Morphological differences of five Eleutheronema rhadinum geographical stocks

In order to explore the morphological differences of Eleutheronema rhadinum in different geographical groups, this paper was based on 133 E. rhadinum individuals collected from Haimen, Rudong, Zhoushan, Sanmen and Zhuhai from 2018 to 2019, 35 measurable traits and 8 countable traits were measured, and photos of preserved samples were taken for geometric morphological analysis. In the traditional morphological analysis, ANOVA results showed that there were significant differences in other factors except the anal length/body length. Principal component analysis results showed that the variance contribution rates of the first three principal components were 27.724%, 23.959%, 13.535%, and 65.218%. Cluster analysis results showed that there was no significant morphological difference among geographic groups. In the geometric morphology analysis, the results of overprint analysis showed that the marks 5, 4, 7, 7 and 9 had a great influence on the external morphology of E. rhadinum. The results of principal component analysis showed that the first three principal components contributed 21.25%, 18.41%, 12.60% , and the cumulative contribution was 52.25%. The results of principal component cluster analysis showed that there was no morphological difference. In the typical variable analysis results, CV1 contributed 71.059%, CV2 contributed 18.192%, and CV1 and CV2 plotted the two-dimensional scatter diagram of typical variables with staggered distribution of each group sample. The results of Mahalanobis distance and Przewalski distance of different geographical groups showed that there were no significant morphological differences among different geographical groups.The results of both traditional morphology and geometric morphology analysis showed that the morphological characteristics of E. rhadinum among 5 geographical groups were different to a certain extent, and were positively correlated with geographical distance, but had not yet reached the level of population differentiation. This may be due to the geographical isolation between the South China Sea and the East Yellow Sea caused by the fall of sea level during the Pleistocene Glacial Age. However, with the rise of sea level at the end of Pleistocene, because of the strong migration habit of E. rhadinum, some groups could still migrate long distance between the Yellow Sea and the South China Sea, and the presence of fish eggs and larvae that spread with ocean currents, resulted in different levels of gene exchange between populations. As a result, although there are differences in morphological characteristics among different geographical groups, the morphological and genetic differentiation still cannot reach the level of population differentiation.In view of the time difference of E. rhadinum reproductive migration of different geographical groups in the corresponding sea areas, it was suggested that these 5 geographical groups be divided into 1 management unit of Sanmen group, 1 management unit of Zhoushan group, 1 management unit of Rudong group and Haimen group, and another independent management unit of Zhuhai group. In order to protect the sustainable development of fishery resources and guarantee the livelihood of fishermen, targeted management policies should be further formulated and implemented according to four management units for five geographical groups.