Characteristics of Muskellunge Spermatozoa I: Ultrastructure of Spermatozoa and Biochemical Composition of Semen

Abstract

We investigated the ultrastructure of spermatozoa and some physiological and biochemical parameters of semen in muskellunge Esox masquinongy. Ultrastructure of spermatozoa analyzed with scanning and transmission electron microscopes revealed a spherical head, 1.5 um in diameter. Unlike the spermatozoa of other teleost fishes, an elongated midpiece with abundant mitochondria was found to be characteristic for muskellunge spermatozoa. Three techniques for measuring sperm concentration, counting with a hemacytometer, spermatocrit, and spectrophotometric methods, provided similar results (19.7 ± 6.1 × 109 sperm/mL). The spectrophotometric method is recommended because it is rapid and requires only small amounts of semen. Ionic concentrations and osmolality (289 ± 16.8 milliosmols/kg) of seminal plasma were reported. Sodium (129 ± 6.7 mM) and potassium (27.88 ± 3.27 mM) concentrations were closer to levels found in the seminal plasma of salmonids than cyprinids. Aspartate aminotransferase (AspAT) activity was measured with and without supplement of pyridoxal phosphate (PLP) from sperm extracts. A 96% increase of AspAT was found when PLP was included in the assay. We confirmed the presence of antiproteinase activity (against cod trypsin) in seminal plasma of muskellunge. Using the flow cytometry method, we estimated that the DNA stainability of muskellunge spermatozoa was 0.188 ± 0.008 times that of red blood cells (TRBC) from diploid rainbow trout Oncorhynchus mykiss. The DNA stainability of muskellunge spermatozoa was significantly lower than that of muskellunge embryonic cells, which was 0.474 times that of the TRBC (2.21 pg DNA/cell, based on the internal standard of TRBC of 4.66 pg DNA/cell).