Limnological Analysis with Main Emphasis on the Influence of Physico-Chemical Parameters on Phytoplankton and Fish Faunal Diversity Distributional Pattern in Beru Stream, Mandi District, Himachal Pradesh (India)

the current investigation entails a comprehensive assessment of the limnobiological conditions within Beru stream, located in the Mandi district of Himachal Pradesh. It examines both abiotic and biotic aspects, focusing on phytoplankton and fish diversity. Six phytoplankton genera were identified, falling under <i>Bacillariophyceae</i> and <i>Chlorophyceae</i> classes. Concurrently, 5 fish species were documented, belonging to the <i>Cyprininae, Danioninae</i> and <i>Sisorinae</i> subfamilies. Furthermore, our research involved the analysis of various abiotic parameters, including air and water temperature, pH, electrical conductivity, total dissolved solids, alkalinity, dissolved oxygen, total hardness, Ca<sup>2+</sup> and Mg<sup>2+</sup> hardness, chloride concentrations, as well as phosphate and nitrate levels. These abiotic parameters were correlated with both phytoplankton and fish population size. The study also undertook a statistical examination of the relationship between phytoplankton and fish population sizes. In order to evaluate the diversity within the stream, several diversity indices, including Simpson's index, Simpson's index of diversity, Shannon index of diversity, Pielou's index of evenness and Sorenson similarity index were employed. The calculated values of the water quality index (WQI) were found to fall within the range of 33.91 to 59.16. These values suggest that the water quality within Beru stream spans a spectrum from "good" to "poor" according to the WQI classification. Notably, it was observed that the presence of excessive nutrient levels, particularly phosphates and nitrates, could lead to the heightened presence of a diverse array of flora and fauna during the month of March. Consequently, based on the WQI assessment, March was documented as a period characterized by poor water quality.