日本鳗鲡早期阶段耳石日生长轮形成的周期

PERIODICITY OF INCREMENT FORMATION IN THE OTOLITHS OF LABORATORY-REARED ANGUILLA JAPONICA LARVAE

于1990年4月从江苏太湖搜集日本鳗鲡亲鱼暂养在天津滨海虾场8t玻璃钢水槽中，经人工催熟催产后孵出仔鳗，对孵出仔鳗连续取样；于1989年4月在长江口采集白仔鳗，观察和比较二者的耳石生长轮形成。结果表明，（1）人工繁殖仔鳗耳石第一个生长轮是在孵出后第一天形成的，轮纹形成具有24h周期性；仔鳗孵出后生长天数与生长轮数关系的回归方程以y=0．23＋0．91x表示，其中，x为孵出后的天数，y为生长轮数;在人工繁殖仔鳗耳石上没有观察到“孵化标记”轮。（2）白仔鳗耳石中心核与“孵化标记”轮之间存在日生长轮。（3）人工繁殖仔鳗与白仔鳗耳石中心核同第一个生长轮比较表明，前者小于后者。

The present paper deals with the periodicity of daily increment formation in the otoliths of laboratory-reared larvae obtained by artificial inducement of repro-duction in parent eel collected from Tai Hu Lake in 1990 and the first ring deter-mination in the otoliths of A. iaponica elvers from the Changjiang River Estuary in 1989. Results were as ffollow.Laboratory-reared larvae survived 16 days.The regression equation of chronological age based on the number of daily inc-rements is y = 0.23+0.91x (r = 0.99, N = 37), where y is the daily number of increments and x is the days after hatching. The daily deposition of increments in the otoliths was verified. No hatch check (heavy dark check) was observed around the nucleus of the otoliths in laboratory-reared A. iaponica.Diameters of the nucleus and the first increment in the otoliths of laboratory-reared A. japonica larvae and field-collected A. japonica elvers were 4.5±0.90μm,6.4 ±0.90μm (N = 41 ) and 4.82±0.84μm, 7.68 ±1.14μm (N = 37) respectively. The diameter of the nucleus and the first increment in the otoliths of field-collected A.iaponica were larger than those of laboratory-reared ones. There is the increment between the nucleus and hatch check ring in the otoliths, and the hatch check ring was not the first increment in the otoliths of field-collected A. iaponica elvers.