Use left or right otolith for shape analysis in Schizothorax grahami?

Abstract

Lots of studies using otolith microstructures to divide fish stocks only select one of the left and right otoliths as the object, and the difference between the left and right otoliths has not been considered in detail. In this paper, we used Shape Index method and R language to compare the microstructures of the left and right asteriscus otolith of Schizothorax grahami (Regan, 1904) in the source section of Chishui River. The paired t-test results of otolith morphological index showed significant difference between the roundness (P < 0.05), and the Mann-Whitney U test results showed significant difference between circularity (P < 0.05) and format-factor (P < 0.05). The results of principal component analysis showed that the eigenvalues of two principal components are greater than 1, and the cumulative contribution rate of the first two principal components was 72.84 %. In the first principal component, except for the rectangularity, the other shape indexes were greater than the second principal component, which reflected the degree of difference between the long and short axes, and the irregularity of the contour. The results of ANOVA in R language showed that there was no significant difference in Fourier coefficients of the left and right otoliths (P > 0.05). At the same time, according to the average shape reconstructed by wavelet coefficient, the contours of the left and right otoliths were symmetrical. The values of the left and right sides based on the wavelet coefficient were symmetrically distributed on both sides of the origin, while based on the Fourier coefficient were clustered in the center of the origin. Through the two analysis methods, it is indicated that there is no significant difference between the left and right aster otolith profiles of S. grahami in the source section of Chishui River. When otolith microstructures were used to classify S. grahami, the selection of a single otolith (left or right) would not affect the analysis results.