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Article

Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein

by
Qiming Wang
1,†,
Suxing Fu
2,†,
Xiaoyi Chen
3,
Yuting Duan
2,
Luo Lei
2,
Yawen Fan
4 and
Chaowei Zhou
2,*
1
Department of Agriculture and Rural Affairs of the Xizang Autonomous Region, Lasa 850000, China
2
College of Fisheries, Southwest University, Chongqing 402460, China
3
General Office of the Xizang Autonomous Region Committee of the Chinese People’s Political Consultative Conference, Lasa 850000, China
4
College of Fisheries, Huazhong Agricultural University, Wuhan 430000, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Fishes 2025, 10(8), 399; https://doi.org/10.3390/fishes10080399
Submission received: 17 June 2025 / Revised: 31 July 2025 / Accepted: 6 August 2025 / Published: 8 August 2025
(This article belongs to the Section Sustainable Aquaculture)
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Abstract

Accurate sex identification is crucial for the artificial breeding of fish species, and identification based on phenotypic traits is the preferred method owing to its low cost and rapidity. This study aimed to investigate morphological differences between male and female Gymnocypris eckloni Herzenstein. A total of 166 G. eckloni individuals (83 males and 83 females) were included, and 20 morphological indicators, including head length, snout length, and body weight, were measured. Various analytical methods, such as correlation analysis, principal component analysis, discriminant analysis, and systematic cluster analysis, were used to compare the morphological characteristics of male and female G. eckloni. The result showed significant differences in morphological characteristics between male and female individuals (p ≤ 0.05). Principal component analysis revealed five main components that collectively contributed to 83.64% of the variance, primarily including body length, fork length, total length, and body weight, highlighting the significance of these components in sex differentiation. Subsequently, a mathematical model was constructed via discriminant analysis. This model demonstrated an accuracy of 79.5% and 73.5% in identifying male and female G. eckloni, respectively, with an overall accuracy of 76.50%. Furthermore, on analyzing the relationship between body length and body weight in G. eckloni, we found differences in growth patterns between sexes. In particular, female fish usually weighed more than male fish, which was consistent with the biological characteristics and energy distribution patterns of G. eckloni. These results suggest that sexual dimorphism in G. eckloni is primarily concentrated in body shape and head morphology, which provides a reliable basis for sex identification based on morphological differences.
Keywords:
Gymnocypris eckloni; sexual difference; discrimination; mathematical model; statistical analysis
Key Contribution: This study aims to address the challenges faced in the artificial breeding of Gymnocypris eckloni Herzenstein, especially regarding sex identification. The innovative approach of our research lies in using morphological indicators to differentiate between male and female G. eckloni. We analyzed 20 different morphological traits of 166 individuals and employed methods like principal component analysis, discriminant analysis, and hierarchical cluster analysis. The results indicate significant differences in body shape and head morphology between sexes, providing a reliable method for sexual identification.

