Seasonal Trends of Freshwater Gastropods in Relation to Physicochemical Variables in the Upper Brahmaputra Basin, Assam, India

Background: Limited scientific exploration and documentation have been conducted on the diversity, morphology, physiology, biochemical characteristics and nutritional value of gastropods in this region. The study attempts to present an outline of freshwater gastropods and highlight the significance of physicochemical variables in clarifying their distribution patterns in the upper Brahmaputra Basin of Assam. Methods: Nine physicochemical parameters were analyzed across 20 sampling stations in four seasons: Pre-monsoon, monsoon, post-monsoon and winter, over three consecutive years, from 2022 to 2024. The Quadrat sampling method (quadrat size-1m2) was followed by taking 10 random sampling sites in each sampling station for sampling across different stations. Diversity indices, principal component analysis (PCA), canonical correspondence analysis (CCA) and linear regression analysis were performed to explore the correlations between physicochemical parameters, sampling stations and freshwater gastropod assemblage. Result: A total of 16,124 gastropod samples were collected, representing 18 species from three orders-Archaetaenioglossa, Sorbeoconcha and Hygrophila-and six families-Viviparidae, Ampullaridae, Thiaridae, Pachychilidae, Lymnaeidae and Planorbidae. One-way ANOVA substantiated that multiple physicochemical parameters were considerably distinct and Pearson correlation coefficients showed mild to strong links with the distribution of gastropods. Strong positive correlations were found for pH (r = 0.55), DO (r = 0.64) and TA (r = 0.75), while chloride content showed a negative connection (r = -0.30). Principal component analysis (PCA) and canonical correspondence analysis (CCA) revealed that pH, DO, TDS, TA and TH all play important roles in influencing gastropod distribution.