多斑岭鳅嗅觉器官表面超微结构及其形态适应

Surface Ultrastructure of the Olfactory Epithelium and Morphological Adaptation of a Cave-dwelling Loach, Oreonectes polystigmus

多斑岭鳅（Oreonectes polystigmus）是营洞穴生活的鱼类,嗅觉器官在其生活中发挥了重要作用。本文对保藏于中国科学院动物研究所鱼类标本馆的4尾多斑岭鳅标本进行解剖,利用扫描电镜观察多斑岭鳅嗅囊上皮超微结构,以期了解嗅觉器官适应洞穴黑暗环境而产生的形态适应。多斑岭鳅的嗅囊呈椭圆型,嗅囊长径平均为2.27 mm,嗅囊长径与眼径比平均为1.36,揭示其为＂嗅觉＂鱼类。其嗅轴为直线型,嗅囊腔内对称紧密排列2排嗅板,嗅板数为22~24个。单个嗅板呈卜状亚型,舌状突起较发达。观察发现,非感觉纤毛连续广布在嗅板各个部位,但在嗅板近嗅轴处较少,此处裸露的表皮多褶皱,其上分布很多细微小孔。感觉纤毛主要分布于非感觉纤毛分布较稀疏的地方。上皮表面微绒毛多,一般在非感觉纤毛下,前后两端嗅板上的微绒毛数量相对较少。多斑岭鳅嗅囊水动力机制应属嗅上皮纤毛运动机制。嗅孔分布不均,中间嗅板上的嗅孔较嗅轴前、后分布的嗅板为多,同一嗅板上近嗅轴处的嗅孔最多。由于纤毛分布不均,嗅上皮可分为裸露区和非裸露区,一般裸露区和非裸露区边界清晰,嗅轴上非感觉纤毛和微绒毛主要分布在非裸露区的凹槽里。嗅轴和嗅板近嗅轴处裸露区面积较大,嗅轴裸露区上皮被一系列的连续的微脊切割成多边形,多边形内具有许多隆起与小孔。嗅轴处正是嗅囊中水流回流的区域,为感受水中气味的重要位置,推测与洞穴生活的习性有密切关系。多斑岭鳅嗅囊形态属于G型,这类鱼类其嗅觉功能在鱼类生命活动中发挥了重要作用。同近缘的地表种相比,多斑岭鳅具有较多的嗅板数目、较多数量感觉纤毛和微绒毛,且其嗅囊长径与眼球径比值大于1,这些都揭示了其为＂嗅觉＂鱼类,表现出了对洞穴黑暗环境的适应。

China is the richest country in terms of cavefish species diversity, which brings us excellent materials for studying adapted evolution of cave animals. For instance, most of species from the genus Oreonectes have cave-dwelling behavior. Due to the darkness all the time, cave is an extreme environment for organisms. To adapt this dark environment, cavefish always has degenerated eyes. On the contrary, other sensory organs including olfactory organ have been developed for satisfying the needs of their normal life. Therefore, we chose cave-dwelling loach, O. polystigmus, as a target species to study the structure of the olfactory epithelium. For getting more knowledge and data on its morphological adaptation to cave dark environment, we observed the olfactory epithelium of four individuals of O. polystigmus by using a scanning electron microscopy（SEM）. The olfactory organs of O. polystigmus are oval and lie in the olfactory chamber. The average length of olfactory sac is 2.27 mm, 1.36 times of eye diameter, which revealed that O. polystigmus is a kind of ＂olfactory sensation＂ fish. The olfactory apparatus has 22 to 24 primary lamellae arranged on both sides of a narrow raphe. Each lamella has developed tongue-like structure（PlateⅠ： 3）. Non-sensory cilia are continuously distributed on the lamellae（PlateⅠ： 4）, more on the terminal and the middle of lamellae than the area closed to the raphe, where has many folds with plenty of tiny pores（PlateⅠ： 7）. Sensory cilia mainly locate in the area with thin non-sensory cilia（PlateⅠ： 8）. Microvilli are always distributed under non-sensory cilia（PlateⅠ： 9）. The number of pits on the lamellae located in the middle of raphe is more than that on the lamellae of the anterior or posterior raphe. And on the same lamella, pits on the place close to raphe are denser than those on anywhere else. There is a clear boundary between bare and non-bare regions on the lamella and raphe. Generally, no sensory cilia and microvilli on the raphe are distributed in the grooves of non-bare region. Areas of bare and non-bare regions on the raphe are almost equal（PlateⅠ： 7）. Epithelium of raphe is formed to a series of polygons by continued microridges（PlateⅠ： 10﹣12）. Olfactory sac belongs to G-type, defined by Yamamoto, and always plays an important role in the teleost. Due to the existence of plenty of non-sensory cilia and a certain amount of sensory cilia and microvilli on the lamella and raphe, O. polystigmus is a typical fish relying on the sense of smell in their life. Moreover, isosmate is the hydrodynamic mechanism for O. polystigmus, revealing its adaptation from another angle.