1. Introduction

Gymnocypris eckloni Herzenstein, a member of the family Cyprinidae and the subfamily Schizothoracinae, predominantly inhabits the unique hypoxic environments of the upper Yellow River and Qinghai Plateau at an altitude of 3750–4750 m. This fish species is endemic to China and plays a crucial ecological role within the ecosystem of the Yellow River basin [1,2,3,4,5]. Notably, it possesses significant application prospects owing to its high edibility [6,7,8] and specific medicinal properties. For instance, its bile can be used to treat sores, cataracts, and burns; its bones have the effect of diuresis and swelling; and its muscle can clear the intestines and remove blockages, draining pus, generating new muscles, removing heat, and promoting detoxification [9]. As a representative species of Schizothoracinae, G. eckloni exhibits typical characteristics of high-altitude fishes, such as slow growth, delayed sexual maturity, and low reproductive capacity [1,10,11,12]. In recent years, the natural habitats of G. eckloni have undergone substantial changes owing to the construction of hydraulic engineering projects [13,14,15,16,17]. Additionally, the increasing presence and diversity of invasive species and the slow growth, delayed sexual maturity, and low reproductive capacity have dramatically reduced the population of G. eckloni [17,18,19]. Therefore, increasing the population of G. eckloni through selective breeding is necessary for conserving fishery resources [20,21].
Since the development of artificial breeding for fish, it has been widely used in large-scale G. eckloni production. Artificial breeding provides an essential material basis for the sustainable development of aquaculture [22,23,24]. An essential aspect of artificial breeding for fish is the accurate identification of the sex, which promotes the feasibility of large-scale production. Molecular markers can be used to identify male and female fish from a genetic perspective [25,26,27,28]. However, their high costs and advanced technical requirements limit their widespread application in artificial breeding [29,30,31]. Sex can be determined through anatomical observation and pathological examination of gonadal tissue slices; however, this approach requires dissection of the fish body, which does not conform to the purpose of artificial breeding [32]. Ultrasonic technology has been used to assess gonadal development and identify sexually mature male and female sturgeons; however, it does not provide sufficient practical information [33,34]. Therefore, the abovementioned sex identification methods cannot be widely used in the artificial breeding of fish species. Since the use of morphological [35,36] and phenotypic [37,38,39,40] assessment methods in the 1980s, many scholars have used these methods to study biological evolution, community structures, species differentiation, and sex-specific differences within species [41,42,43,44,45,46].
In recent years, studies have investigated sex-specific morphological differences in various fish species, including Cynoglosus abbreviatus [47], Larimichthys crocea [48], Scatophagus argus [49], Erythroculter ilishaeformis [50], Paramisgurnus dabryanus [51], Odontobutis potamophila [52,53], Mastacembelus armatus [54], Siniperca chuatsi [55,56], Takifugu fasciatus [57], and Acrossocheilus hemispinus [58]. Their research indicates that morphological analysis can distinguish between male and female fish. However, to date, no studies have explored the sex-specific morphological characteristics of G. eckloni. If morphological measurements can be used to distinguish between males and females of G. eckloni, this will greatly reduce the breeding costs of G. eckloni. In this study, we used a multivariate morphological assessment method to analyze morphological differences between male and female G. eckloni and constructed a mathematical model to discriminate between male and female fish, aiming to provide a theoretical basis for the selection and breeding of parental species for sex identification.

2. Materials and Methods

2.1. Experimental Materials

A total of 166 G. eckloni individuals, aged 6–7 years and intended for artificial breeding, were randomly selected from Tianquan Chuanze Fishery Co., Ltd. (Coordinates: 102°52′41.24″ E, 30°0′17.62″ N), Tianquan County, Sichuan Province, China, in May 2022. After image acquisition, the sex of each fish was confirmed via dissection.

2.2. Data Measurement

After the fish were anesthetized with 30-g/M3 m-aminobenzoic acid ethyl ester methane sulfonate (MS-222), the body surface was blotted dry with a towel and filter paper. The body weight (M) of each fish was measured using an electronic scale with an accuracy of 0.01 g. The Gooal-HiTIP phenotype analysis system (FS2000, Wuhan Gooal Gene Technology Co., Ltd. Wuhan, China) was used to capture images of the anesthetized fish and measure 20 morphological indices accurate to 0.01 cm (Figure 1) [47,48]. These indices included overall length (AI; X1), fork length (AH; X2), body length (AG; X3), trunk length (DE; X4), the distance from the cloacal aperture to the base of the pectoral fin (ON; X5), the distance from the base of the pectoral fin to the base of the ventral fin (NR; X6), the distance from the base of the ventral fin to the base of the anal fin (PR; X7), the distance from the cloaca to the base of the ventral fin (OR; X8), the distance from the cloaca to the base of the caudal fin (OS; X9), body height (LM; X10), head length (AD; X11), anal fin length (PQ; X12), caudal fin length (GI; X13), body thickness (X14), head breadth (X15), caudal peduncle length (FG; X16), head length behind the eye (CD; X17), caudal peduncle depth (JK; X18), snout length (AB; X19), and eye diameter (BC; X20).To eliminate the effects of individual sizes of the fish on these indices, the head morphological data (head width, head length behind the eye, snout length, and eye diameter) were divided by head length, the caudal peduncle depth was divided by body depth, and other morphological data were divided by body length for standardization.

