狭鳕早期胚胎发育的形态结构观察

利用显微数码摄像系统,活体观测、拍摄了狭鳕受精卵的早期胚胎发育过程,详细描述记录不同发育时相胚胎的形态特征、发育时间等。选取6个发育期(未受精、细胞分裂期、囊胚期、原肠胚期、胚体发育期、将孵化前期)的照片,利用Image J软件测量不同发育期的卵径,以探讨狭鳕早期胚胎发育过程中卵径的变化。此外,利用扫描电镜观察了4个胚胎发育期(未受精期、2细胞期、原口关闭期、孵化前期)受精孔及卵膜的形态结构。结果表明,狭鳕产浮性分离卵子,卵膜单层、透明光滑,卵黄均匀,无油球,卵径1.45~1.58 mm。在水温(6.3±1.24) ℃,盐度34时受精后约1 h胚胎形成,24 h后进入囊胚期,61 h后进入原肠胚期,134 h后进入器官形成早期,161 h后心脏开始跳动,319 h后开始孵化。在整个胚胎发育过程中,狭鳕卵子的直径呈现逐渐增大的趋势。亚显微观察显示,狭鳕受精孔为Ⅱ型,受精孔前庭平坦,但受精孔孔道较长。未受精时,受精孔开放,卵膜上多皱褶,卵膜壁孔不明显;2细胞期时,受精孔被卵周液分泌物阻塞,卵膜皱褶减少,卵膜壁孔明显;原口关闭期时,受精孔呈半开放状态,卵膜褶皱增多,卵膜壁孔不明显;即将孵化期时,受精孔完全塌陷,卵膜表面十分粗糙,卵膜壁孔明显。由此可见,狭鳕卵子卵径、受精孔和卵膜结构的动态变化都与整个胚胎发育过程紧密相关,其对提高卵子受精率、卵子在海底正常发育和散布,卵子发育过程中防止多精受精和细菌感染具有重要意义。

Observation on morphological structure of the early development of Theragra chalcogramma

The embryonic development pattern of walleye pollock and the morphological characteristics of fertilized eggs were observed and recorded from October to December in 2008.The egg diameters in six stages were measured and the egg envelopes of seven stages were also studied with scanning electron microscopy.The egg of walleye pollock was pelagic,without oil globules.The diameter was 1.45-1.58 mm,the incubated temperature was(6.3±1.24) ℃ and the salinity was 34 psu.The microscopic observation showed the fertilization tube opened with(4.33±0.31) μm pore diameter;the pore canals of the egg envelope were inconspicuous;the interval of micropyle and density of the pore canals of the egg envelope were(1.46±0.31) μm and 21.1-30.6/100 μm2 respectively.The micropyle with the micropyle canal was completely plugged with material at the 2-cell stage,and the fertilization pore diameter was(5.26±0.29) μm.The egg envelope contained less ruffles and the pore canals of the egg envelope became more prominent and the interval of micropyle was(2.04±0.35) μm.The density of the pore canals of the egg envelope was 14.7-20.3/100 μm2.After the closing phase of blastopore,the fertilization pore of egg presented the open state;few secretions were adhered to its periphery region.The diameter of the fertilization pore,interval of the pore canals and density of the pore canals of the egg envelope were(4.48±0.15) μm;(1.70±0.23) μm;and 23.59-27.53/100 μm2,respectively.Approaching the incubation period,the egg envelope had a rough surface,on which the pore canals were inconspicuous with a(2.56±0.22) μm interval and the density was 12.38-15.97/100 μm2.The diameter of egg,the fertilization pore,as well as the dynamic change of structure of egg envelope,were closely related to the embryonic development of Alaska pollock.The above indexes had great importance in improving the fertility rate of egg,facilitating the normal development and spread of egg on seabed,and preventing both polyspermy and bacterial infection during the egg development process.