Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres Triclosan induces immunosuppression and reduces survivability of striped catfish Pangasianodon hypophthalmus during the challenge to a fish pathogenic bacterium Edwardsiella tarda Kuntal Krishna Bera a , Saurav Kumar a,* , Tapas Paul a , Kurcheti Pani Prasad a , S.P. Shukla a , Kundan Kumar a a ICAR- Central Institute of Fisheries Education, Mumbai, 400 061, India ARTICLE INFO Keywords: Triclosan P. hypophthalmus Cellular Humoral Immunosuppression ABSTRACT Toxicological studies on the emergent pollutant, triclosan (TCS) have established the wide-ranging effects of the compound on fish and other aquatic organisms. Although the available literature describes the standalone effects of TCS on growth and metabolism of fish yet, reports about the combined effects of TCS with microbial pa- thogens are scarce. In a real environment, a combined exposure to TCS and pathogens is of common occurrence, therefore, such investigation facilitates in developing a better understanding about the gross effects of pollutants and microbial pathogens on aquatic organisms including fish. In this context, the experimental fish (striped catfish, Pangasianodon hypophthalmus) were exposed to three different concentrations of TCS viz. 10, 20 and 30% of 96 h LC 50 (1177 μgL -1 ) for 45 days including two control group firstly solvent control (without TCS) group and another one (without solvent and TCS) group in triplicate. Sampling was performed fortnightly and blood, serum and tissues (liver, and gills) samples were collected for evaluating immunological and biochemical parameters. Following 45 days of the experiments, the experimental fish in each treatment group including controls were challenged with a fish pathogenic bacterium Edwardsiella tarda (LD 50 dose) and fish mortality was daily monitored for calculating cumulative mortality till 7 days and further, relative per cent survivable was estimated. A significant reduction in cellular immune responses i.e. respiratory burst activity (RBA), myelo- peroxidase activity (MPO), phagocytic activity (PA) and humoral immune components viz. serum lysozyme activity, total immunoglobulin in serum, ceruloplasmin level, serum total protein, albumin and globulin level was evident in TCS exposed groups in comparison to control during the experimental periods. Further, oxidative stress parameters viz. superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferase (GST) activity in liver and gill tissue exhibited a dose-dependent increase in activity with related to TCS concentration during the experimental periods. A significant reduction in relative percentage survival was observed with increasing TCS concentration. The present study reveals that TCS can inhibit the cellular and humoral components of the innate immune system of the fish and can elevate the mortality due to TCS mediated immunosuppression in fish during the bacterial infection. 1. Introduction In an appreciable number of reports, the toxic effects of the emer- gent pollutants (EPs) have been testified for their vital adverse impacts on the physiology of aquatic organisms including fish. Among the EPs, triclosan (TCS) is of serious concern because of its use as a broad- spectrum antibacterial and antimicrobial agent in personal care pro- ducts (Orvos et al., 2002; Karmakar et al., 2019). In recent time the manifestation of TCS in the aquatic ecosystems is becoming a global concern due to their ubiquitous occurrence in concentrations ranging from 1.4 to 40,000 ng L -1 in surface waters of lakes, rivers and streams, and in the sea from 0.001 to 100 ng L -1 (Dhillon et al., 2015). TCS mainly discharged from Wastewater Treatment Plants (WWTPs) into the aquatic environment, due to their partial inability to remove it, with detected concentrations ranging from 10 to 2210 ng L -1 in European WWTP effluents (Bedoux et al., 2012). TCS usually showed as endocrine disrupter having high octanol-water Partition coefficient (log K ow 4.76) and high hydrophobicity leads to bioaccumulation potential (Dhillon et al., 2015). In India, Selvaraj et al. (2014) estimated the mean bioaccumulation factor (BAFw) of TCS in water and sediment of https://doi.org/10.1016/j.envres.2020.109575 Received 2 January 2020; Received in revised form 2 April 2020; Accepted 22 April 2020 * Corresponding author. Aquatic Environment and Health Management Division, ICAR- Central Institute of Fisheries Education, Mumbai, 400 061, India. E-mail addresses: sauravsinha535@gmail.com, saurav@cife.edu.in (S. Kumar). Environmental Research 186 (2020) 109575 Available online 27 April 2020 0013-9351/ © 2020 Elsevier Inc. All rights reserved. T