2.3. Data Processing

This study employed Pearson’s correlation matrix to explore the correlations among various morphological traits of Gymnocypris eckloni, utilized principal component analysis (PCA) to reduce the dimensionality of its morphological traits, established a discriminant function based on primary morphological shapes, and finally validated the reliability of the discriminant analysis results using systematic cluster analysis. Correlation analysis, principal component analysis, discriminant analysis, and systematic cluster analysis were performed on collated data using SPSS (version 26.00; International Business Machines Corporation; Northampton, NY, USA), Origin Pro (version 2024; OriginLab Corporation; Armonk, MA, USA) software, and Python (version 3.11.8; Python Software Foundation; Beaverton, OR, USA). SPSS (version 26.00) was used to organize the data, Origin Pro was used to construct dendrograms to demonstrate the results of cluster analysis, and Python (version 3.11.8) was used to perform correlation and cluster analyses on various morphological traits and construct a correlation-based clustering heatmap. Through these analyses, traits with significant differences between male and female G. eckloni were identified and an equation for discriminating between male and female individuals was established. The relationship between body length and body weight in G. eckloni was described using the following equation: B W = a × S L b . In this equation, BW represents body weight, SL represents body length, a represents the conditioning factor, and b represents the allometry growth factor [59,60].

3. Results

3.1. Comparison of the Morphological Traits of Male and Female G. eckloni

The statistics of the morphological traits of male and female G. eckloni are presented in Table 1 and Figure 2. In male fish, the top five traits revealing the most significant variation were body weight, eye diameter, caudal peduncle length, anal fin length, and snout length, with the coefficients of variation being 23.05%, 13.74%, 11.92%, 11.54%, and 10.92%, respectively. In female fish, the top five traits revealing the most significant variation were body weight, snout length, eye diameter, head length behind the eye, and anal fin length, with the coefficients of variation being 22.15%, 15.89%, 14.4%, 12.58%, and 10.72%, respectively. Trunk length, the distance from the cloaca to the base of the caudal fin, anal fin length, body width, head width, caudal peduncle length, caudal peduncle height, and body weight showed more significant variations among male fish than among female fish, whereas the remaining traits showed more significant variations among female fish. The multivariate analysis of variance (MANOVA) revealed highly significant differences (p ≤ 0.001) were observed in 17 traits between male and female fish. These traits included overall length, fork length, body length, trunk length, the distance from the cloacal aperture to the base of the pectoral fin, the distance from the base of the pectoral fin to the base of the ventral fin, the distance from the base of the ventral fin to the base of the anal fin, the distance from the cloaca to the base of the ventral fin, the distance from the cloaca to the base of the caudal fin, body height, head length, anal fin length, body thickness, head breadth, caudal peduncle length, head length behind the eye, and caudal peduncle height. Differences in tail fin length and snout length reached statistical significance (p ≤ 0.01); however, the difference in eye diameter was non-significant (p > 0.05).
The statistics of the standardized length traits of male and female G. eckloni are shown in Figure 3. The multivariate analysis of variance (MANOVA) revealed highly significant differences (p ≤ 0.001) were observed in the ratios of snout length to head length and caudal fin length to body length. Significant differences were observed in the ratio of head length behind the eye to head length (p ≤ 0.01) and the ratios of head width to head length and anal fin length to body length (p ≤ 0.05). However, differences in the remaining indices were not significant (p > 0.05).

3.2. Correlation Analysis Between Morphological Traits

Figure 4 demonstrates the correlation between the non-standardized and standardized morphological indices of G. eckloni. All non-standardized morphological indices exhibited positive correlations with each other. Specifically, the anal fin length, tail fin length, caudal peduncle length, and head length behind the eye exhibited weaker correlations with other indices. The correlations between the standardized indices were weaker, with both negative and positive correlations being observed. In particular, strong positive correlations were found between the ratio of anal fin length to body length and the ratio of post-orbital head length to head length, between the ratio of tail fin length to body length and the ratio of snout length to head length, and between the ratio of caudal peduncle length to body length and the ratio of eye diameter to head length. The ratio of head length to body length exhibited a stronger negative correlation with other standardized indices. In addition, the ratios of overall length to body length, snout length to head length, and caudal fin length to body length showed negative correlations with non-standardized traits.

