Spermatogenesis And Fertilization Process Of Cynoglossus Semilaevis Günther

In this paper, gonadal sex differentiation, structure of testis, spermatogenesis, and spermatozoa of Cynoglossus Semilaevis Günther, and fertilization process of C. Semilaevis Günther and Scophthalmus maximus was studied by means of histological staining mehods and electron microscopy.In yolk sac stage, primordial germ cells (PGCs) was located between gut and mesonephric ducts; PGCs was migrating towards gentital ridge in larva 5 days after hatching(DAH); in larva 10 DAH, PGCs arrived at germinal ridge and began to form primordial gonad together; in larva 15~26 DAH, primordial gonad begin to prolongate; in larva 36 DAH, with mitotic multiplication, primordial gonad elongated ventrally, stretching from the ventral end of kidney to the posterior end of abdominal cavity, and had an abundance of connective tissue. After a long period of undifferentiation stage, some of the primordial gonad began to mitotic multiplication and appeared clusters of oogonia in 62 DAH which indicated the ovarian differentiation of semi-tongue sole. Presumptive ovarian cavity began to form at 100 DAH. Ovarian cavity was formed entirely in 190 DAH. Testicular differentiation of semi-tongue sole is posterior to ovarian differentiation. At 80DAH, presumptive testis began to enlarge through mitotic multiplication. Formation of efferent duct and blood vessels occured in 100 DAH, which was anatomical features of testicular differentiation. At 150 DAH, testis began to develop spermatogonial clusters of cysts and form seminal lobule, which was cytological features of testicular differentiation. By 190 DAH, testis developed into maturation stage.Testes of Cynoglossus semilaevis was lobular type, consisted of seminiferous lobular, interlobular septum and spermaduct. Seminiferous lobular consisted of various stages of spermatogenic cells and Sertoli cells. Spermatogenic cells consisted of primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes and spermatids. Within a spermatogenic cyst, all the spermatogenic cells were at the same developmental stage. Characters of spermatogenic cell in each stage were discribed in detail. Spermiogenesis included formation of a flagellum, condensation of nucleus that will form sperm head, development of middle piece, discarding of residual cytoplasm, formation of sleeve which contained some mitochondria, etc. Mature sperms were released from cysts and transferred into lobular lumen.Spermatozoon of C. semilaevis consisted of three parts: head, midpiece, and tail. Spermatozoon had no acrosome, nucleus of sperm was horse-hoof shaped. Nuclear fossa was deep, and at bottom of it lacated centriolar complex which consisted of proximal centriole and basal body. Five to six mitochondria localized behind nucleus in a circle, forming midpiece of the sperm. Length of tail was about 43±2.4μm (n=5). Structure of axoneme was typical"9+2"pattern. Lateral fins and sacciform structures were found at some parts of tail. Structural characteristics revealed that the sperm of C. semilaevis belonged to primitive type in teleostean fish.Morphology of surface structure and chorion of eggs, site and structure of micropyle, and early process of sperm penetration were studied by electron microscopy. Speed of sperm penetration was vary fast, 2 seconds post insemination, there had been sperm entried egg. Changes of some structure occured during sperm penetration, for the jagged circle in inner wall of the micropyle tunnel turned into slippery circle. Tissue section of fertilized eggs showed that after sperm entering into egg, male pronucleus and female pronucleus was formed one after another. They contacted with each other and formed nucleus of zygote. It could be sure that the pattern of fertiliztion of C. semilaevis is monospermy.Egg and sperm shapes, process of sperm penetration, and structure changes of fertilized egg of Scophthalmus maximus L. were examined by eletron microscopy. And observation results of tissure section showed that mature eggs of S. maximus L. remained at metaphase of second maturation division. The egg was activated as sperm penetrating into the egg, with development of second maturation division and cortex reaction. At 15 minutes after insemination, sperm-aster appeared. At 20minutes after insemination, male pronucleus was formed prior the formation of female pronucleus, and later they got closer to each other. At 30 minutes after insemination, male and female pronuclei combined together and a clear junction line was observed. At 40 minutes after insemination, zygote nucleus formed and later karyotheca became faint. At 50 minutes after insemination, zygote nucleus developed into metaphase of the fist mitosis, and then at 60 minutes, first karyokinetic division was finished. From the results, it was concluded that fertilization type of turbot was monospermism and combine type of male and female pronuclei was conjugation.