Ultrastructural observations of eu‐ and paraspermiogenesis in the cottid fish Hemilepidotus gilberti (Teleostei: Scorpaeniformes: Cottidae)

Abstract

The developmental process of eu- and paraspermatozoa in the cottid fish, Hemilepidotus gilberti, was observed by electron microscopy. Euspermatozoa of H. gilberti consist of a thin disk-like sperm head (about 3 microm in length), a short middle piece, and a long flagellum, but lack an acrosome. On the other hand, during spermiogenesis, aberrant spermatids, rich in cytoplasm and possessing binuclei, develop into cysts containing spermatids. The developing aberrant spermatids connect with normal spermatids and euspermatozoa by intercellular bridges. The early phase of chromatin condensation in aberrant spermatids is almost identical to that in normal spermatids, but the nuclei in the later phase develop into a mass of highly electron-dense globules. Since the aberrant spermatids complete karyokinesis but not cytokinesis at telophase of the second meiotic division, they are considered to develop into hyperpyrenic cells due to incomplete cytokinesis of the second meiotic division. These spermatids are oval in shape (5-7 microm in diameter) and lack a flagellum. The aberrant spermatids of H. gilberti are shed along with euspermatozoa and amount to about 50% of semen in volume. Judging from their form and developmental process, aberrant spermatids produced in H. gilberti are considered hyperpyrenic paraspermatozoa.

Parasperm: morphological and functional studies on nonfertile sperm

“…Generally, cleavage furrows occur at telophase after karyokinesis in animal cells (Rhodin, 1974). However, some germ cells in each cyst at telophase of the second meiotic division in H. gilberti do not form cleavage furrows, suggesting that cytokinesis does not complete, although the two daughter nuclei reconstruct most of the nuclear membrane (Hayakawa et al, 2002b;Fig . 7A).…”

“…In the course of spermatogenesis in cottoid fi sh, no feature indicating the initiation of divergence to the parasperm line from the normal line is observed in germ cells before meiosis. However, aberrant spermatids, which differ from normal euspermatids morphologically, appear after Yamashiki and Kawamura (1997) and Kawamura et al (2000)] the second meiotic division in every cyst (Hayakawa et al, 2002b). Generally, cleavage furrows occur at telophase after karyokinesis in animal cells (Rhodin, 1974).…”

“…A noncopulatory marine species, Hemilepidotus gilberti, is known to produce parasperm (Hayakawa et al, 2002b). The parasperm of this fi sh are oval in shape, being 5-7 µm in diameter.…”

“…Devel- Hayakawa et al (2002b).] Bars A 10 µm; B, D 5 µm; C, E 1 µm opment of the aberrant spermatid in the freshwater cottoid fi sh Cottus hangiongensis involves an incomplete second meiotic division in which the nucleus usually divides into two daughter nuclei, although the cytoplasmic division does not occur .…”

“…It is considered to act as the regulator to transport materials required for the reconstruction of chromosomes (Meithing, 1990). Thus, the bridge-partitioning complex may more or less participate in the development of parasperm in cottoid fi sh to determine alternative pathways for the development of germ cells as either eusperm or parasperm within the cyst (Hayakawa et al, 2002b).…”