Sperm and Spermatozeugma Ultrastructure in the Inseminating Catfish, Trachelyopterus lucenai (Ostariophysi: Siluriformes: Auchenipteridae)
This study presents details of the ultrastructure of the spermatozeugmata and spermatozoa of the South American catfish, Trachelyopterus lucenai, an inseminating species. Spermatozoa are tightly packaged into unencapsulated bundles, spermatozeugmata, with as many as 130 cells comprising a single packet. Within an individual spermatozeugma, cells are aligned side by side such that the anterior region of the bundle is comprised of nuclei, the middle region midpieces, and the posterior region flagella. Integrity of the packet appears to be maintained by specialized junctions between adjacent cells along their entire lengths. Each spermatozoon is characterized by an elongate nucleus containing condensed chromatin and a fossa at the posterior end. The elongate midpiece contains multiple mitochondria, abundant glycogen deposits, and accessory microtubules that run along the length of the midpiece. The ultrastructural modifications of the spermatozoa are discussed as possible adaptations associated with the reproductive mode of insemination.Abstract
Transmission electron micrographs of sections through successively more posterior regions of spermatozeugmata from a semen sample of a mature male Trachelyopterus lucenai of SL 147 mm. (A) Anterior region through nuclei. (B) More posterior region through nuclei. (C) Section through anterior midpiece region. (D) Section through more posterior midpiece region. (E) Section through flagella. Bar = 2 μm
Transmission electron micrographs of sections through successively more posterior regions of spermatozoa within spermatozeugmata from a semen sample of a mature male Trachelyopterus lucenai of SL 147 mm. Symbols: c, cytoplasmic canal of cytoplasmic collar; f, nuclear fossa; m, mitochondrion; n, nucleus; arrowheads, accessory microtubules; white arrows, glycogen deposits; black arrows, junctions between adjacent spermatozoa. (A) Anterior section through nucleus. (B) Posterior region of the nucleus through nuclear fossa. (C) Anterior midpiece region. (D) Midpiece region with attached cytoplasmic collar containing the flagellum. (E) Midpiece region at the opening of the cytoplasmic collar. (F) Posterior region of midpiece; free flagellum is also seen. Bar = 0.2 μm
Transmission electron micrographs of longitudinal sections through spermatozoa within spermatozeugmata from a semen sample of a mature male Trachelyopterus lucenai of SL 147 mm. Symbols: N, nucleus; arrowheads, opening of cytoplasmic collars; arrow, glycogen deposit. (A) Sections through the posterior nucleus and anterior midpiece regions showing the flagella initially contained within cytoplasmic collars. (B) Sections through the greatly elongated nuclei. Bar = 0.5 μm