International Journal of Life Sciences International Peer Reviewed Open Access Refereed Journal Int. J. of Life Sciences, 2020; 8 (1):93-101 ISSN:2320-7817(p) | 2320-964X(o) Original Article Open Access © 2020 |IJLSCI www.ijlsci.in | 93 Sensitivity of the freshwater tropical oligochaete, Branchiura sowerbyi (Beddard, 1892) to the grey list metal, Zinc Kishore Dhara 1* , Shubhajit Saha 2 , Asish Kumar Panigrahi 3 , Nimai Chandra Saha 4 1 Office of the Deputy Director of Fisheries, Government of West Bengal, 9A, Esplanade East, Kolkata 700 069, West Bengal, India 2 Assistant Professor, Department of Zoology, Sundarban Hazi Desarat College, South 24 Parganas, 743611, West Bengal, India 3 Department of Zoology, University of Kalyani, Nadia 741 235, West Bengal, India 4 Fisheries Ecotoxicology Research Laboratory (Vice-Chancellor’s Research Group), Department of Zoology, University of Burdwan, Golapbagh, Bardhhaman 713 104, West Bengal, India *corresponding author, e mail: kishordhara@gmail.com Manuscript details: ABSTRACT Received: 01.02.2020 Accepted: 09.03.2020 Published: 05.04.2020 Cite this article as: Kishore Dhara, Shubhajit Saha, Asish Kumar Panigrahi, Nimai Chandra Saha (2020) Sensitivity of the freshwater tropical oligochaete, Branchiura sowerbyi (Beddard, 1892) to the grey list metal, Zinc, Int. J. of. Life Sciences, Volume 8(1): 93-101. Copyright: © Author, This is an open access article under the terms of the Creative Commons Attribution-Non-Commercial - No Derives License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Available online on http://www.ijlsci.in ISSN: 2320-964X (Online) ISSN: 2320-7817 (Print) Although the freshwater oligochaete, Branchiura sowerbyi Beddard, 1892 (Oligochaeta: Naididae: Rhyacodrilinae) has been used as an indicator organism to monitor aquatic pollution, the data on the toxic effects of the grey list metal, zinc on this worm is remained scanty. The present study was undertaken to determine the sensitivity of the worm, B. sowerbyi to zinc on the basis of 24, 48, 72 and 96h lethal concentrations (LC1, 5, 10, 15, 50, 85, 90, 95, 99) and their behavioural responses. The 96h LC50 value of zinc with 95% confidence limit to the worm was recorded as 45.48 (41.32-49.33) mg/l. The rate of mortality of the worm was significantly increased (p<0.05) with increasing concentrations and time of exposure (24, 48, 72 and 96h). The study further focussed on estimation of the toxicity factor at different time scale and possible safe level of zinc to the worm to strengthen the base line data that could be used to set up local water quality criteria (WQC) for the toxicant. The worms showed behavioural changes like clumping tendency, movement and mucous secretion with increasing concentration of the toxicant and the progress of time. The findings can be used in determination of ecological risk assessment for the worm to zinc toxicity as well as to understand its mode of action in the light of their ethological changes. Key words: Zinc, Branchiura sowerbyi, acute toxicity, toxicity factor, safe level, behavioural responses INTRODUCTION The bottom dwelling tropical oligochaete, Branchiura sowerbyi Beddard, 1892 (Oligochaeta: Naididae: Rhyacodrilinae) is broadly distributed in the