| Eleutheronema rhadinum，widely spread euryhaline fish in the southeast coastalareas of China, has advantages such as growing fast, taste good, which has obviouslyhigh economic profit and has a wide market prospect. But there are few researchcontents about E. rhadinum stock structure, age composition and otolith morphology. Inthis research, we acted E. rhadinum collected from the coastal waters of Qidong inJiangsu Province, Dongshan Island in Fujian Province, Zhanjiang in GuangdongProvince, Haikou in Hainan Province, Taiwan province from February,2010to May,2012as the research object. We studied their otolith morphology, stock structure andages. This research provides some theoretical basis for the further development of E.rhadinum. The main findings are as follows:1、Observation on otolith morphology of Eleutheronema rhadinumA total number of192samples of Eleutheronema rhadinum were collected fromthe coastal waters of Qidong in Jiangsu Province, Dongshan Island in Fujian Province,Zhanjiang in Guangdong Province, Haikou in Hainan Province, Taiwan province fromFebruary,2010to May,2012. After otoliths collected, length, width, weight, perimeter,area, rectangularity, form factor and density of otolith were analyzed. The resultsindicated that all the sagittal otoliths have rostrum and antirostrum with obviouscentural notch i.e., the ostium was wider than the cauda, rostrum and antirostrum. Theshape of sagittal otoliths of samples with shorter fork length is like melon seeds and theoutline of the margin is regular, but it changes to long and narrow leaf shape graduallywith margin bluge like wavilness. Comparison of sagittal otolith characters betweenMugiliformes and Perciformes indicate that: E. rhadinum sagittal otolith morphology iscloser to Perciformes, which supports E. rhadinum be classified to polynemidae,Perciformes. The sagittal otoliths have a length of2.66%～5.41%of their fork lengthsand a weight of0.06～0.59‰of their body weights. The density, rectangularity, formfactor is0.80mg.mm-3,0.70and0.58, respectively. The morphological stability ofsagittal otolith is remarkably higher than that of their body shape. The variationcoefficients of the length, width and weight of sagittal otoliths are smaller than those of the fork lengths, and body weight. Sagittal otolith measurements (otolith length, width,weight, length-width ratio) were significantly related to the standard fork length, otolithlength was power realated to the otolith width. Density, rectangularity, form factor,OL/FL, OWe/BW can be typical characterization to measure their body shape.2、Geographic variation in otolith morphology of Eleutheronema rhadinumA total number of100samples of Eleutheronema rhadinum were collected fromthe coastal waters of Qidong in Jiangsu Province, Dongshan Island in Fujian Province,Zhanjiang in Guangdong Province, Haikou in Hainan Province from February,2010toMay,2012. After one pairs of sagittal otoliths collected, feature points were set anddistances between points were measured. PCA (principal component analysis), clusteranalysis, stepwise discriminate analysis were carried out based on1100groups of datas.Results indicated that, the shape of sagittal otoliths of Eleutheronema rhadinum waslong and narrow leaf shape and influences by D10/D3and D1/D3. PCA indicated thatthe first three principal components provided83.52%cumulative contribution, the firstand third principal components had realationship with the outline of margine, rostrumand posterior, the second principal component reflects the size of antirostrum. The resultof cluster analysis showed that four samples were divided into3groups, whichindicated that Euclidean Distance has a closed realationship with geographical distances.The results of cluster analysis and stepwise discriminate analysis showed that foursamples could be separated accurately, which indicated that there were morphologicaldifferentiation among four geographical population samples, and results showed thatmorphological of sagittal otoliths can be influenced by environments factors.3、Comparision study of four materials for estimating age of Eleutheronemarhadinum11samples of Eleutheronema rhadinum collected from Dongshan Island in FujianProvince in May,2012were used in this experiment. We Used scales, otoliths, vertebrasand pectoral spines as the main age determination materials. Research results showed:scales of E. rhadinum was cycloid scale and placoid scale, annual ring and radial canalexists in the scale. The annual-ring feature belonged to the loose-close and cut pattern.The shape of sagittal otolith was long and narrow leaf. There were many bright and darkdiffraction annual-rings from the center back side in transmitted light. Each section ofvertebras was both concave, with bright and dark diffraction annual-rings arranged in concentric ring on the top of the cone. Results showed that annual-rings on the thirdvertebra was the most significant. Sections of pectoral spine is triangular, bony tissueenclosing fatty tissue. No annual-rings found on the pectoral fins ridge section. Otoliths,vertebras and scales were suitable materials for E. rhadinum age determination underthe age of five, which had coincidence rate100%,90.9%,90.9%respectively. Andpectoral spine can’t be used as materials for age determination. |
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