The fine structures of mature spermatozoa were studied using TEM and SEM for 38 gobioid species, representing six families. Spermatogenesis was observed for three species. Gobioid spermatozoa were found to be exceptionally diversified, comprising most of the known teleostean sperm morphs. They were classified into 6 types based on a combination of morphological characters: Type I (20 species, including Rhyacichthys aspro)- Nucleus ovoidal to spherical, with distinct or indistinct hiatus in chromatin on lateral surface; single mitochondrion, located opposite chromatin in all but one species; single flagellum. Type II (8 species, including Sicyopterus japonicus)-Spherical nucleus without hiatus in chromatin; mitochondria numerous, in several longitudinal columns around base of flagellum; single flagellum. Type III (3 species of Odontobutidae and 4 species of Gobionellinae)-Nucleus spherical to cone-shaped; numerous, multilayered mi-tochondria; single flagellum. Type IV (Leucopsarion petersi)- Spherical nucleus with special anterior accessory; numerous irregularly-shaped mitochondria, around base of flagellum; two flagella. Type V (Ptereleotris hanae)- Nucleus bell-shaped, anteriorly attenuated; mitochondria numerous, spherical, around base of flagellum; single flagellum. Type VI (Schindleria sp.)- Nucleus elongate, cylindrical, pene-trated by flagellum to well beyond anterior tip; single mitochondrion enclosing fla-gellum at base; single flagellum. Comparison between these types and current gob-iod systematics revealed the following points: (1) Rhyacichthyidae and the two subfamilies of Eleotridae shared uniform sperm morphology within Type I.(2) Types IV, V and VI were distinct in having exceptional features.(3) Of six families of Gobioidei, Gobiidae has the most diversified sperm morphology. In addition, present grouping of sperm morphs was compared with gobioid phylogenies de-rived from molecular evidence. Results suggested that spermatozoa are potentially useful in evaluating the relationships within the Gobioidei.
The semen of Hemilepidotus gilberti, a non-copulatory marine cottid fish, includes two sperm types; eusperm for fertilization and parasperm, which cannot be employed in fertilization. A previous study having revealed the function of parasperm as antidispersive (reducing the lateral dispersion of semen) during semen transportation, the number of eusperm arriving at an egg mass was estimated so as to confirm the significance of parasperm function. Two simple models, one including and one excluding the size effect of the egg mass at ejaculation, were used. A considerable antidispersive effect was apparent when the egg mass was small, resulting in the latter being contained within the dispersion area of semen. When male H. gilberti emit semen, eggs that hang down from the genital opening do not extend beyond the semen dispersion area. Therefore, it was concluded that parasperm in this species ensures semen transportation and promotes fertilization success in males via an antidispersive effect related to egg mass size.
Mosquitofish, Gambusia affinis, repeat parturition at constant intervals under constant temperature and photoperiod. Although the intervals change with rearing condition, it is unclear whether or not environmental factors affect the process from vitellogenesis to parturition. To clarify the effects of temperature and photoperiod on the ovarian cycle (between ssuccessive parturition events), the parturition intervals and oocyte and embryonic development were investigated under various temperatures (20-31°C) and photoperiod (14-16 hr light-phase). The parturition intervals became shorter at higher temperatures under constant photoperiod. It is suggested that temperature primarily influences the rate of embryonic development; the effects being large at less than 25°C, and smaller at more than 25°C. The parturition intervals became shorter under long daylength periods at a constant temperature. It is suggested that photoperiod primarily affects the progress of vitellogenesis (timing of fertilization after parturition) and has little effect on embryonic development.
Population size and spawning site environment of the endangered southernmost population of Kirikuchi charr Salvelinus leucomaenis japonicus were investigated in a tributary on the upper reaches of the Totsu River system, Nara Prefecture, central Japan, in 2001. The total number of fish≥100 mm in fork length (FL) in May was estimated to be 308±50 (SE). Water depth and gravel size at spawning sites were 15±13 cm (meant±SD) and 31±8 cm, respectively. Spawn-ing sites were found mainly at upstream sites, freely accessible to the fish. The number of fish≥130 mm in FL had dropped in the lower section of the tributary in July, most probably as a result of leisure fishing. Spawning redds were clearly fewer in the lower sections than further upstream. These results indicated that fishing pressure on the population had been heavy, resulting in a decreased level of reproduction population.
A single specimen (IORD 76-1074, 287 mm in standard length) of an albulid fish, Albula glossodonta (Forssk51), collected by bottom gill net from Iriomote Island, Okinawa Prefecture, represents the first reliable record from Japan and the northernmost record of the species. Albula glossodonta is herein re-described and given a new Japanese name, “marukuchi-sotoiwashi.” The species is readily distinguishable from A. forsteri, previously known from Japan, as follows: anteriormost outline of lower jaw broadly rounded (vs. angular in the latter), shorter upper jaw length [2.8-3.3 (mean 3.1) times in head length vs. 2.6-2.9 (mean 2.8)] and molariform tooth plates in the oral cavity more broadly oval in shape (vs. more elongate).