长江口日本鳗鲡鳗苗对底质颜色和光照强度的选择行为

摘要

Purpose:The paper is to investigate selective behavior of Anguilla japonica glass eel for environmental factors,to offer a guide for management and protection of Japanese eel stock. Materials:Anguilla japonica glass eel [(57.52 ±2.61)mm,(0.115 ±0.025)g ]captured from the Yangtze Estuary in April 2014 was kept for 2 weeks in an aquarium,and fed to satiation twice a day at 8∶00 am and 18∶00 pm.The temperature and dissolved oxygen of the breeding water was controlled at (25 ±1)℃and 7 mg·L-1 respectively,and water ammonia nitrogen was less than 0.01 mg·L-1 . Methods:The experiment for preference of substrate color and light intensity used individual (30 ind) and population glass eel (30 ind ).Individual experiment index was defined as the percentage of glass eel active time in each area.Population experiment index was defined as the percentage of glass eel number active in each area.In preference for substrate color experiment,we set two light conditions as indoor illumination (88 lx)and dark (0.3 lx),which corresponded to black and white substrate color separately.In preference for light intensity experiment,we set four light intensities as 6 000 -12 000 lx (area A),700 -1 400 lx (area B),60-150 lx (area C),5 -10 lx (area D). Results:The experiment of preference for substrate color results showed that whether in indoor light (88 lx)or dark (0.3 lx)light,individual and population glass eel showed significant (P<0.05)preference for black substrate.The results of individual light intensity preference showed that the percentage of glass eel active time in area A,B,C and D was (3.55 ±7.03)%,(7.31 ±9.34)%,(20.42 ±8.56)% and (68.72 ±17.17 )%,respectively.The results of population light intensity preference showed that the percentage of glass eel number active in area A,B,area C and area D was(2.00 ±4.00)%,(4.00 ± 4.90)%,(21.00 ±9.43)% and (73.00 ±13.45)%,respectively.The active time percentage and number percentage of glass eel active in area D were significantly higher (P<0.05 )than in other areas, which indicated that glass eel obviously selected low light intensity of 5 -10 lx area. Conclusions:In this paper,glass eel showed obvious preference for black substrate and low light intensity of 5 -10 lx.It was speculated that glass eel may select benthic living in low light intensity when migrating upstream through the Yangtze Estuary.The behavior in this paper indicates that glass eel may migrate by tide at night avoid predators on day light for effective migrating to upstream.%采用个体和群体相结合的实验方法，研究了长江口日本鳗鲡（Anguilla japonica）鳗苗对底质颜色和光照强度的选择行为。结果表明：在室内光照（88 lx）和黑暗（0．3 lx）条件下，鳗苗在个体和群体实验中对黑、白底质颜色的选择均有显著性差异（P＜0．05），其对黑色底质有明显偏好。鳗苗对4个光照强度梯度：6000～12000 lx（A区）、700～1400 lx（B区）、60～150 lx（C区）和5～10 lx（D区）的选择性也表现出显著性差异，实验中个体和群体在D区活动的时间和数量百分比均显著高于其它区域（P＜0．05），表明日本鳗鲡鳗苗对5～10 lx的弱光有明显趋性。由长江口日本鳗鲡鳗苗趋向黑色底质和弱光环境的结果推测，长江口鳗苗可能营底栖生活，白天强光照期间栖息于河口区光照强度较低的底层，并于夜间借助潮汐能进行溯河洄游，同时具有躲避敌害、避免被捕食的作用，以尽快适应生态环境变化并成功快速进入淡水水域育肥。