| China is the largest producer of eels in the world now. The output ofeels was nearly213800ton in2010, which occupied two in third of thetotal world output. In recent years, due to the decline of eel resources, theprices of larval eel have been steadily rised. In2011and2012, the pricewas nearly35-40yuan each tail which became a veritable “soft gold”.Yangtze River estuary is served as the main production regions of larvaleels. Clarify the basic biological characteristics of the eel is very conduciveto the conservation and sustainable use of the resources.A total of1258Japanese eels larvae were collected at Jingjiang reachof Jiangsu and Jiuduansha of Shanghai in January-April2011and2012, weanalysed pigmentation developmental stages and daily age composition oflarval eels, both body and sagittal otolith morphological parameter weremeasured, we also detected element composition and concentration ofsagittal otolith. The main results are as follows: 1. The larval eels collected in Yangtze River estuary developed at fourpigmentation stages. VA stage was332that accounted for26.4%of theoverall, VB stage was730that accounted for58.0%of the overall, VIA1stage was186that accounted for14.8%of the overall and VIA2was10accounted for0.8%of the overall. VA and VB stages belong to glass eelswhich total of1062accounted for84.4%of the overall. VIA1and VIA2stages belong to elvers which total of196accounted for15.6%of theoverall. The pigmentation developmental stages showed obviouslymenstrual change. With the passage of time, the proportion of glass eelgradually reduced, and the proportion of elvers gradually increased.2. The daily age of Janpanese eels larvae ranged from122.0-190.0dand the average age was150.9±12.7d. There were65.50%larval eels’ agefocued on145.0-165.0d. The daily age of Jiuduansha group ranged from122.0-190.0d (148.8±11.0d), and the Jingjiang group was134.0-185.0d(156.3±13.3d). The average daily age difference of two sampling site was7.5d. ANOVA analysis showed that daily age of Jingjiang group wassignificantly elder than Jiuduansha group (p=0.003<0.050). The averagedaily age of VA stage was144.9±9.0d (130.0-171.0d), VB was149.9±10.3d (122.0-175.0d), VIA1was162.7±12.9d (136.0-187.0d) and VIA2was176.7±12.3d (152.0-190.0d) respectively. The daily age of larval eels atdifferent pigmentation stages showed significantly positive correlations (Spearman, r=0.486, p=0.000<0.01). With the pigment developed from VAto VB stage, the average daily age increased5.0d, then from VB to VIA1stage the average daily age increased12.8d and VIA1to VIA2stageincreased14.0d.3. With growth and pigmentation development, the bodymorphological characteristics change mainly reflected in HD，BB，HB，SL，MD and VDSOPD et al. ANOVA analysis showed that the significantdifference only exist in glass eel stage (VA and VB) and not exist in anyother stage. It meaned that the change of external morphologicalcharacteristics of eels larvae happened when it arrived in the estuary. So,the head of larval eels became narrow and body shape became moreelongated. We meaguered morphological characteristics of211sagittalotolith and spearman correlation analysis showed that there was significantpositive correlation between pigmentation developmental stages and otolithmorphological parameters. With growth and development from VA to VIA2stage, the area of sagiital otolith increased18822.89μm2, the perimeterincreased148.50μm, the otolith length increased46.68μm, the otolithwidth increased38.64μm and the maximum radius increased23.73μm.4. The elements of sagittal otolith that extracted from five larval eelswere detected by using synchrotron radiation X-ray fluorescence (SRXRF).Results showed that fourteen elements could be accurately detected. It included two major elements Ca and Sr, the average contens of which inotolith could reach240215.928μg/g and2383.221μg/g respectively. Theother twelve were recognized as minor elements. Their contentssequentially decreased in the following order: Ba, Fe, Mn, Zn, Cr, Ni, Hg,Se, Co, Cu, Au, V. The average concentrations of Ba, Fe, Mn, Zn were1-10μg/g and the average concentrations of the rest elements Cr, Ni, Hg, Se, Co,Cu, Au, V were less than1μg/g. According to spatial distribution and thecontent variation of all measured elements, Ca and Sr were the most stableelements whose Coefficient of variation were10.11%and21.83%. Incomparison, the Coefficient of variation of Mn, Zn, Cr, Ni, Co varied from23.11%to35.88%and despite that V, Hg, Au, Ba were even beyond50%.The most unsteady element was Se for its Coefficient of variation reached134.31%. We also found that the variation of Sr/Ca ratios were delayed inthe otolith when Japanese eels larvae migrated from sea to freshwater. |
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