The role of acrosin-like activity in reproductive biology of Acipenserid fish may be related to the function of male gametes and fertilization process. Acrosin may participate in acrosome reaction (as in mammals,) and penetration of egg envelopes. The latter function of acrosin as a sperm lysine is puzzling, considering presence of egg’s micropyles. However, in Acipenserid fish a delay in fertilization is possible, due to prolonged viability of sturgeon gametes in freshwater. Therefore there may be a need for sperm lysin action, because longer contact of oocytes with water may cause obstruction of micropyle by jelly coat. This hypothesis proposed by S.I. Doroshov may explain why acrosin-like activity was retained on spermatozoan of Acipenserid fish, despite the presence of micropyles in egg.