3.3. Principal Component Analysis of the Morphological Traits of G. eckloni

The 26 morphological traits that were significantly different between male and female G. eckloni and significantly different after treatments of standardized were subjected to principal component analysis using a correlation matrix. The results are shown in Figure 5 and the Supplementary Materials. Five principal components with eigenvalues greater than 1 were extracted. The first principal component accounted for 50.688% of the variance, with substantial loading mainly on body length, fork length, overall length, body weight, and the distance from the cloacal aperture to the base of the pectoral fin. The second principal component accounted for 14.18% of the variance, with significant loading primarily on the ratios of head length behind the eye to head length, snout length to head length, and anal fin length to body length. The third principal component accounted for 7.943% of the variance, with predominant loading on the ratio of head length to body length. The fourth and fifth principal components accounted for 6.566% and 4.258% of the variance, respectively, resulting in a cumulative contribution rate of 83.635%.

3.4. Discriminant Analysis

A stepwise discriminant analysis was performed on the morphological traits that exhibited significant differences between male and female G. eckloni both before and after standardization. In this analysis, uncorrelated variables were progressively eliminated based on their contributions to the model. Eventually, two variables were selected, namely, body length (X3) and the ratio of head width to head length (X23). The equations established for discriminating between male and female G. eckloni are as follows:
Male: Y1 = 8.24 × X3 + 912.236 × X23 − 543.542
Female: Y2 = 8.917 × X3 + 931.182 × X23 − 582.314
A frequency distribution graph was plotted by calculating the discriminant scores for male and female G. eckloni (Figure 6). Using the discriminant analysis equation to enter the X3 and X23 values of 100 G. eckloni (48 males and 52 females) used to validate the discriminant equation, Y1 and Y2, respectively, were calculated. If Y1 was greater than Y2, the individual was classified as male; otherwise, it was classified as female. After retrospective validation of the sex of all individuals (Table 2), the actual discrimination rates for male and female individuals were 79.17% and 75.00%, respectively. The overall accuracy rate of the discriminant equation was 77.00%.

3.5. Hierarchical Cluster Analysis

The 26 morphological traits that exhibited significant differences between male and female G. eckloni both before and after standardization were subjected to hierarchical cluster analysis using Ward’s method. As shown in Figure 7a, the optimal clustering of the 166 individuals into three categories was determined through k-means analysis. The results are depicted in Figure 7b. The first category comprised 115 individuals, with female (76/115) and male (39/115) fish representing 66.1% and 33.9% of the total population in this category, respectively. The second category comprised 45 individuals, with male (38/45) and female (7/45) fish accounting for 84.4% and 15.6% of the total population in this category. The third category comprised six individuals, all of whom were male. Therefore, systematic cluster analysis efficiently classified all G. eckloni individuals into male and female groups.

3.6. Relationship Between Body Length and Body Weight in G. eckloni

Male G. eckloni had a body length ranging from 26.58 to 34.79 cm and a body weight ranging from 277.5 to 841.8 g, whereas female fish had a body length ranging from 27.35 to 36.71 cm and body weight ranging from 341.2 to 1070.0 g. Regression equations were fitted to the body length and body weight data of both male and female G. eckloni, resulting in the following equations:
Female :   BW = 0.0645 × S L 2 . 6134 ( R 2 = 0.7484 ,   n = 83 )
Male :   BW = 0 . 0192 × S L 2 . 9600 ( R 2 = 0.6772 ,   n = 83 )

