西伯利亚鲟仔鱼侧线系统的发育

Development of the lateral line system in juvenile Siberian sturgeon(Acipenser baerii)

鲟鱼属软骨硬鳞鱼,在电感受器的进化中占据着极为重要的地位。该文以光镜和扫描电镜手段研究了西伯利亚鲟侧线系统早期发育,包括侧线基板发育及感觉嵴的形成、侧线感受器的发育和侧线管道的形成。1日龄,听囊前后外胚层增厚区域出现6对侧线基板;除后侧线基板细胞向躯干侧面迁移外,其他侧线基板均形成感觉嵴结构;每一侧线基板中均有神经丘原基形成。7日龄,壶腹器官在吻部腹面两侧出现,壶腹器官的发育比神经丘晚一周左右。9日龄,神经丘下的表皮略有凹陷,侧线管道开始形成。29日龄,在吻部腹面两侧可见少数个别的壶腹器官表皮细胞覆盖壶腹器官中央区域留下3～4个小的开口;壶腹管内可见大量的微绒毛存在,在其他鲟形目鱼类、软骨鱼类中也存在类似的结构。57日龄,躯干侧线管道已完全埋于侧骨板中;壶腹器官主要分布在吻部腹面,3～4个聚集在一起,呈"梅花状",分布紧密,并且该部分皮肤表面凹陷,形成花朵状凹穴;侧线系统发育完善。

The Siberian sturgeon （Acipenser baerii Brandt）, a chondrostean, occupies an important position in the evolution of the electroreceptor. In order to more fully understanding the evolution of these receptors, we examined the development of the lateral line system during early ontogeny of the Siberian sturgeon by using light and scanning electron microscopes. We detected four major events in this process： the lateral line placodal development, the sensory ridge formation, the receptor formation and the canal formation. On day 1 of post hatching, all six lateral line placodes are present and the posterior lateral line placode starts actively migrating posteriorly along the mid-line of the trunk, depositing neuromasts at intervals on the way of migration. The other lateral line placodes elongate to form sensory ridges according to its destination line pattern over the head, all containing primordial neuromasts. By day 7, ampullary organs rise from the lateral zones of the ventral of the head, though this may lag up to one week behind of that of the neuromasts. On day 9, the epidermis under the neuromast slowly invaginates, and the bony lateral line canals begin to form. Towards day 29, the epidermal cells surrounded some single openings of the ampullary organs at the ventral surface of the head, begin to migrate, and then transform into 3 to 4 aggregate openings. By this point, abundant microvilli are visible on the surface of the receptor epithelium, similar to the structure in elasmobranches and other sturgeons. On the day 57 of post hatching, the trunk canal is fully embedded into the lateral scutes. By then, the majority of ampullary organs are highly concentrated on the ventral rostrum, arranged in clusters of 3？4, distributing closely such as the shape of quincunx, thus completing the formation of the lateral line system.