池沼公鱼耳石日轮的观察研究

OBSERVATION ON THE DAILY GROWTH INCREMENTS IN THE OTOLITH OF POND SMELT,HYPOMESUS OLIDUS

于1989年3－8月，从辽阳汤河水库捕取成熟的池沼公鱼，获得人工授精卵。用压片法光镜下连续观察胚胎发育后期和前仔鱼期耳石轮纹的形成，并采集已知月龄的幼、成鱼耳石，制片镜检轮纹数量和排列。结果表明，仔鱼在印黄接近吸收完并开始摄食外界食物时，即孵出后第6d至第7d形成第1个轮纹，之后每天一轮，这些轮纹就是日轮；日轮间距呈规律性变化，这些变化与鱼体生长发育及生态条件密切相关。

This paper reports March-August 1989 studies on the daily growth increment in the otolith of pond smelt (Hypomesus olidus) from Tanghe and Dafengkou Re-servoirs. The sagittal otolith at stages of pre-larvae .and embryo development later was observed by light microscope. The materials were obtained from artificially fer-tilized eggs. There were two growtb increments in otolith of larvae 9 days age after hatching, and increment formation continued on a daily schedule. The first growth increment was deposited during the yolk-sac reabsorption period and feeding began from this time on.The otolith section from young and adults were examined by light microscope and scanning electron microscope for morphology, size, increment counts, width and microstructure of dai1y growth increment. The sagittal radius (OR, mm) was line-arly related to fish length (FL, mm), the equation for 51 individuals was OR =0.0154FL + 0.2812, r = 0.9087, P＜0.01. A single growth increment comprising an incremental zone (light band) plus a discontinuous zone (dark band) was generally formed daily. High magnification revealed the incremental zone's crystalline struc-ture. Based on tbe daily otolith growth increment, the daily age of the fish may be estimated by D = Rn +Ii+K, where D is daily age, R. is number of rings in otolith, It is time (days) from hatching to when feeding began, K is a constant and equal to 1. The change of daily growth increment width was regular and clo-sely related to growth and development of the fish and ecological condition.