Studies On Otolith Microstructure Of Larval And Juvenile Ancherythroculter Nigrocauda

During June 2007 to March 2008, otolith microstructure of hatchery-reared Ancherythroculter nigrocauda larva and juveniles were studied by using 1460 fish specimens, which occurred only in the upper reaches of the Yangtze River. Three parts of research were included in this study and he main results were decribed as follows:1. Newly hatched larvae were dressed scales on the whole body on the 55^th day after hatching. The development process experienced four-day-long yolk-sac larvae, 40-day-long post larvae and 15-day-long juveniles stages. The optimal relatinship of total length and daily age is L=6.2705e^0.0316t (R²=0.9502,p<0.01, N=560).2. The newly hatched larvae had two pairs of otoliths, which were sagitta and lapillus. Asteriscus and one swimming bladder appeared on the 13^th day after hatching, meanwhile sagitta was ellipse with sharp aragonite crystal in the front, lapillus was ellipse, asteriscus liked a blob of dropping water when firstly obtained, with sharp aragonite crystal appeared in the ventral. Ventral fins emerged on the 19^th day, and rostrum appeared on sagitta, the protuberance on dorsal of lapillus was obviously, and sharp aragonite crystal on the asteriscus disappeared. When fin fold degenerated on the 26^th day, sharp aragonite crystal appeared in the ventral on sagitta and lapillus had rostrum in the front. On the 41^th day when the juvenile scale appeared, sagitta had dorsal in the dorsal and postrostrum of asteriscus appeared. On the 55^th day when scale covered on the surface of juvenile, the sagitta changed to anomaly-clubbed, lapillus appeared in kidney-shaped and the shape of asteriscus became erose with leafed aragonite crystal in the dorsal. The relationships between the otoliths length and fish total length were fitted with binomial models (p<0.01).3. The relationships between length, width and radius of three pairs of otoliths and daily age all fitted binomial model(p<0.01), and the absolute growth rate increased with daily age in despite of obvious lineal relationships. The specific growth rate all changed from 0.05 to 0.10 per day. The interrelationships between the length of otoliths and fish length all fitted binomial functions.4. Each otolith had only one primordium and one nucleus. And the first increment of sagitta and lapillus both formed on the second day. Increments of lapillus and sagitta(before 18 days) deposited daily after the first increment, and the relationships with daily age expressed as follows: N=0.9828t-0.8194(R²=0.9946,p<0.01, N=1120) and N=0.9479t-0.8463(R²=0.9759, p<0.01, N=338). Besides increments, there were hatch check, transition check and yolk-sac check on sagitta and lapillus. The asteriscus was lack of integrality and dimensions in spite of higher clarity.5. The clarity of lapillus increment reduced greatly under continuous illumination (P<0.01) and the radius decreased(0.010.05) and the increment numbers(P>0.05).6. Water temperature has no effects on otolith increments(P>0.05), but affected lapillus increment deposition obviously(P<0.02). The clarity of lapillus enhanced under the water temperature regimes(P<0.01), the space between lapillus increments changed(P<0.01).7. Under the control of feeding periodicity, the lapillus clarity increased(P<0.01), radius reduced(P<0.01), space between increments increased(P<0.01) and the numbers decreased(P<0.01).