仿刺参幼体对底栖硅藻附着基的选择性及其摄食器官发育的研究

Effects of benthic diatom species and density on settlement and ontogenetic development of feeding organs in sea cucumber Apostichopus japonicus

幼体变态附着率低是制约仿刺参Apostichopus japonicus育苗效益的重要因素之一。在水温22.0～26.0℃和盐度为28.0～31.0条件下,在玻璃钢水箱中放入接种圆筛藻Coscinodiscussp.、舟形藻Naviculasp.、双肋藻Amphipteurasp.及其等量组合的波纹板和樽形幼体,研究了仿刺参幼体对底栖硅藻的附着选择性和摄食器官的发育。结果表明:在12 d的培育中,波纹板上稚参的附着数量初期较低,中期较高(6月25日,即第5天),后期又降低,未附着的浮游幼体胃部萎缩成棒状,边缘溃烂,无法附着变态。试验初期,附着在接种双肋藻的波纹板上稚参数量最多,但附着高峰时急剧减少;后期接种舟形藻的波纹板上稚参数量最多,接种双肋藻的最少。附着在波纹板上的稚参数量均随硅藻密度的增加而减少,密度为1万个/cm2时,波纹板上稚参的数量最多,只有圆筛藻+舟形藻+双肋藻组在密度为25万个/cm2时,波纹板上稚参的数量最多。扫描电镜观察发现,刚附着的稚参触手顶部具有可收缩的笼形结构(称摄食笼),笼呈中空状,孔径为(6.7×3.9～17.8×10.2)μm,套住食物后,经"寻食→定位→摸索→靠近→调整和选择→固定→拽拉→吞食"等过程将食物摄入。摄食笼的孔隙间有丰富的黏液状分泌物,具有黏附作用。幼参体长达8 mm时,触手顶端的摄食笼变为4个瓣状结构,瓣的表面上有均匀分布的花瓣状突起;体长为25 mm时,触手顶端由20个环绕口的触手组成,每个触手的顶端有多个瓣状结构,伸展形成"手"似结构,可扫抓兼滤捕食物。文中还讨论了仿刺参摄食器官结构的发育特点和划分稚参及幼参的形态界限。

The low settlement and metamorphism rates are an important factor restricting the production of sea cucumber Apostichopus japonicus.Choice of larvae to different benthic diatoms and the ontogenetic development of feeding organs were observed.There was a trend of less juveniles in the early experiment,more juveniles in the mid-experiment（the fifth day,25th of June）,and less juveniles in the later experiment on the plates.The unsettled larvae had atrophic and edge cankered stomachs.The maximal number of larvae was found on the plate with Amphipteura sp.among the 8 groups in early experiment,and then reduced rapidly since the fifth day while the maximal number of larvae was observed on the plates with Navicula sp.in later stage.There was the least number of larvae on Amphipteura sp.plates.Inverse relationship between the number of settled larvae and the density of benthic diatoms was observed.The maximal larvae settled were found to be on the plates with the diatoms density of 1×10^4 cells/cm^2,except that the group with the mixture of the three diatoms had the highest settlement rate on the density of 25×10^4cells/cm^2.Scanning electronic microscopy（SEM） showed that the newly settled juveniles have feeding cages on the apical tentacles in which there were webs with many sticky meshes with a diameter of（6.7×3.9-17.8×10.2）μm×μm.The early juveniles feed on benthic diatoms by the feeding cages trapping through several processes including search,settlement,touch,approaching,selection,standing,dragging and feeding.As development processes,the juveniles with body length of 8 mm have 4 petal-like protuberances on the apical tentacles which are used for grasping food.For the juveniles with body length of 25 mm,around a mouth there are 20 tentacles on which there are many petal-like protuberances stretching like fingers on the apical surfaces.The protuber ances are used for brooming and grasping,even filtering food.Morphological distinction between early and later juveniles was discussed in detail.