Sperm-cell ultrastructure of north american sturgeons. IV. The pallid sturgeon (Scaphirhynchus albus Forbes and Richardson, 1905)

Sperm-cell morphology and ultrastructure in the pallid sturgeon (Scaphirhyn chus albus) were examined using transmission and scanning electron microsco py. Metrics and structure were compared with similar metrics obtained from other published descriptions of sturgeon sperm cells. General morphology wa s found to be similar to that of sperm cells of the white (Acipenser transm ontanus), lake (A. fulvescens), stellate (A. stellatus), Chinese (A. sinens is), Russian (A. gueldenstaedti colchicus), and shortnose (A. brevirostrum) sturgeons, which all shared a gradual tapering of the nuclear diameter fro m posterior to anterior, unlike that of the Atlantic sturgeon (A. oxyrhynch us). The sperm cell of the pallid sturgeon was similar in size to that of t he Atlantic sturgeon, being only slightly larger. The sperm cell of the pal lid sturgeon differed from those of other sturgeons chiefly in the acrosoma l region, where the posterolateral projections (PLP) have the shape of an a cute triangle and are arranged in a spiral about the longitudinal axis of t he cell. The PLP were longer than those of other sturgeons, being twice the length of those of the Atlantic sturgeon and 58% longer than those of the lake sturgeon. Also, in cross section the acrosome had the shape of a hollo w cone rather than the cap of an oak tree acorn, as was found in ultrastruc tural studies of other sturgeons. In addition, we were able to confirm that the structural arrangement of the distal centriole of the midpiece is iden tical with that of the proximal centriole: nine sets of microtubular triple ts around the periphery of the centriole. This information is of potential use to fishery biologists, forensic biologists, zoologists, reproductive ph ysiologists, taxonomists, evolutionary biologists, and aquaculturists.