4. Discussion

During the growth of fish as well as other animals, male and female populations tend to undergo significant changes in the morphological and physiological aspects of some organs and exhibit differences in growth, as early development is influenced by a combination of genetic and environmental factors [61,62]. Factors such as feeding and digestion, growth and reproductive energy allocation, and species-specific genetics contribute to sex-based differences in the growth of animals. According to the characteristics of energy distribution within animals, energy is primarily used for either growth or reproduction, not for both simultaneously. When food is abundant, fish reduce energy expenditure in processes other than growth during the breeding season, prioritizing the allocation of energy for gonadal development [63]. However, when food is scarce, an inhibitory competitive effect exists between weight gain and reproductive growth in fish, leading to a marked decrease in growth rate after sexual maturation [63]. Male G. eckloni typically reach sexual maturity at the age of 3 years, with a body length of over 25 cm, whereas their female counterparts usually attain sexual maturity at the age of 4 years, with a body length of usually over 30 cm. After reaching sexual maturity, fish prioritize energy for gonadal development, resulting in a significant decrease in the growth rate in male and female fish after 3 and 4 years, respectively. Consequently, female fish are usually larger than male fish after sexual maturity. In this study, the average body weights of male and female G. eckloni were 452.30 g and 594.77 g, respectively, aged 6–7 years. This result is consistent with the biological characteristics of G. eckloni and with the findings reported in other fish species, such as Larimichthys crocea [48], Scatophagus argus [49], Erythroculter ilishaeformis [50], Cyprinus carpio var. [64], Eleotris oxycephala [65], and Gymnocypris chilianensis [66].
Hierarchical cluster analysis of the morphological traits that were significantly different between male and female G. eckloni both before and after standardization showed that the sex of G. eckloni could be identified to a certain extent based on their morphological traits. Principal component analysis revealed five principal components that accounted for a cumulative contribution rate of 83.64%. The first principal component, with a contribution rate of 50.69%, was highly dependent on traits such as body length, fork length, overall length, weight, and the distance from the cloacal aperture to the base of the pectoral fin, explaining the overall morphological differences between male and female G. eckloni. The second, third, fourth, and fifth components explained the localized morphological differences between male and female G. eckloni. Stepwise discriminant analysis showed that the most significant differences were observed in body length and the ratio of head width to head length. The results of PCA, cluster analysis, and discriminant analysis suggested that the morphological differences between male and female G. eckloni were concentrated in body size and head morphology. Specifically, male G. eckloni had shorter body lengths, smaller body sizes, more pointed heads, and a smaller ratio of head width to head length. These differences may be related to not only the genetic and developmental mechanisms of G. eckloni [67,68,69,70] but also the sexual selection and ecological adaptations of this fish species [71]. Specifically, the head of male fish adapted a sharper or more exaggerated shape to gain an advantage in attracting female fish or in fighting. Different ecological niches and foraging strategies may also contribute to male and female fish displaying different morphological features of the head when adapting to environmental stresses [71,72,73]. Similar findings have been reported in studies on Larimichthys crocea [48], Erythroculter ilishaeformis [50], and Odontobutis potamophila [52].
After the two morphological indices used to establish the discriminant equation were incorporated into the equation for testing, the results demonstrated an overall predictive accuracy of 77.00% for G. eckloni, with an accuracy of 79.17% for male fish and 75.00% for female fish. Therefore, the discriminant equation established in this study can effectively determine the sex of G. eckloni. However, the morphological characteristics of each fish are influenced by their genetic information, environment, reproductive status, and bait resources [65,74,75,76], which may lead to morphological differences among fish. Consequently, further research is warranted to verify whether the discriminant equation applies to G. eckloni of different ages growing in other water bodies or different growth environments. Additionally, the method of identifying the sex of G. eckloni through morphological differences can be further improved by combining image recognition and sex marking [77].
In this study, another equation was established to describe the relationship between body length and body weight in G. eckloni. In this equation, the conditioning factor “a” represents the adaptability of G. eckloni to its environment. A higher “a” value indicates a more suitable environment for the survival of G. eckloni. In this study, the “a” values for male and female G. eckloni were 0.0192 and 0.0645, respectively. These findings suggest that the aquaculture environment from which the G. eckloni were collected is more suitable for the survival of female fish. In artificial breeding, the egg production capability of female fish determines the success of the breeding, leading breeders to adjust the environment to favor conditions more suitable for the growth of female fish. The “b” value in the equation is an important indicator of the synchrony of body length and weight growth in G. eckloni. The fish exhibit isometric growth when the “b” value equals 3. However, when it is less than 3, the fish exhibit negative allometric growth; that is, the increase in body length is greater than that in body weight. The smaller the “b” value, the greater this discrepancy. The fish exhibit positive allometric growth when the “b” value is greater than 3. In this study, the “b” value for male G. eckloni was 2.9600, indicating isometric growth, whereas that for female fish was 2.6134, indicating negative allometric growth. These findings indicated that female fish had a more significant conditioning factor than male fish, which is consistent with the biological characteristics of G. eckloni. By combining these biological characteristics with the established discriminant equation, the sex of G. eckloni can be identified based on its body shape. Specifically, male fish are characterized by a more elongated body and a more pointed head, which is of great significance when applied to large-scale fish breeding.

