依耳石显微结构判断安氏新银鱼的早期生活史

安氏新银鱼的矢耳石呈不规则卵圆形。60尾样品(体长37~52 mm)耳石长半径y与体长x呈线形关系,y=260.335+2.6234x。光镜下观察了耳石制片的显微结构。耳石中心圆形的核平均直径(25.17±2.40)μm(SD,后同)。核中心原基平均直径(7.80±2.22)μm。核周围为同心环纹,即日轮。耳石上日轮数73~101,78.3%的样品分布于83~97日轮范围内。前10个日轮平均间距最窄,为1.76μm,之后日轮间距逐渐增宽,60~70日轮平均间距最宽(2.70μm),而后日轮间距又变窄。依日轮间距推算的体长生长,前10日龄平均日增长0.34 mm,以后生长加快,60~70日龄平均日增长最快,为0.52 mm。依据采样日期,日轮数和胚胎发育期推断,样品鱼的产卵期为4月中旬至5月中旬,出生日期为4月下旬至5月下旬。从最初2~3个日轮间距最宽,4~10日轮间距较窄判断,其卵黄营养期为3~4 d,混合营养期为6~7 d。部分样品在48~72日轮处有过渡轮,应是由近海(盐度27~30)到河口(盐度6~18)盐度急剧变化诱导形成的,表明幼鱼有到河口摄食洄游的习性。

Early Life History of Andersson's Icefish(Neosalanx anderssoni)Inferred by Otolith Microstructure

The Andersson's icefish Neosalanx anderssoni has unregular round saggittae whose long radius Y(μm)was linearly related to the fish body length x(SL,mm), with the equation from 60 individuals(SL 37～52 mm)of y＝260.335+2.6234x,r＝0.3096. The microstructure of the sagittae showed that the mean diameters of core and primordum were(25.17±2.40)μm and(7.80±2.22)(SD) μm, respectively. There were from 73 to 101 rings showing daily growth increment in the otolith in 60 individuals, 78.3% of the individuals being between 83 and 97. The 1st-10th mean daily growth increment was 1.76 μm in width. Since then, its width gradually increased, with the maximum of 2.7 μm at 60～70 daily growth increment. After then, it gradually reduced with the minimum growth of body length from the first day to the tenth day(mean 0.34 mm)calculated on the basis of width of daily growth increment, the maximum occurring at 60-70 day old. The spawning period occurred from 15 April to 15 May and hatched about 10 days late based on the number of daily growth increment in the otolith and sampling time. There were 3～4 days of yolk nutrition and 6～7 days of mixed nutrition inferred by width from 1st to 11th daily growth increment. There was migration habit from inshore to estuary for searching food in the juveniles determined on the mark rings formed by induction of suddenly change in salinity(from 27～30 to 6～18).