半滑舌鳎仔、稚鱼视网膜结构与视觉特性

Structure of retina and visual characteristics of the half-smooth tongue-sole Cynoglossus semilaevis Günter

对1-50d半滑舌鳎仔、稚鱼视网膜和全长50mm的半滑舌鳎幼鱼视网膜结构和视觉特性进行了研究。结果表明:(1)3d仔鱼色素层形成,15d仔鱼没有显著的视网膜运动反应,25d时具有正常感受自然光的明视功能,43d半滑舌鳎稚鱼适应自然光的功能丧失;(2)半滑舌鳎仔鱼阶段感受细胞主要为高密度的单锥,视杆细胞和双锥细胞出现的较晚;单锥融合成双锥时,由于半滑舌鳎视锥细胞椭圆体细长,融合程度较差,尽管在视网膜横切面上能够看到双锥,但在切向切面上仍呈现单锥排列方式;随其生长发育,视锥和神经节细胞密度降低,视杆细胞密度增加,31d后视杆细胞数量显著增加;同时,外核层细胞核与神经节细胞的比值增大,网络会聚程度提高;相关数据表明,20-31d是视网膜结构和视觉特性发生明显变化的过渡时期,这是与半滑舌鳎从浮游生活到底栖生活生态环境的变化相适应的;(3)半滑舌鳎内核层结构特殊,50mm时只有1层水平细胞,属感光系统不发达类型,双极细胞和无长突细胞共4-5层,但不可分辨;内核层细胞层数的减少,基本上没有分化的水平细胞、双极细胞和无长突细胞,说明半滑舌鳎视网膜的光敏感性不高;(4)半滑舌鳎仔鱼浮游生活阶段视敏度较高,视觉在捕食行为中具有重要意义;底栖生活后,视敏度和光敏感性都较差。

The structure of the retina and visual characteristics of half-smooth tongue-sole Cynoglossus semilaevls from newlyhatched larvae to 50-day old juveniles, and at 50 mm total length （TL） young fishes, were exarained. The main results obtained are as follows. （ 1 ） At 3 days from hatching, the eyes are deeply pigmented and the visual system is morphologically complete. At 15 days larvae, the retinomotor responses do not appear obviously. At 25 days, the retina of C. semilaevis can be adapted normally to sunlight, however, at 43 days, the function does not exist. （2） The retina of C. semilaevis in larva consists mainly of single cones （SC） as sensory cells with a high density; the rods and twin cones （TC） appear lather late. Owing to the ellipsoid of cone of C. semilaevis is spindly, when single cones are inoseulated to twin cones, single cones are not well-inoseulated, though twin cones could be seen on the cress-section the retina of C. semilaevis, it is difficult to see twin cones on the tangential section the retina of C. semilaevis.Over the whole range of development, the density of cones and ganglion cells decreases while the density of the rods increases correspondingly, after 31 days, the density of the rods increases remarkably. At the same time, the ratio of nuclei of the outer nuclear layer to ganglion cells increases distinctly. Also, the degree of the assembled meshwork is increased markedly. The data concerned shows that the structure of the retina apparently changes in the stage between 20-and 31-day old juveniles, which is a transitional period in which its visual characteristics changes obviously. It is revealed that the changes of visual structure of C. semilaevis are adapted to the ecological shift from pelagic to benthic habitats. （3） The structure of the internal nuclear layer of C. semilaevis is highly peculiar： a 50 ram C.semilaevis has only a layer of horizontal cells, its sensitization system is underdeveloped. In addition, it has 4 - 5 layers of bipolar cells and amaerine cells. However, it is difficult to distinguish the two kinds of cells. Obviously, the decrease in layers of the internal nuclear layer as well as bipolar, amacrine and ganglion cells, which are not well-differented, showing that the retina of C. semilaevis is not sensitive to light. （4） The acuity of larvae in the pelagic stage is comparativdy high, vision play a very significant role in feeding behavior. After benthic habitats, both the acuity and the light sensitivity are weak, therefore, vision does not have an important effect on feeding behavior.