Obeservation on otolith of Eleutheronema rhadinum

A total number of 192 samples of Eleutheronema rhadinum were collected from the coastal waters of Qidong in Jiangsu Province,Dongshan Island in Fujian Province,Zhanjiang in Guangdong Province,Haikou in Hainan Province,Taiwan province from February,2010 to May,2012.Length,width,weight,perimeter,area,rectangularity,form factor and density of otolith collected were analyzed.The results indicated that all the sagittal otoliths had rostrum and antirostrum with obvious centural notch,and the ostium was wider than the cauda,rostrum and antirostrum.The shape of sagittal otoliths of samples with shorter fork length was like melon seeds and the outline of the margin was regular,but those with longer fork length showed long and narrow leaf shape with margin bulge like waves.Comparison of sagittal otolith characters between Mugiliformes and Perciformes indicated that: morphology of E.rhadinum sagittal otolith was closer to Perciformes,which supported that E.rhadinumbe belonged to polynemidae,Perciformes.The sagittal otoliths had a length of 2.66%-5.41% of their fork length and a weight of 0.06‰-0.59‰ of their body weight.The density,rectangularity,form factor was 0.80 mg·mm-3,0.70 and 0.58,respectively.The morphological stability of sagittal otolith was remarkably higher than that of their body shape.The variation coefficients of the length,width and weight of sagittal otoliths were smaller than those of the fork length and body weight.Sagittal otolith measurements(otolith length,width,weight,length-width ratio) were significantly related to the standard fork length,and otolith length and the otolith width followed a power function.Density,rectangularity,form factor,OL/FL,OWe/BW can be used as typical characters to measure the body shape of Eleutheronema rhadinum.