Morphological differences and discriminant analysis of different sex in early stage of <italic>Cynoglossus semilaevis</italic>

Abstract

In order to test the method of culling male and pseudomale seedlings of <italic>Cynoglossus semilaevis</italic> at 70 dph according to morphological differences between different sex to improve the female percentage in the population, a total of 349 seedlings of <italic>Cynoglossus semilaevis</italic> at 70 dph were randomly collected from a farm in Tianjin in 2019. Genomic DNA were extracted from the tail fin of each sample, and the sex specific gene loci of <italic>Cynoglossus semilaevis</italic> were used to accurately identify the genetic and physiological sex of each sample. In order to eliminate the influence of individual differences on the data and facilitate the difference comparison and data continuity, the data were standardized, and the angle value was converted into length by tangent for analysis. A total of 5 morphological traits were obtained, including full length (FL), body height (BH), full length/body height (FL/BH), caudal angle tangent (CT), dorsal at a horizontal angle tangent (DT). Principal component analysis was performed to analyze the morphological variation among different gender groups of <italic>Cynoglossus semilaevis</italic>. The discriminant equations of <italic>Cynoglossus semilaevis</italic> at 70 dph were established for female, male and pseudomale with linear discriminant analysis, and the accuracy of discriminant equations were verified according to the genetic gender information of the established equations. Results showed that the morphological traits of each gender group were normally distributed, and homogeneous in variance (<italic>P</italic>>0.05). The analysis of variance and principal component analysis of morphological characters of <italic>Cynoglossus semilaevis</italic> showed that the differences between males and females were mainly concentrated in body length and body height, and the mean values of body length and body height of females were higher than those of males and pseudomales. The discriminant accuracy of females and males was 37% and 85%, respectively by using various standardized indicators. It was very difficult to discriminate pseudomales, because they were close to males. Results showed that the accuracy of male identification was relatively high, which could meet the requirements of early gender observation and identification of seedlings to improve the female percentage of <italic>Cynoglossus semilaevis</italic>. Therefore, it is suggested to postpone the culling of seedlings of <italic>Cynoglossus semilaevis</italic>, such as at 120 dph, when the sex of the fish is completely differentiated. But it will increase the breeding costs simultaneously, therefore, tradeoff should be considered comprehensively to maximize the benefits.