Studies On Reproductive Biology And Spermigenesis In Cultured Sepiella Maindroni

Sepiella maindroni belonging to the class Mollusca,Cephalopoda, Dibranchia,Decapodiformes,Sepioidea,Sepiidae,Sepiella,is widely spreading in coastal areas,especially in the north of East China Sea in Zhejiang.It is a traditional species of fishery with high economical value. The gonad development and reproductive character of natural groups of Sepiella maindroni have been studied at home and abroad.In artificial conditions,reproductive character of Sepiella maindroni has changed dramatically.Natural groups of Sepiella rnaindroni only breed once a year,while cultured Sepiella maindroni can breed twice a year.In the present study,the reproductive biology in cultured Sepiella maindroni was investigated for the first time,and transmission electron microscopy was used to study the ultrastructure of spermiogenesis of Sepiella maindroni,and the morphological structure of spermatozoa that is one of the important characters of reproductive evolution was discussed.The histological structure of reproductive system and gonadic development were studied as well.Through this research,we not only accumulate the base date on artificial grow seeding and exploit utilization of Sepiella maindroni,but also fill up the blank on ultrastructure of mature sperm of Cephalopoda,Decapodiforrnes at home.The main result are as follow:1 The study of reprocuctive biologyIn artificial conditions,Sepiella maindroni can breed twice a year. It’s fecundity is proportional to body length,body weight,and Nidamental gland weight.Absolute fecundity is also proportional to body length and body weight.2 The histological study of male reprocuctive systemHistological observation and light and electron microscope revealed that the male reproductive system in Sepiella maindroni consists of spermary and genital duct.The genital duct includes vas deferens, vesicula seminalis,prostate gland,spermatophore and penis.Spermary consists of numerous spermaductus.There are germ cells which are immovable in the spermaductus.Muture spermatozoa live in the middle of tubule arranging regularly to one same direction.Spermatozoa modality is slightly curved long cylindrical spindle.3 SpermigenesisSpermiogenesis of Sepiella maindroni was investigated by transmission electron microscope.Early spermatid of Sepiella maindroni exhibits an ovoid nuclear with dense irregular patches.Mitochondrias, Golgi bodies and one triplet substructure centrioles spread around the cytoplasm.Subsequently,the following morphological changes take place:(1) The chromatin in spermatid undergoes a process of granulation, fine fibrosis,and thick fibrosis,and finally is highly condensed with high electron density.(2) The morphology of the nuclear changes gradually from ovoid or ellipse,and long ellipse to long cylindrical spindle-shaped, posterior nuclearfossa is formed by the concave of the posterior nucleus at lateral.And then the"9+2"arrangements of axoneme extended from centriole are formed.(3) Golgi saclikes accumulate density materials and fuse into acrosoml vesicle,and finally the pre-acrosome becomes an inverted U-shaped acrosome.(4) Mitochondrias migrate posteriorly to the nuclear and form mitochondria spur at mid-piece of tail.4 Ultrastructure of mature spermThe ultrastructure of the spermatozoon of Sepiella maindroni was investigated using a transmission electron microscope.It is showed that each spermatozoon consists of two parts,the head and the tail.The tail can be divided into a middle piece,a principal piece and an end piece.The head is composed of an inverted U-shaped acrosome and an elongated nucleus.The acrosome filled with materials of a high electron density is positioned in the nucleus apex.Nucleus is slightly curved long cylindrical spindle-shaped,and is highly condensed chromatin with high electron density.Mitochondria spur is composed of numerous mitochondrias surrounds flagellum in middle piece.The flagellum is composed of a "9+2" axoneme surrounded by nine bundles coarse fibres and forms the "9+9+2" arrangement.In principal piece,mitochondria spur disappears and dense coarse granules surround axoneme.The end piece is thin and long and consists of an axoneme and a plasma membrane.Subsequently coarse fibres of the flagellum gradually decrease in diameter and are eventually lost.