| The present paper deals with the periodicity of daily increment formation in the otoliths of laboratory-reared larvae obtained by artificial inducement of reproduction in parent eel collected from Tai Hu Lake in 1990 and the first ring determination in the otoliths of A. japonica elvers from the Changjiang River Estuary in 1989. Results were as follow.
Laboratory-reared larvae survived 16 days.
The regression equation of chronological age based on the number of daily increments 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. japonica.
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±0.90 μm, 6.4±0.90 μm (N = 41) and 4.82±0.84 μm, 7.68±1.14 μm (N = 37) respectively. The diameter of the nucleus and the first increment in the otoliths of fie1d-collected A. japonica were larger than those of 1aboratory-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. japonica elvers. |
