罗氏沼虾胚胎附着机制的初步研究

甲壳动物十足目的大多数种类,其受精卵自产出后就附着于亲体腹部,并完成胚胎发育过程直至孵化,这对于胚胎的发育、保护和幼体散布有重要的生物学意义。胚胎的附着机制较为复杂,与刚毛、卵柄、卵索、卵膜和黏液腺有关:卵柄和卵索的形成决定了胚胎发育的顺利进行;卵膜的变化影响着胚胎的附着;黏液腺在胚胎附着过程中形成卵柄和外层卵膜,胚胎是依靠卵柄或卵索附着于腹肢的刚毛上,进而完成胚胎发育过程。本研究采用常规组织学和扫描电镜的方法研究了罗氏沼虾(Macrobrachium rosenbergii)胚胎及其附着结构。结果表明,胚胎附着与母体腹肢的结构、黏液腺分泌的黏液相关,也与胚胎表面结构、次级卵膜的形态和结构密切相关。原肢底节和内肢刚毛密而长,基部有细小的分支,有利于胚胎的附着,外肢刚毛羽状则有利于胚胎的托附和保护。抱卵雌虾腹肢的原肢和内肢上布满腹肢黏液腺分泌的黏液;携卵刚毛中空、壁厚,刚毛外壁由微绒毛状结构组成,扩大了携卵刚毛的表面积,以利胚胎附着。胚胎外表面由初级卵膜和次级卵膜组成,次级卵膜主要由卵巢黏液腺分泌的黏液参与形成。排卵时,受精卵依靠坚韧的次级卵膜相互粘连,同时,部分受精卵在刚毛上滑动、旋转,并借助次级卵膜逐渐形成了卵柄或卵索固着在腹肢刚毛上。从受精卵到胚胎孵化,胚胎之间最主要的连接方式是依靠次级卵膜的连接。胚胎的表面有许多褶皱和黏液,利于胚胎的附着以及胚胎对溶氧和小分子物质等的通透。以上结构与附着相适应,保证了胚胎发育的顺利进行和幼体的正常孵化。本研究旨为进一步认识甲壳动物胚胎附着机制、胚胎发育和人工育苗的研究提供参考。中国水产科学,2007,14(1):67-73]

Mechanism of embryo attachment in freshwater prawn, Macrobrachium rosenbergii

Fertilized eggs of most decapods in crustacean attach to female abdomen and finish their embryonic development.Embryo attachment has important biological significance in embryo protecting and scattering of larvae.The mechanism of egg-attachment is complex.People realized that embryo attachment has relevance to seta,egg stalk,egg funiculus,egg membrane and also mucus gland.Embryonic development depends on the formation of egg stalk and egg funiculus.Embryo attachment was affected by the differentiation of egg membrane.Egg stalk and outer egg membrane were formed from mucus during development.Embryos attached to female pleopods by peculiar structure,such as egg stalk,egg funiculus.In the present study,the structural features of embryo attachment systems of the freshwater prawn,Macrobrachium rosenbergii were investigated by scanning electron microscopy and histological methods.The results showed that embryo attachment have relevance to not only structure of pleopods,mucus that mucus gland excretive,but also characteristics embryo surface,morphology and structure of the secondary membrane.Embryos adhered to the setae of pleopodal basipodite and endopodite for hatching followed by spawning but no embryo attached on the setae of exopodite.The setae of pleopodal basipodite and endopodite were smooth for embryo attachment while the setae of exopodite were branched and suitable for collecting and protecting embryo.Lots of mucus secreted by pleopod mucus gland was distributed on pleopodal basipodite and endopodite.Ovigerous setae were hollow and thick.The surface of setae was full of microvillus.These structures enlarged the surface of setae,which benefited to attachment of embryos.The surface of embryos was composed of primary egg membrane and secondary egg membrane.The secondary egg membrane was formed mainly by mucus which from ovary mucus gland.When eggs were discharged,fertilized eggs were connected to each other by means of the secondary membrane.Egg stalk and funiculus were formed gradually from the secondary membrane when fertilized eggs gliding and rotating on the setae.From fertilized egg stage to late embryonic development stage,the main connection between embryos was the secondary membrane.A lot of wrinkles and mucus were found on the surface of embryos.These structures not only benefit the attachment for embryos,but also benefit the absorbing of oxygen and the passage for some substance.The characteristics of these embryo attachments ensure embryonic development and hatching successfully.The results obtained in the present study help know better on mechanism of egg-attachment,embryonic development and larva culture of Macrobrachium rosenbergii,and also other species of crustacean.Journal of Fishery Sciences of China,2007,14(1):67-73]