日本七鳃鳗胚胎发育及卵黄囊期仔鱼的异速生长

EMBRYOLOGICAL STAGES AND ALLOMETRIC GROWTH DURING YOLK-SAC LARVAE OF LAMPETRA JAPONICA (MARTENS)

  • 摘要: 通过观察日本七鳃鳗Lampetra japonica (Martens, 1868)胚胎外部形态和内部组织结构变化, 描述受精卵从卵裂至器官形成以及仔鱼孵出的发育阶段, 采用实验生态学方法研究卵黄囊期仔鱼的异速生长模式。结果表明: 日本七鳃鳗卵子为乳白色, 呈卵圆形; 受精卵卵裂方式为全卵裂; 胚胎发育过程主要包括卵裂期、囊胚期、原肠胚期、神经胚期、头凸期、孵出前期和孵出期, 历时11—12d; 初孵仔鱼为乳白色, 全长约(3.41±0.24) mm, 体质量约为0.0006 g。日本七鳃鳗胚胎发育研究可为了解七鳃鳗胚胎发育过程, 早期脊椎动物的起源和发育进化研究提供参考。卵黄囊期内仔鱼身体各部分中, 头长和尾长均表现出快速生长, 同在7 日龄出现生长拐点, 且生长拐点后的生长速率都大于生长拐点前的生长速率; 而仔鱼体长在卵黄囊期内表现出慢速生长。在头部器官中, 吻长、鳃前长和鳃长均表现出快速生长现象, 吻长和鳃长分别在9日龄和8日龄出现生长拐点; 口笠长在3日龄时出现生长拐点, 在生长拐点前为等速生长, 而在生长拐点后表现出快速生长; 眼径和眼鳃间距则分别表现出等速生长和慢速生长。泄殖孔在卵黄囊期内未出现生长拐点, 生长速率相对于全长生长速率表现出快速生长现象。七鳃鳗卵黄囊期仔鱼的异速生长是在长期进化过程中, 适应早期生活环境和独特的生活方式而形成特有的发育机制。

     

    Abstract: Early embryology of the Lampetra japonica has been studied based largely on external morphology and histology. In current study, ecological experiment was conducted to investigate the allometric growth of L. japonica yolk-sac larvae. The results indicated the ovulated egg was creamy-white with the oval shape. The cleavage of zygote was holoblastic cleavage. The early embryology of L. japonica had been characterized into cleavage, blastula, gastrula, neural plate and groove, head, prehatching and hatching. The embryo breaks through the fertilization membrane at 11—12 day-post-fertilization. Newly-hatched larvae were (3.41±0.24) mm in total length and about 0.0006 g in weight. Study of the early embryology ofL. japonica may provide the basis for understanding the origin and evolution development of vertebrates. During yolk-sac stage, head and tail length exhibited positive allometric growth, and trunk exhibited negative allometric growth. The inflection point was at 7 day-post-fertilization for both head and tail length. The head and tail length exhibited positive allometric growth before and after the growth inflection point and the growth was higher post the inflection point. In terms of the dimensions of organs in head, snout length, prebranchial length and branchial length exhibited positive allometric growth. The inflection point appeared at 9 day-post-hatch for snout length and at 8 day-post-hatch for branchial length, respectively. The inflection point of disc length occurred at 3 day-post-hatch, and the disc length exhibited isometric allometric growth to the inflection point, then became positive allometric growth. The eye length was characterized by isometric allometric growth and had no inflection point. The postocular length exhibited negative allometric growth. The cloacal slit length exhibited positive allometric increase and hads no inflection point. The allometric growth pattern of L. japonica yolk-sac larvae enabled rapid development of the organisms which has important function to adapt to the early life stage and increases their survival rate.

     

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