5. Conclusions

This study primarily employed morphometric methods to analyze and identify morphological differences between male and female individuals of G. eckloni. The results indicated that the primary morphological differences between male and female individuals of G. eckloni are concentrated in body size and head morphology, specifically that male G. eckloni are shorter in body length, smaller in body size, have a pointed head, and a smaller ratio of head width to head length. Additionally, the constructed model was validated by using a second batch of 100 G. eckloni individuals, achieving an accuracy rate of 77.00%. This indicates that geometric morphometric analysis is a feasible method for sex identification in G. eckloni. However, since the G. eckloni in this study came from a single source, whether the constructed model is applicable for sex determination in other populations of G. eckloni remains to be further investigated.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/fishes10080399/s1, Table S1: Eigenvalues and contribution rates in principal component analysis of morphological indicators of G. eckloni.; Table S2: Factor loadings in principal component analysis of morphological indicators of G. eckloni.

Author Contributions

Conceptualization, C.Z.; methodology, Q.W. and S.F.; software, Q.W., S.F. and X.C.; validation, C.Z.; formal analysis, Q.W. and S.F.; investigation, S.F., Y.D. and L.L.; resources, C.Z.; data reduction, Y.D. and L.L.; writing—original draft preparation, Q.W., S.F. and Y.F.; writing—review and editing, Q.W., S.F. and X.C.; project administration, C.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key R&D Program of China (2024YFD1200703); the National Natural Science Foundation of China (32160864); the Special Fund for Youth team of the Southwest University (SWU-XJPY202302); the Natural Science Foundation of Chongqing Province of China (CSTB2022NSCQ-MSX0566).

Institutional Review Board Statement

This study was reviewed and approved by Southwest University’s animal research protocols and conducted in accordance with the guidelines established by the Institutional Animal Care and Use Committee of Southwest University with the approval number: IACUC-20220415-16, dated: 15 April 2022.

Data Availability Statement

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request. The authors confirm that the data supporting the findings of this study are available within the article.

