ABSTRACT
The female genital system consists of the ovaries and in most species a duct system communicating with the exterior. Fish ovaries may be of three types: cystovarian, gymnovarian, or secondary gymnovarian. Oogenesis involved the proliferation of oogonia by mitosis and the development of oocytes. Six stages are demonstrated: oogonia, early oocyte, late oocyte, vaculated follicles, yolk globule stage (vitellogenesis), and mature follicles. The follicular atresia is a common phenomenon of the teleost ovary and includes both oocytes and their follicular wall. Various types of cells were detected in the stroma, include telocytes, rodlet cells, mast cells, eosinophils, neutrophils, lymphocytes, fibroblasts, macrophages, melanocytes, adipocytes, dendritic cells, and endocrine (steroidogenic, interstitial) cells. Testis of teleosts is of two types: lobular and tubular. In the lobular type, a system of seminiferous tubules (STs) is arranged radially from the dorsal and lateral wall of the testis to the central lumen. The central lumen leads to efferent ducts (EDs), which are connected with each other to open into the sperm duct or vas deferens that leads to the urogenital pore. The testicular parenchyma consisted of branching tubular STs and interstitial tissue. The STs are made up of spermatocysts, where spermatogenesis occurred. In the tubular testis type, the sperms present only at the apex of the tubule, and cysts are migrating to the ED.
Ovaries and testes develop from paired masses of mesodermal tissue on either side of the dorsal mesentery in the dorsolateral lining of the peritoneal cavity. These indifferent genital ridges bulge into the developing coelom and are later invaded by primordial germ cells that will eventually give rise to oogonia or spermatogonia (SG). Covering the surface of the ovary is the so-called germinal epithelium (GE), which is continuous with the peritoneum lining the coelom.
Reproduction in most fishes is cyclic; although, the length of the cycle is extremely variable, which is correlated with photoperiod and temperature 270variations. Certain salmonid and eel species spawn only once and then die, others may breed every 2 or 3 years, but most breed once or several times a year. Some teleosts and some species of oviparous skates appear to breed throughout the year.
Fishes that spawn once then die have synchronous ovaries in which all oocytes are at the same stage of development. Species that spawn once per year during short breeding season display group-synchronous ovaries which at least two populations of oocytes at different developmental stages are present; this type is common in teleosts. Ovulation at group-synchronous ovaries may occur at intervals over the breeding season so that the oocytes are released in batches. An asynchronous ovary contains oocytes at all stages of development and occurs in species that spawn many times during a long breeding season as goldfish, Carassius auratus.
The genital papilla is a small and fleshy tube located behind the anus that can determine the sex of the fish as this papilla is relatively smaller in females than those of males. In addition, females had three openings: the anus, the oviduct (OD) in which the eggs exit, and the urinary pore. Both the OD and the urinary pores are found in the genital papilla.
The female genital system consists of the ovaries and in most species a duct system communicating with the exterior. In addition to its cytocrine function in producing fertilizable gametes, the ovary shares with the testis the complementary endocrine function of secreting a variety of steroid hormones that regulate the development of the germ cells. ODs may be simple passageways for the eggs but often their lining is glandular and forms protective coverings for the eggs.
