湘江鳡仔稚鱼个体和耳石生长发育研究

SOMATIC AND LAPILLUS OTOLITH ONTOGENETIC GROWTH AND DEVELOPMENT IN LARVAL AND JUVENILE ELOPICHTHYS BAMBUSA RICHARDSON IN THE XIANG RIVER

2008年6月至7月间于鳡(Elopichthys bambusa Richardson)的主要繁殖季节在湘江采集鳡仔稚鱼共370尾,耳石分析表明这些仔稚鱼日龄在4—25d间,推算孵化日期为5月27日至6月22日。仔鱼前弯曲期向弯曲期转化时间为第6日龄,弯曲期向后弯曲期转化为第10日龄,后弯曲期向稚鱼期转化为15.5日龄。体长生长和耳石生长均在进入后弯曲期后(12—13日龄)出现1个节点:节点后体长生长速度是节点前的5倍,节点后耳石生长速度是节点前的2倍。早期生活史不同阶段鳡微耳石形态显著改变:前弯曲期耳石为圆形;弯曲期耳石前后轴的生长速度明显超过背腹轴生长,耳石也变为椭圆形;后弯曲期耳石进一步延长,耳石后端形成略尖的突起,耳石呈梨形;进入稚鱼期后,耳石后突起变得较为平滑,耳石形状呈贝形。耳石半径和体长的关系在后弯曲期阶段出现节点,节点前后呈不同的直线关系。

Elopichthys bambusa Richardson is a piscivorous fish distributes widely in the east floodplain waters,China.This fish is a potamodromous species,which grows and matures in the floodplain lakes and then naturally migrates into the at-tached rivers for spawning.E.bambusa used to be a very important commercial species,however,resource of this fish has been dramatically destroyed in most waters due to overfishing and habitat degradations.With the success of artificial breeding of E.bambusa in early 2000s,this species becomes an important aquacultural species and also a target species of stock en-hancement typically in some reservoirs in the middle and lower reaches of the Yangtze River.Mortality rate of fish during early life stage is high for both wild populations and artificial seeding production.An understanding of early growth and de-velopment is essential not only for wild population conservation,but also for artificial seeding production.In this study,a total number of 370 larval and juvenile E.bambusa was collected in the Xiang River from June to July,2008.Otolith analysis revealed that age of the specimens ranged from 4—25 days,and the back-calculated hatch-ing dates were during May 27th to June 22nd.The mid-age of stage transition from preflexion to flexion was at the 6th day;from flexion to postflexion was at the 10th day;from postflexion to juvenile was at the 15.5th day.Piecewise regression revealed a knot in the growth functions of either body length or otolith radius,were both at the early postflexion stage（the 12nd—13rd day）： the growth rate after the knot was 5 times and twice of that before the knot for body length and otolith radius respectively.The shape of lapillus was round in the preflexion stage;in the flexion stage,the ante-rior-posterior axis growth significantly exceeded along the dorsal-ventral axis,and the shape became oval;the otolith further elongated in the postflexion stage,and the peak of the posterior emerged to shape the whole lapillus pear;in the juvenile stage,the peak smoothed and the shape was mussel.Otolith shape and microstructural analyses can provide essential information revealing the critical events in the early life history of E.bambusa.