative data that could be used to devise the best
rearing conditions for male broodstock and the optimal
handling and storage of spermatozoa before fertilization.