鲐鱼幼鱼耳石日轮的初步观察与研究

A PRIMARY OBSERVATION AND STUDY ON THE DAILY INCREMENT IN OTOLITH FOR JUVENILE JAPANESE MACKEREL PNEUMATOPHORUS JAPONICUS

对长江口海区鲐鱼幼鱼耳石标本的扫描电镜观察发现，鲐鱼耳石上存在着宽度为数微米到十几微米的细微轮纹，通过对其中３尾鲐鱼的耳石不同放大倍数图像的拍摄，再根据照片对耳石上轮纹和耳石轮纹辐射半径的测量、计数和计算，得出３尾鲐鱼耳石轮纹的平均宽度分别为９．５２、８．５２和８．５７微米，耳石轮纹辐射半径分别为１２６２．２、１１６４．８和１１８７．５微米，由此计算得出的耳石轮纹数分别为１３３、１３７和１３９轮。根据鲐鱼生长方程由鲐鱼体长换算的日龄和根据鲐鱼产卵期推算的鲐鱼幼鱼的生长期都与上述轮纹数相近，表明鲐鱼耳石上的细微轮纹是日轮。

The microstructure of otolith from Japanese mackerel was observed under a scanning electron microscope. Growth increments with width from a few microns to more than 10 microns were observed. Photomicrographs were taken for otoliths of 3 fishes. The average growth increment width and otolith radius were caculated to be 9. 52/1262. 2 μm, 8. 52/1164. 8μm and 8. 57/1187. 5μm respectively by measuring the photomicrographs. based on these results, the numbers of growth increment were estimated to be 133, 137 and 139 respectively. Meantime, the ages of fishes were also estimated acording to the length-growth function and the capture date and the spawning season. these ages were close to the estimated nubers of growth increment, which suggeated that the growth increments were basically formed daily.