Kawaguchi Mari, Sano Kaori, Yoshizaki Norio, Shimizu Daisuke, Fujinami Yuichiro, Noda Tsutomu, Yasumasu Shigeki
1 Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan.
Zoolog Sci. 2014 Nov;31(11):709-15. doi: 10.2108/zs140018.
We compared several characteristics of the pelagic eggs of Verasper variegatus with those of demersal eggs of Pseudopleuronectes yokohamae, both in the order Pleuronectiformes (halibuts or flatfishes). V. variegatus eggs had about twice the diameter of P. yokohamae eggs. However, the total egg protein weight of P. yokohamae was similar to that of V. variegatus. The specific gravity of P. yokohamae eggs was calculated to be 7-fold that of V. variegatus. The difference in size is the main feature distinguishing the two types of egg. The thickness of the egg envelope of P. yokohamae- more than twice that of V. variegatus-must affect the manner of hatching. The amount of hatching enzyme synthesized in pre-hatching embryo was estimated to be larger in P. yokohamae than V. variegatus. The distribution of hatching gland cells differed between the species. In V. variegates embryos, these were located on the yolk sac as a narrow ring-shaped belt, resulting in cleavage of the egg envelope into two parts by digesting a limited region of the egg envelope, called "rim-hatching". The hatching gland cells of P. yokohamae embryos were distributed all over the surface of the yolk sac, forming a hole through which the embryo could escape. Thus, the location of the hatching gland cells in pre-hatching embryos varied during the evolution of the Pleuronectiformes, depending on the egg type and manner of hatching.
我们比较了条斑星鲽浮性卵与横滨黄盖鲽沉性卵的几个特征，二者均属于鲽形目（比目鱼或扁鱼）。条斑星鲽的卵直径约为横滨黄盖鲽卵的两倍。然而，横滨黄盖鲽卵的总蛋白重量与条斑星鲽的相似。据计算，横滨黄盖鲽卵的比重是条斑星鲽卵的7倍。大小差异是区分这两种卵的主要特征。横滨黄盖鲽卵膜的厚度——超过条斑星鲽卵膜厚度的两倍——必定会影响孵化方式。据估计，横滨黄盖鲽孵化前胚胎中合成的孵化酶量比条斑星鲽的大。孵化腺细胞的分布在这两个物种之间有所不同。在条斑星鲽胚胎中，这些细胞位于卵黄囊上，呈狭窄的环形带，通过消化卵膜的有限区域，使卵膜分裂成两部分，即“边缘孵化”。横滨黄盖鲽胚胎的孵化腺细胞分布在卵黄囊的整个表面，形成一个胚胎可以从中逃脱的孔。因此，在鲽形目的进化过程中，孵化前胚胎中孵化腺细胞的位置因卵的类型和孵化方式而异。
