The present study evaluated spermatozoal capacitation in Farfantepenaeus paulensis. This process has direct
applications in aquaculture, and it consists of the ionic, biochemical and morphological changes during the period
that the spermatophore is stored or adhered to the thelycum. These changes make the spermatozoa capable of
fertilization. The morphological changes of spermatozoal capacitation have been previously investigated only
in sicyoniids and open-thelycum penaeids. Thus, this study is the first morphological account of a closedthelycum
penaeid. F. paulensis broodstock were captured offshore in southern Brazil, and spermatophores
were collected from the terminal ampoule and from the thelycum of sexually mature females that had naturally
copulated. The ultrastructure of the spermatozoal capacitation was investigated via transmission electron microscopy.
Spermatozoa of F. paulensis show the following changes related to capacitation: (1) the chromatin became
less condensed; (2) the acrosomal region became more electron-dense (3) the acrosomal cap became less
concave; and (4) the subacrosomal region became much more electron-dense. These results demonstrate that
the morphological changes in capacitated spermatozoa of F. paulensis are similar to those previously reported
for open-thelycum penaeids, i.e., Litopenaeus species. Further studies on the capacitation process are required, especially
to evaluate the interaction between biochemical and morphological changes. Such research could be useful
for developing biotechnologies that will allow spermatozoal induction without storing the spermatophore in
the thelycum and therefore allow in vitro larval production.