A New article on how we can use phytoplankton and fish diets as bioindicators of river health in Narayani and East Rapti Rivers of Nepal has been published, led by Aakriti Adhikari and co-authored by Rabin Sharma and Chhatra Mani Sharma. The article has been published in the Aquatic Ecology journal and can be accessed via https://doi.org/10.1007/s10452-025-10254-2. The full text can be available from the authors (if not accessible online).
Citation: Adhikari, A., Sharma, R., & Sharma, C.M. Phytoplankton and fish diet as bioindicators of river health in the Narayani and East Rapti rivers, Nepal. Aquatic Ecology, 60, 14 (2026). https://doi.org/10.1007/s10452-025-10254-2
Abstract:
Biological indicators, such as phytoplankton, are crucial in monitoring changes in freshwater ecosystems as these are directly affected by nutrient concentration which helps to regulate their growth and development. Phytoplankton can serve as a biomonitoring tool because the phytoplanktonic species present in the diet can be used as bioindicator. This study aims to evaluate the use of phytoplankton and fish diet as bioindicators of river health in two important rivers, Narayani and East Rapti, of Nepal. The impact of water quality on phytoplankton, both in habitat and in the fish diet, was also assessed. Phytoplankton, fish gut and water samples were collected from 27 sites including the main river and its major tributaries. The correlational analysis and multiple linear regression determined the relationship between physico-chemical parameters and phytoplanktonic species in habitat. Twenty-one phytoplanktonic species were recorded from different habitats and 25 species from the fish diet. Spirogyra sp. was the dominant taxa in both habitat and the fish diet. Whereas Ulothrix sp. was the second most preferred food item for fish. Varied food items were recorded in Channa punctata, Pethia conchonius, Opsarius bendelisis and Acanthocobitis botia and limited food items were recorded in Chitala chitala, Garra annandalei, Puntius terio, Cabdio jaya, Tor mosal, Pseudambassis baculis, Botia lohachata, Botia histrionica, Salmostoma acinaces, Bangana dero, Botia geto, Aorichthys seenghala, and Anabas cobojius. Phytoplankton in habitat was positively related with temperature, EC, TDS, chloride, alkalinity, total hardness, calcium hardness, magnesium hardness, free CO2, NO3−, K+, Ca2+, Mg2+, and Na+ had negative relationship with DO, pH, PO43−, and NH3. Sites with dense settlement and industrialized areas had more pollutant tolerant phytoplanktonic species both in habitat and fish diet which indicates an influence of pollution in aquatic biota. Temporal monitoring of aquatic biota is recommended to track changes in river health of both Narayani and East Rapti rivers.
