Gametogenesis And Reproductive Characteristics Of Sea Cucumber Holothuria Scabra In Hainan Island

The gametogenesis and reproductive characteristics of sea cucumber Holothuria scabra by light microscope and ultrastructure. The gonadal development and reproduction cycle of H. scabra in Hainan Island were studied by paraffin section technique and H.E (haemotoxylin and eosin) staining method. This study revealed the elementary characteristics on Spermatgenesis and reproduction cycle of H. scabra, and would provide important guidance for its wild population protection and artificial breeding in future. The main content is composed of 3 parts as follows.1. Spermatogenesis and Sperm Morphology of Sea Cucumber H. scabraThe spermatogenesis was shown to be divided into five stages: spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid and spermatozoon. The differentiation of spermatids was subdivided into three stages, the early spermatid:formation of proacrosomal vesicle at the front of the nucleus; the mid-spermatid: periacrosomal material in the cavity of acrosome; the later spermatid:the cytoplasm shrinking backward and becoming a flagellum, until the formation of central section of the spermatozoon. The mature spermatozoon as a flagellated a type is about 60 ?m long, and consists of three parts:head, middle piece and tail. The head is spherical in shape with an apical acrosome which has about 1.8 ?m of vertical axis and about 1.4 ?m of horizontal length The acrosome is an U-shaped cystid, and the periacrosomal material space is crescent in shape; the chromatin in the acrosome is condensed into the nucleus. A large mitochondria and centriole complex are in the mid-piece of the spermatozoon, and in the tail, the flagellum is composed of typical "9+2" microtubular structure.2. Ultrastructure of oogenesis and vitellogenesis of Sea Cucumber H. ScabraOocyte of H. scabra belongs to isolecithal egg and its oogenesis inc-ludes following three stages:oogonium, pre-vitellogenic oocyte, Vitellog-enic oocyte, while the stage of vitellogenic oocyte includes early vitellog-enic oocyte, mid-vitellogenic oocyte and late-vitellogenic oocyte. Besides a large and oval nucleus, oogonium contains fewer mitochondrias in this stage. The nuclear of pre-vitellogenic oocyte contains a vacuolated nucle-oli, also known as a germinal vesicle; At the early stage of vitellogenesis, various well-developed organelles emerg in cytoplasm; At the stage of the mid-vitellogenic oocyte, active endogenous yolk formation greatly occurs and many kinds of organelles directly participate in this process, At the stage of late-vitellogenic oocyte, the oocytes are the biggest and contain fewer numbers of organelles, the germinal vesicle of eccentric position is near the basal protuberance. Golgi apparatus, mitochondrias and ribsome are the dominant organelles which take part in the formation of endogen-ous yolk, while active microphagocytosis of plasma membrane play the main role to form exogenous yolk.3. The gonadal development and reproductive characteristics of H. scabra in Hainan IslandThe gonadal development of H. scabra in Hainan Island can be divided into five stages as follows:recovery (stage ?), growing (stage ?), mature (stage ?), partly spawned (stage ?) and spent (stage ?). (1) Testis development at different stages:stage ?:germ tube wall was the thickest; stage ?:germinal epithelium became thinner and the longitudinal folds extended into the lumen; stage ?:lumens were packed densely with spermatozoas; stage ?:germinal epithelium was recovered into the original folding morphology; stage ?:few of relic spermatozoa were remained in the lumen. (2) Ovary development at different stages: stage ?:oogonias and previtellogenic oocytes were growing along the germinal epithelium; stage ?:central lumen contained many vitellogenic oocytes, which were growing around oogonias and previtellogenic oocytes; stage ?:lumen was packed densely with vitellogenic oocytes; stage ?:number of vitellogenic oocytes reduced and some previtellogenic oocytes reappeared on the germinal epithelium, meanwhile some nutritional phagocytes began to occur in the lumen; stage ?:few of relic vitellogenic oocytes were remained in the lumen. Annual change analysis of gonad development indicated that H. scabra from Xincun Bay, had a synchronous pattern of gonad development between males and females, and spawned in batches; the wide population had a continuous spawning period throughout the whole year during which two main spawning peaks occurred respectively from May to August (in summer) and from December to February (in winter).