Facultatively internal fertilization and anomalous embryonic development of a non-copulatory sculpin Hemilepidotus gilberti Jordan and Starks (Scorpaeniformes: Cottidae)

Ovarian inseminated sperm impacts spawning success in zebrafish, Danio rerio (Hamilton, 1822) even in the absence of a male stimulus

Reproductive obstacles have led scientists to develop novel techniques/technologies for artificial reproduction. We aimed to investigate the possibility of propagating zebrafish females using sperm ovarian lavage with and without presence of male stimulus. This experiment consisted of several treatments: traditional spawning approaches with females and wild-type males (AB♀ × AB♂); no males present with non-manipulated females (AB♀); no males present with females inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)]; no males present with females inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)]; non-manipulated females kept separately from wild-type males (AB♀|AB♂); females kept separately from wild-type males and inseminated with NaCl into ovarian lobes [AB♀(inj.NaCl)|AB♂]; and females kept separately from wild-type males and inseminated with sperm from transgenic males into ovarian lobes [AB♀(inj.Tg♂)|AB♂]. There were no released eggs in both negative control treatments (AB♀ and AB♀|AB♂). Egg production increased (ranged from 0 to 28.5 eggs/female) when females were injected in the presence [AB♀ (inj.NaCl) |AB♂] or absence of male stimulus [AB♀ (inj.NaCl) and (AB♀(inj.Tg♂)]. A further increase in egg production [relative to AB♀, AB♀ (inj.NaCl), and AB♀|AB♂] was detected when females were inseminated with pooled sperm from transgenic males in the presence of male stimulus [AB♀(inj.Tg♂)|AB♂; ranged from 2.5 to 55 eggs/female] or when using traditional spawning approaches (AB♀ × AB♂; ranged from 25 to 131 eggs/female). Females inseminated with sperm produced embryos, although no differences were detected when females were inseminated with pooled sperm from transgenic males in presence (11.8 ± 16.3%) or absence (average = 12.6 ± 9.2%) of male stimulus. Traditional spawning approaches produced the most eggs (81.2 ± 42.3 per female) and highest fertilization rate (81.3 ± 10.4).

Internal embryonic development in a non-copulatory, egg-laying teleost, the three-spined stickleback, Gasterosteus aculeatus

The switch from egg-laying to retaining and giving birth to live young is a major transition in the history of life. Despite its repeated evolution across the fishes, records of intermediate phenotypes are vanishingly rare, with only two known cases in existence of normally egg-laying fish species retaining embryos within the ovaries. We report the discovery of a third occurrence, in which well-developed embryos were found in the ovaries of a three-spined stickleback (Gasterosteus aculeatus), a non-copulatory, normally oviparous species. Extracted from the parent fish, these embryos hatched and grew to adulthood. Genetic and physiological examination of the parent fish and offspring ruled out development by parthenogenesis and hermaphroditism, therefore implicating internal fertilisation by a male stickleback. This extremely rare phenomenon may have been facilitated in this population by an unusual tendency for females to become egg-bound, and suggests that some major transitions may arise almost spontaneously.

Ontogenesis from embryo to juvenile and salinity tolerance of Japanese devil stinger Inimicus japonicus during early life stage

Embryonic development and morphological characteristics of Japanese devil stinger Inimicus japonicus during early life stage were investigated. Larvae were hatched out 50 h after fertilization at temperature 21°C. Total length of the newly hatched larva was 4.03 mm, the mouth of the larva opened at 3 days after hatching (DAH), and the yolk sac of the larva disappeared at 5 DAH. After hatching, the pectoral fin first developed, then the tail fin, dorsal fin, anal fin and pelvic fin continuously developed, and all fins formed completely at 15 DAH. The metamorphosis was complete at 25 DAH, and the body color and habit of the metamorphosed individuals were different from the larvae. At 30 DAH, the morphology and habit of the juveniles were the same to adults. In order to determine the suitable salinity for larviculture of I. japonicus, salinity tolerance at different early developmental stages was compared in terms of the survival activity index (SAI) and mean survival time (MST). The results indicated that salinity tolerance varied with development stages. The optimum salinity range for newly hatched larvae was 10-25‰. Larvae showed low tolerance to low salinity (5‰) before the mouth opened, and the suitable salinities for the larvae with open mouth, yolk-sac larvae, post yolk-sac larvae were 10-15‰. The flexion larvae showed a wider salinity tolerance with range of 5-20‰. After metamorphosis, the juveniles showed a preferable adaptability of salinities of 15-20‰. The SAI and MST of individuals at various stages under different salinity conditions were positively correlated.

Sperm storage and motility in the ovary of the marine sculpin Alcichthys alcicornis (Teleostei: Scorpaeniformes), with internal gametic association

Elkhorn sculpin, Alcichthys alcicornis, is a marine teleost with a unique reproductive mode called "internal gametic association," in which sperm introduced into the ovary by copulation enter the micropylar canal of ovulated eggs in the ovarian cavity, but actual sperm-egg fusion does not occur until the eggs have been released into sea water. It is also known that this fish is a multiple spawner, which spawns at intervals of a few days for one month, and the sperm introduced into the ovary at the beginning of the spawning season retain their fertilizability for the entire period. To clarify how the fertilizability of sperm is maintained internally, the ultrastructure of sperm, the morphological characteristics related to sperm storage in the ovary, and the characteristics of sperm motility were investigated. Mature sperm generally have the normal form of teleost sperm, devoid of acrosomal structures. However, it was found that the midpiece is comparatively elongated and has a compact aggregation of many small-size mitochondria. The intraovarian sperm remained floating in the ovarian fluid throughout the spawning season. The sperm showed high motility in isotonic and weak alkaline solution, containing sodium ions, which was similar to the ovarian fluid of this fish. Sperm continued to move in artificial ovarian fluid for 7-14 days. Considering these results together, it is thought that the intraovarian sperm move throughout the spawning season due to the plentiful energy generated by the many mitochondria.