Sex Differentiation and Pubertal Development of Gonads in the Viviparous Mosquitofish, Gambusia affinis

Abstract

The ontogenetic development of gonads from embryo to adult was observed histologically in the viviparous teleost, Gambusia affinis. Primordial germ cells (PGCs) appeared in the subendodermal space of the embryo 14 days before birth, and then transferred to the dorsal mesentery to form paired genital ridges 12 days before birth. The PGCs proliferated in the genital ridge, forming gonadal primordia 10 days before birth. All gonadal primordia differentiated to the ovary containing oocytes 2 days before birth, but then redifferentiated to the ovary and testis just after birth. This indicates that the mosquitofish is a juvenile hermaphroditic species. The characteristics of gonadal sex differentiation just after birth were enlargement of the oocytes in females, and invasion of somatic cells from the hilar region to an inner portion of the gonad in males. The paired ovary fused at the basal area 5 days after birth, then on the ventral and dorsal portions, developing into a single ovary 10 days after birth. During this time a single ovarian cavity was formed on the dorsal portion of the ovary. The paired testes fused only at the basal area and became a single testis having two main lobes 10 days after birth. The oocytes gradually developed and began vitellogenesis 100 days after birth, but did not reach maturation until 110 days after birth. Spermatogenic cells formed cysts at 20 days, began meiosis at 70 days, and matured to form sperm balls 90 days after birth. The male fish sexually matured earlier than the female.

Experimental Study on Diflubenzuron: Degradation in Freshwater and Bioconcentration in Mosquitofish Following Chronic Exposure

“…affinis remains one of the best candidates for biological control programs against mosquitoes [13,14]. This fish has been the subject of several studies including be- havioural ecology, histopathology, reproductive biology, endocrinology and toxicology [33][34][35]. The normal development of the ovaries has already been described [27,36] and the obtained data provide an experimental basis to study the activity of IGRs on females.…”

Gonadal morphogenesis and sex differentiation in intraovarian embryos of the viviparous fishZoarces viviparus (Teleostei, Perciformes, Zoarcidae): A histological and ultrastructural study

“…In other species, such as the perch (Lepori, 1980), the Atlantic halibut Hippogossus hippoglossus (Hendry et al, 2002), tilapia species Oreochromis (Nakamura and Takahashi, 1973;Nakamura et al, 1998), the common carp (Komen et al, 1992), and the goldfish, Carassius auratus (Nakamura, 1978) anatomical differentiation indicated by different types of ovarian cavity formation also precedes cytological differentiation of germ cells. However, in species such as the Japanese medaka (Satoh and Egami, 1972;Kanamori et al, 1985), the guppy, Poecilia reticulata (Miyamori, 1964), and the mosquitofish, Gambusia affinis (Koya et al, 2003) the opposite has been reported to occur. The process of primary oocyte growth (previtellogenesis) in the eelpout resembles that commonly described in teleost species (Bromage and Cumaranatunga, 1988;Tyler and Sumpter, 1996).…”

“…No cyst of proliferating spermatogonia or spermatocytes indicating spermatogenesis was present. In other species, spermatogenesis begins later than in females, such as 40 -50 dph in Japanese medaka (Kanamori et al, 1985;Hamaguchi, 1992), e.g., 50 -70 dph in tilapia (Nakamura and Takahashi, 1973;Nakamura and Nagahama, 1989;Nakamura et al, 1998), 70 dph in mosquitofish (Koya et al, 2003), 90 -120 dph in fathead minnow (van Aerle et al, 2004), and 120 dph in common carp (Komen et al, 1992).…”

“…In fathead minnow, the formation of the putative sperm ducts, blood vessels in the distal and proximal regions of the gonad, as well as the formation of testicular lobules are indicative of testicular differentiation at 25-60 dph (van Aerle et al, 2004). The initial formation of efferent ducts or of sperm ducts is one of the early signs of testicular differentiation in tilapia (Nakamura and Takahashi, 1973;Nakamura and Nagahama, 1989), guppy (Miyamori, 1964), mosquitofish at 20 dph (Koya et al, 2003), and Japanese medaka at 20 -40 dph (Kanamori et al, 1985). Similarly, initial formation of testicular lobules and the appearance of blood vessels located between the lobes indicate testicular differentiation in Japanese medaka at 10 dph (Kanamori et al, 1985;Hamaguchi, 1987Hamaguchi, , 1992, channel catfish, Ictalurus punctatus, at 85-95 dph (Patiñ o and Takashima, 1995;Patiñ o et al, 1996), and southern flounder, Paralichthys lethostigma (Luckenbach et al, 2003).…”

Sexual determination and differentiation in teleost fish

“…Gambusia affinis (Koya et al 2003), Cichlasoma dimerus (Meijide et al 2005), zebrafish (von , Zoarces viviparus (Rasmussen et al 2006), rainbow trout (Vizziano et al 2007), the Adriatic sturgeon Acipenser naccarii (Grandi and Chicca 2008), and Gasterostus aculeatus (Lewis et al 2008).…”