Histological observation on gonadal sex differentiation in large large yellow croaker ( Larimichthys crocea)

The process of gonadal development and differentiation of large yellow croaker Larimichthys crocea was investigated with histological methods. The sampled fries were hatched on Sept. 22nd , 2009 at 26℃. The temperature for nursery and culture were 22.0 ℃ - 25.8 ℃ and 11.5 ℃ - 25.6 ℃, resepectively. At the age of 20 days post hatch (dph ), when the fries gained 17.6 mm - 19.2 mm in body length (BL), a pair of primordial gonads were present in the abdominal cavity. Ovarian differentiation occurred at 55 dph (BL 27.5 mm - 37.0 mm), and was characterized by the presence of clusters of oogonia. The formation of ovarian cavity and meiosis of germ cells began simultaneously at the age of 60dph (BL 28.0 mm - 37.2 mm). The presence of primary oocytes occurred at the age of 120 dph (BL 39.2 mm - 51.0 mm). The differentiation of testis began at the age of 95 dph (BL 38.0 mm - 48.0 mm) and was characterized by the presence of efferent duct and the scattering of somatic cells throughout the gonad. Cyst of spermatocytes could be seen at 215 dph (BL 44.0 mm - 59.2 mm) and testis lobules started to form at 230 dph (BL 56.2 mm -72.8 mm). These results suggested that large yellow croaker is a differentiated gonochorist, and differentiation of the ovary occurs earlier than that of testis.