Identification Of Carangidae Species In Dongsha Islands Of The South China Sea Based On Otolith Morphological Information

Otolith is an important carrier for fish to store life information.Otolith morphology has species specificity and is widely used in species identification and population identification.With the rapid development of advanced digital imaging technology and high-end image processing system,the study of otolith morphology is becoming more and more mature.The analysis of fish otolith morphology not only provides relevant evidence for the classification of traditional fish external morphology,but also helps to promote the development of fish otolith morphology.Therefore,in this paper,7 kinds of otoliths(Decapterus macrosoma,D.tabl,D.kurroides,Trachurus japonicus,Alectis ciliaris,Caranx equula,Selar crumenophthalmus)were used as examples to identify and classify the otolith morphology by traditional morphometry,landmark method and elliptic Fourier transform method.The effect of species identification is remarkable,which provides a sound classification and recognition mechanism for perfecting the systematic classification and automatic classification of otolith morphology.(1)This study observed and determined the sagittal otoliths morphology of 105 the genus Decapterus(Decapterus macrosoma,D.tabl and D.kurroides)collected from the Dongsha Islands in the South China Sea.The sagittal otolith shape of the genus Decapterus is long oval with developed rostrum,and the differences between species are distinct.The front end of D.macrosoma rostrum is slightly bent downward.The knob of otolith dorsal of D.tabl is obviously developed with serrated shape,and the front end of rostrum is slightly broad and thick.The overall outline of D.kurroides otolith is smoother,and antirostrum is poorly developed.According to the morphological indexes(otolith length,otolith width,rostrum length,rostrum width,otolith weight,otolith area),the classification success of different species of the genus Decapterus(D.macrosoma,D.tabl and D.kurroides)are 100%,100%,and 91.7%,respectively.The results show that sagittal otolith is a kind of material for identifyingthe genus Decapterus,which will provide basis for identifying the genus Decapterus in relevant waters.(2)In order to study landmark-based morphometrics analysis to morphology information of sagittal otolith on extracting effect,the landmark-based morphometrics analysis was carried out,according to the sagittal otoliths of 108 the Carangidae fishes samples(Trachurus japonicus,Alectis ciliaris,Selar crumenophthalmus,Caranx equula)collected from the Dongsha Islands waters in the South China Sea in March 2014.Landmark coordinate values were extracted after otolith shapes digitized by processing image while using relative warp(RW)for principal component analysis(PCA).12 RW values were used to distinguish the otolith shapes among four Carangidae species for discriminant analysis(DA).Visualization of grid deformation by thin plate spline(TPS).The result indicated that the 1st and 2nd RWs accounted for 74.55% and 11.16% of the total variation,respectively.Between landmarks 5,and 4 were important contributors,and could explain 42.655% and 35.853% for the most variation,respectively.Centroid size(CS)of sagittal otolith shapes compared maximum value of four Carangidae species.The Selar crumenophthalmus was the biggest and the Alectis ciliaris is the smallest.The otolith morphology of four Carangidae species on RW-based cross validation analysis(CVA)and stepwise discriminant analysis(SDA)indicated that classification success was 100%.It is shown that landmark-based morphometrics analysis has a significant effect on the identification of morphology information of sagittal otolith,and visualization of otolith shapes provides a scientific basis for automated classification of otolith morphology.(3)In order to study the morphological characteristics of sagittal otolith and sulcus of fish,the elliptical Fourier transform analysis was carried out,according to the sagittal otoliths of 103 the genus Decapterus(Decapterus macrosoma,D.tabl and D.kurroides)collected from the Dongsha Islands waters in the South China Sea from March to May in 2014.The contours of entire otolith morphology and sulcus morphology were extracted into elliptic Fourier descriptors(EFDs)by image processing,and 20 harmonics were obtained by reconstructing the contours of entire otolith morphology and sulcus morphology.The 77 EFDs coefficients were extracted from the contours of entire otolith morphology and sulcus morphology of the genus Decapterus for principal component analysis(PCA)and discriminant analysis(DA).PCA of the entire otolith morphology showed that the 1st and 2nd components accounted for 41.3% and 12.4%of the total variation respectively;while the 1st and 2nd components of sulcus morphology accounted for 33.8% and 30.1% of the total variation respectively.The cross validation analysis(CVA)of entire otolith morphology of three Decapterus species indicated that classification success was 100%,95.7% and 100%,respectively;and the CVA of sulcus morphology indicated that the classification success was 96.4%,95.7% and 95.8%,respectively.It is shown that elliptic Fourier transform analysis has a significant effect on the identification of entire otolith morphology and sulcus morphology of the genus Decapterus.(4)The morphological characteristics of sagittal otoliths of 135 Carangidae(Decapterus macrosoma,D.tabl,D.kurroides,Trachurus japonicus,Alectis ciliaris,Caranx equula,Selar crumenophthalmus)collected from the Dongsha Islands in the South China Sea were studied in this paper.The entire morphology of Sagittal Otolith of 7 species of Carangidae is long oval,quadrilateral and semicircular curved hooked.There are knobs around the otolith with the development of rostrum and sulcus,and the sulcus extends from the excisural notch of the anterior part of otolith to the posterior part of otolith.The results show that the morphological characteristics of otoliths of 7species of Carangidae are obviously different among species.The systematic classification and retrieval table established by otolith morphology and the application of cluster analysis are effective in identifying otolith morphology,which will provide a reference for the stock identification and systematic classification of Carangidae.