Histological Studies On The Origin And Migration Of The Primordial Germ Cells And Gonalal Sex Differentiation In Large Yellow Croaker Larmichthys Crocea

In this paper, the origin and migration of the primordial germ cells (PGCs), the formation ofthe primordial gonads, the process of gonadal sex differentiation and development and itsrelationship to body length (BL) in the large yellow croaker Larimichthys crocea were studiedwith histological methods.The results were as follows:(1) The sampled fertilized eggs of large yellow croaker hatched on Oct.1in2010at26℃.The temperature for nursery was25.0-26.0℃. The PGCs of large yellow croaker first appearedin early gastrula in the embryo8h after fertilization, situated in the inside mesoderm ofembryonic shield. At the age of8days post hatch (dph), when larvae gained5.70mm-6.15mmin body length (BL), genital ridge formed. In larvae of16dph (BL17.6mm-19.2mm),primordial germ cells had migrated into genital ridge and primordial gonad formed.(2) In fries of20dph (BL17.6mm-19.2mm), a pair of primordial gonads present in theabdominal cavity. Ovarian differentiation occurred at55dph (BL27.5mm-37.0mm), and wascharacterized by the presence of clusters of oogonia. The formation of ovarian cavity andmeiosis of germ cells began simultaneously at the age of60dph (BL28.0mm-37.2mm). Thepresence of primary oocytes occurred at the age of120dph (BL39.2mm-51.0mm). Thedifferentiation of testis began at the age of95dph （BL38.0mm-48.0mm）and wascharacterized by the presence of efferent duct and the scattering of somatic cells throughout thegonad. Cyst of spermatocytes could be seen at215dph (BL44.0mm-59.2mm) and testislobules started to form at230dph (BL56.2mm-72.8mm). These results suggested that largeyellow croaker is a differentiated gonochorist, and differentiation of the ovary occurs earlier inthat of testis.(3) Fries of large yellow croaker of the autumn batch of fish were sampled and divided into5groups according to body length. The development of gonads was consistent with the growthof body length since the gonads of larger fries developed faster than that of of smaller ones in thesame batch. Therefore, we concluded that gonadal differentiation of large yellow croakerappeared to be related to body length more than to age.