Otolith morphological variations reveal intraspecific diversity in two-spot barb, Pethia ticto (Hamilton, 1822), inhabiting the riverine ecosystem

The intraspecific variation in otolith wavelet coefficients, contours, and morphometric variables (six size and nine shape indices) was analyzed to discriminate stock variation in Pethia ticto collected from four selected sites along the River Ganga (Narora, Kanpur, Varanasi, and Bhagalpur). The wavelet coefficients extracted revealed symmetrical yet site-specific contour variations, particularly along the rostral, dorsal, and posterior margins, with the fourth-level wavelet explaining 98% of the cumulative accuracy and being selected for contour analysis. Permutational analysis of multivariate dispersion (PERMDISP) (F = 6.11, p = 0.002) and permutational multivariate analysis of variance (PERMANOVA) (F = 8.42, R2 = 0.179, p = 0.001) confirmed significant intraspecific variation among sites, indicating spatial heterogeneity in otolith morphology. Canonical analysis of principal coordinates based on wavelet coefficients distinctly segregated the four populations, accounting for 86% of the total variation across the two canonical axes. Nonparametric tests (Kruskal–Wallis and post hoc Dunn’s tests) indicated significant intersite variation (p < 0.001) in major otolith size and shape indices. Random forest achieved 78.33% and 72.5% and gradient boosting classifiers achieved 70.83% and 71.67% classification accuracies, respectively, when applied to wavelet coefficients and otolith morphometric variables. These observations reveal considerable population structuring, highlighting the significance of otolith shape and morphometric variables as robust markers for distinguishing the stock of P. ticto along the River Ganga and their potential application in site-specific fisheries management and conservation.