Acknowledgments

We sincerely thank Zeren Luowu for his assistance in field sampling, and Xiying Chen for language editing support. We are also deeply grateful to the journal editors and reviewers for their invaluable contributions to improving this manuscript through rigorous critique and constructive suggestions.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Schematic diagram of the measurement of various morphological characteristics of Gymnocypris eckloni (AI represents overall length, AH represents fork length, AG represents body length, DE represents trunk length, ON represents the distance from the cloacal aperture to the base of the pectoral fin, NR represents the distance from the base of the pectoral fin to the base of the ventral fin, PR represents the distance from the base of the ventral fin to the base of the anal fin, OR represents the distance from the cloaca to the base of the ventral fin, OS represents the distance from the cloaca to the base of the caudal fin, ML represents body height, PQ represents anal fin length, GI represents caudal fin length, FG represents caudal peduncle length, CD represents head length behind the eye, KJ represents caudal peduncle depth, AB represents snout length, BC represents eye diameter.).
Figure 1. Schematic diagram of the measurement of various morphological characteristics of Gymnocypris eckloni (AI represents overall length, AH represents fork length, AG represents body length, DE represents trunk length, ON represents the distance from the cloacal aperture to the base of the pectoral fin, NR represents the distance from the base of the pectoral fin to the base of the ventral fin, PR represents the distance from the base of the ventral fin to the base of the anal fin, OR represents the distance from the cloaca to the base of the ventral fin, OS represents the distance from the cloaca to the base of the caudal fin, ML represents body height, PQ represents anal fin length, GI represents caudal fin length, FG represents caudal peduncle length, CD represents head length behind the eye, KJ represents caudal peduncle depth, AB represents snout length, BC represents eye diameter.).
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Figure 2. Statistics of the morphological traits of male and female Gymnocypris eckloni: ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
Figure 2. Statistics of the morphological traits of male and female Gymnocypris eckloni: ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
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Figure 3. Statistics of standardized morphological traits of male and female Gymnocypris eckloni: X21 represents the ratio of overall length to body length, X22 represents the ratio of fork length to body length, X23 represents the ratio of head width to head length, X24 represents the ratio of head length behind the eye to head length, X25 represents the ratio of snout length to head length, X26 represents the ratio of eye diameter to head length, X27 represents the ratio of trunk length to body length, X28 represents the ratio of the distance from the cloacal aperture to the base of the pectoral fin to body length, X29 represents the ratio of caudal peduncle height to body height, X30 represents the ratio of the distance from the pectoral fin to the pelvic fin base to body length, X31 represents the ratio of the distance from the pelvic fin base to the anal fin base to body length, X32 represents the ratio of the distance from the cloaca to the base of the ventral fin to body length, X33 represents the ratio of the distance from the cloaca to the base of the caudal fin to body length, X34 represents the ratio of body height to body length, X35 represents the ratio of head length to body length, X36 represents the ratio of anal fin length to body length, X37 represents the ratio of caudal fin length to body length, X38 represents the ratio of body width to body length, and X39 represents the ratio of caudal peduncle length to body length; the same below; * indicates that p ≤ 0.05 which has statistically significant, ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
Figure 3. Statistics of standardized morphological traits of male and female Gymnocypris eckloni: X21 represents the ratio of overall length to body length, X22 represents the ratio of fork length to body length, X23 represents the ratio of head width to head length, X24 represents the ratio of head length behind the eye to head length, X25 represents the ratio of snout length to head length, X26 represents the ratio of eye diameter to head length, X27 represents the ratio of trunk length to body length, X28 represents the ratio of the distance from the cloacal aperture to the base of the pectoral fin to body length, X29 represents the ratio of caudal peduncle height to body height, X30 represents the ratio of the distance from the pectoral fin to the pelvic fin base to body length, X31 represents the ratio of the distance from the pelvic fin base to the anal fin base to body length, X32 represents the ratio of the distance from the cloaca to the base of the ventral fin to body length, X33 represents the ratio of the distance from the cloaca to the base of the caudal fin to body length, X34 represents the ratio of body height to body length, X35 represents the ratio of head length to body length, X36 represents the ratio of anal fin length to body length, X37 represents the ratio of caudal fin length to body length, X38 represents the ratio of body width to body length, and X39 represents the ratio of caudal peduncle length to body length; the same below; * indicates that p ≤ 0.05 which has statistically significant, ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
