ACROSOME-LIKE STRUCTURES IN THE SPERMATOZOA OF TELEOST FISHES

The spermatozoa of teleost fishes lack an acrosome. However, peculiar structures have been described at the front of the nucleus in some spe cies, and these take various forms. One or more vesicles may be placed at the front of spermatid nucleus and, in some cases, may be retained in the spermatozoon The anterior nuclear envelope may exhibit densifi cation or intermembraneous differentiation. Stacks of membranes may be apposed to the nuclear envelope. No acrosome has been unambiguously i dentified to date in the spermatozoon of any teleost. The acrosome has been lost in the Teleostei during evolution, though some species have retained traces of it at the front of the germ cells. Thus, vestiges of acrosomal vesicles remain in Gambusia affinis. Lepadogaster lepadog aster, and Oncorhynchus mykiss. There is also a subacrosomal type of d ifferentiation of the nuclear envelope in some spermatozoa. Similar st ructures have been described in the Porifera and Cnidaria, groups of p rimitive Metazoa in which the acrosome first evolved.