Table 3 and Table 4 shows the average values with standard deviation of TL,SL and 26 truss measurements analyzed for male and female populations respectively. The population of Jatanbari, Amarpur, Maharani, Kakraban and Sonamura were more or less similar in respect of mean size of total length and standard length for both sexes. One-way ANOVA test showed that incase of female 5 truss measurements out of 26 were found to be significantly (
p< 0.05) different among populations whereas none was statistically significant difference in male. All correlation coefficients were estimated to know the degree of association between the traits for both male and female populations (Table 8 and Table 9). The ANOVA (p<0.05) revealed the most effective truss morphometric variation on sexual dimorphism was found in Maharani population followed by Sonamura (Table 5). In case of male, the PCA based on 26 truss measurements retained two components according to PA, explaining 91.01 % of the total variance. The first (PC1) and second (PC2) principal components accounted for 78.22 and 12.79 of the total variance, respectively (Table 6 and Fig 3). Thus, PC1 was the most important component contributing to separation among populations. These differences were primarily because of the strong loading of 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 1-12, 2-11, 2-12, 2-13, 3-11, 3-13, 4-13, 5-11, 5-12, 6-10, 6-11, 11-13 and 12-13 characters.Almost 50% of these characters were involved in longitudinal body shape changes
i.e. shape changes corresponding to the anterior-posterior body that reflect length changes. Strong loading of characters involved in body depth shape variation was also observed (Table 6). In the case of PC2, within the two characters that exhibited strong loadings, most were associated to body depth shape variation.
On the other hand in female, the PCA based on 26 truss measurements retained two components according to PA, explaining 98.08 % of the total variance. The first (PC1) and second (PC2) principal components accounted for 76.26 and 21.82 of the total variance, respectively (Table 7 and Fig 3). Thus, PC1 was the most important component contributing to separation among populations. These differences were primarily because of the strong loading of 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 1-12, 2-11, 2-12, 2-13, 3-13, 4-13, 5-11, 5-12, 6-11, 11-13 and 12-13 characters. Most of these characters were involved in longitudinal body shape changes i,e. shape changes corresponding to the anterior-posterior body that reflect length changes. Strong loading of characters involved in body depth shape variation was also observed (Table 7). In the case of PC2, within the four characters that exhibited strong loadings, most were associated to body depth shape variation.
Visual examination of plots of PC1 and PC2 scores revealed that the truss measurements were highly overlapped in male specimens among populations in compare with female populations (Fig 4 and 6). Also, plots of PC1 and PC2 scores revealed that morphological measurements in male were closely related among population of Jatanbari, Kakraban, Amarpur, Maharani and in females Jatanbari, Amarpur and Kakraban populations (Fig 5, 6). The location wise scatter plot of PC1 and PC2 separated the Sonamura population from other populations in both sexes. A high degree of morphological homogeneity was observed between Amarpur and Maharani population in males (Fig 8) and Jatanbari and Amarpur populations in females (Fig 9).
In case of male, the dendrogram derived from cluster analysis revealed the clear isolation of Sonamura population from other populations. In this analysis, the five populations resulted in two main distinct groups: the first group comprised only Sonamura population, while the second group included Maharani, Amarpur, Kakraban and Jatanbari populations. The strong morphometric similarity was observed between the populations of
Sperata seenghala from Amarpur and Maharani when compared to other populations. On the other hand, in case of female populations, the dendrogram derived from cluster analysis revealed the distinct isolation of Sonamura population from other populations. In this analysis, the five populations resulted in two main groups: the first group comprised only Sonamura population, while the second group included Amarpur, Jatanbari, Kakraban and Maharani population. The strong morphometric similarity was observed between the populations from Jatanbari and Amarpur when compared to other populations (Fig 7).
The results of the present study revealed that
S.seenghala from different study area in the River Gomati of Tripura exhibited morphometric variability forming two morphological types in both sexes: Sonamura population was separated as one group from the Jatanbari, Amarpur, Maharani and Kakraban populations, which together formed a separate group. Generally, teleost fishes show a greater degree of disparity within and between populations when compared to other vertebrates and are more prone to morphological variation induced by different environmental factors such as temperature, habitat condition, pH
etc. (
Wimberger, 1992). Our study results clearly demonstrate that there is significant phenotypic variation among the five studied populations, also between the sexes.
The scatterplot analysis of first two principal components of both male and female populations led to the identification of two phenotypically distinct local populations. The result derived from the PCA analysis in the study was further confirmed by the cluster analysis based on Euclidian square distance, which demonstrated that, among the five populations, four showed closely related and remaining one was clearly distinct.The intermingling relationship was highest in Amarpur and Maharani regions in males and Jatanbari and Amarpur regions in females which may be attributed to the similar geographical positions and climatic conditions of the study areas. The finding of the present study indicated that the population differentiation which resulted from different multivariate analyses in females was higher than in males. In the present study, the size effect had been removed successfully by allometric transformation and the significant differences between the populations are due to body shape variation when tested using ANOVA. Most of the morphometric measurements with strong loading irrespective of sex are related with longitudinal body shape changes i,e. shape changes corresponding to the anterior-posterior body that reflect length changes.
Our results are similar to those of
Hamed and Hosein (2013);
Mohaddasi et al. (2013);
Vatandoust et al., (2015); Hanif et al. (2019);
Muslimin et al. (2020). Understanding the origin of morphological differences between populations of
S.seenghala is challenging because of fish morphology is a complex phenotype that is determined by genetics and environmental factors and the interaction between them. The different sampling stations are geographically isolated and might be environmental and water quality fluctuations in different sampling stations. This is why the dendrogram formed two clusters (Fig 7). The similar result has reported by
Mahfuj et al. (2017) and
Ethin et al. (2019).
Truss network measurements are a series of distances calculated between landmarks that form a regular pattern of connected quadrilaterals or cells across the body form that enhance discrimination between group, based on a systematic detection of body shape differences (
Strauss and Bookstein, 1982;
Rawat et al., 2017). This type of morphometric analysis has not yet explored in
S.seenghala, in spite of its potential to facilitate interpretation of morphological variation through multivariate analysis, such as PCA. In our case, the truss-based system showed a high performance to distinguish
S.seenghala populations based on morphological data and also to determine the specific body shape characters that contributed to such variations.