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Figure 4. Heatmap of the correlation between the non-standardized and standardized morphological indices of G. eckloni; * indicates that p ≤ 0.05 which has statistically significant, ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
Figure 4. Heatmap of the correlation between the non-standardized and standardized morphological indices of G. eckloni; * indicates that p ≤ 0.05 which has statistically significant, ** indicates that p ≤ 0.01 which has highly statistically significant, *** indicates that p ≤ 0.001 which has Extremely which has statistically significant.
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Figure 5. Principal component analysis of morphological indicators of G. eckloni; PC1 represents the first principal component and PC2 represents the second principal component.
Figure 5. Principal component analysis of morphological indicators of G. eckloni; PC1 represents the first principal component and PC2 represents the second principal component.
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Figure 6. Frequency distribution of discriminant scores for male and female Gymnocypris eckloni.
Figure 6. Frequency distribution of discriminant scores for male and female Gymnocypris eckloni.
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Figure 7. (a) K-means partitioning; (b) systematic cluster analysis of Gymnocypris eckloni.
Figure 7. (a) K-means partitioning; (b) systematic cluster analysis of Gymnocypris eckloni.
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Table 1. Statistics of the morphological traits of male and female Gymnocypris eckloni.
Table 1. Statistics of the morphological traits of male and female Gymnocypris eckloni.
TraitsMaleFemaleF-ValueDegrees of Freedomp-Value
Mean ± Standard DeviationMean ± Standard Deviation
X1 (AI, overall length, cm)34.60 ± 2.1037.56 ± 2.6065.2511.000.000
X2 (AH, fork length, cm)32.32 ± 2.0035.30 ± 2.4374.5221.000.000
X3 (AG, body length, cm)29.87 ± 1.8532.67 ± 2.2975.6751.000.000
X4 (DE, trunk length, cm)16.76 ± 1.3918.37 ± 1.4652.6531.000.000
X5 (ON, the distance from the cloacal aperture to the base of the pectoral fin, cm)16.60 ± 1.3918.30 ± 1.6651.131.000.000
X6 (NR, the distance from the base of the pectoral fin to the base of the ventral fin, cm)8.79 ± 0.719.72 ± 0.8757.7851.000.000
X7 (PR, the distance from the base of the ventral fin to the base of the anal fin, cm)8.48 ± 0.789.30 ± 0.8939.3261.000.000
X8 (SR, the distance from the cloaca to the base of the ventral fin, cm)8.03 ± 0.778.85 ± 0.9338.3971.000.000
X9 (OS, the distance from the cloaca to the base of the caudal fin, cm)7.36 ± 0.657.94 ± 0.6533.1381.000.000
X10 (LM, body height, cm)7.14 ± 0.697.66 ± 0.7621.4151.000.000
X11 (AD, head length, cm)6.48 ± 0.407.09 ± 0.5564.4781.000.000
X12 (PQ, anal fin length, cm)5.20 ± 0.605.50 ± 0.5910.8171.000.001
X13 (GI, caudal fin length, cm)5.08 ± 0.415.29 ± 0.459.1081.000.003
X14 (body thickness, cm)4.94 ± 0.495.34 ± 0.4332.5811.000.000
X15 (head breadth, cm)4.54 ± 0.435.00 ± 0.4150.5151.000.000
X16 (FG, caudal peduncle length, cm)4.40 ± 0.694.76 ± 0.5014.9731.000.000
X17 (CD, head length behind the eye, cm)4.02 ± 0.354.37 ± 0.5524.5241.000.000
X18 (JK, caudal peduncle depth, cm)2.44 ± 0.662.56 ± 0.232.4241.000.000
X19 (AB, snout length, cm)1.47 ± 0.161.64 ± 0.2626.3591.000.004
X20 (BC, eye diameter)1.20 ± 1.001.25 ± 0.760.1461.000.703
M (body weight, g)452.30 ± 104.27594.77 ± 131.7259.6911.000.000
Table 2. Identification of male and female Gymnocypris eckloni based on the discriminant equation.
Table 2. Identification of male and female Gymnocypris eckloni based on the discriminant equation.
SexSample NumberAccuracy of DiscriminationDiscrimination Classification
MaleFemale
Male4879.17%3810
Female5275.00%1339
Total10077.00%5149
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Wang, Q.; Fu, S.; Chen, X.; Duan, Y.; Lei, L.; Fan, Y.; Zhou, C. Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein. Fishes 2025, 10, 399. https://doi.org/10.3390/fishes10080399

AMA Style

Wang Q, Fu S, Chen X, Duan Y, Lei L, Fan Y, Zhou C. Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein. Fishes. 2025; 10(8):399. https://doi.org/10.3390/fishes10080399

Chicago/Turabian Style

Wang, Qiming, Suxing Fu, Xiaoyi Chen, Yuting Duan, Luo Lei, Yawen Fan, and Chaowei Zhou. 2025. "Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein" Fishes 10, no. 8: 399. https://doi.org/10.3390/fishes10080399

APA Style

Wang, Q., Fu, S., Chen, X., Duan, Y., Lei, L., Fan, Y., & Zhou, C. (2025). Analysis of Morphological Characteristics of Male and Female Gymnocypris eckloni Herzenstein. Fishes, 10(8), 399. https://doi.org/10.3390/fishes10080399

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