Aquaculture xxx (xxxx) xxx Please cite this article as: S.R. Krupesha Sharma, Aquaculture, https://doi.org/10.1016/j.aquaculture.2020.736184 Available online 21 November 2020 0044-8486/© 2020 Elsevier B.V. All rights reserved. Evaluation of biosafety and tissue residue of oxytetracycline in juvenile snubnose pompano, Trachinotus blochii along with in vitro effcacy against fsh pathogens S.R. Krupesha Sharma a, * , T.G. Sumithra a , Suja Gangadharan a , Azhar Shahansha a , N.K. Sanil a , K. Ashok Kumar b , Prasanna Kumar Patil c a Fish Health Section, Marine Biotechnology Division, ICAR-Central Marine Fisheries Research Institute, Ernakulam North P.O., Kochi 682018, Kerala, India b Fish Processing Division, ICAR-Central Institute of Fisheries Technology, Matsyapuri P.O., Kochi 682 029, Kerala, India c Aquatic Animal Health and Environment Division, ICAR-Central Institute of Brackishwater Aquaculture, Raja Annamalai Puram, Chennai 600 028, Tamil Nadu, India A R T I C L E INFO Keywords: Oxytetracycline Snubnose pompano Histopathology Tissue residues, MIC MBC ABSTRACT Oxytetracycline (OTC) is a widely used antibiotic in both freshwater and marine intensive aquaculture practices. Responsible use of antibiotics requires data on in vitro effcacy against pathogens of targeted species, as well as on biosafety and tissue residue level in each targeted host. Accordingly, experiments were designed to evaluate the biosafety and tissue residue level of OTC in a marine aquaculture candidate species, viz., snubnose pompano (Trachinotus blochii). Biosafety of OTC was assessed by administration of medicated feed both at the therapeutic dose (80 mg/ kg biomass) and 3, 5, and 10 times the therapeutic dose. Exposure was done both for the rec- ommended duration of time (10 days) as well as two and three times higher than the recommended duration. Histological examination revealed moderate to severe tissue morphological changes in the liver, kidney, and gills of fsh exposed to OTC. The liver was the frst and most severely affected organ. Pathological effects in all the three selected organs were directly related to the dose and duration of OTC exposure. Further, tissue residue concentrations in the muscle of the group exposed to OTC at the therapeutic dosage for a duration of 10, 20, and 30-days were well below the maximum residual level prescribed by the European Commission and the US Food and Drug Administration, on day zero post-withdrawal, leaving its implications on consumer safety. Addition- ally, in vitro effcacy evaluation against marine fsh pathogens of the target species, viz., Vibrio harveyi, Vibrio vulnifcus, and Vibrio parahaemolyticus, showed that minimum inhibitory concentration and minimum bacteri- cidal concentration ranged from 0.6 to 1.5 μg mL 1 and 2.5 to >320 μg mL 1 , respectively. Altogether, the results will assist in the design and implementation of responsible use of OTC in aquaculture practices of T. blochii. 1. Introduction Aquaculture, the fastest-growing food-production industry in the world is plagued by outbreaks of various infectious diseases, posing a severe threat to the economy and sustainability of the sector (Pridgeon and Klesius, 2012). Among the varied infectious agents, bacterial pathogens are the major impediments to aquaculture (Klesius and Pridgeon, 2011). Bacterial diseases are known to cause severe economic impact annually to sustainable aquaculture practices worldwide, espe- cially in tropical climate (Pridgeon and Klesius, 2012). As there are no specifc antibiotics designed exclusively for aquaculture, authorised products developed for terrestrial animals are currently approved for aquaculture in controlled culture conditions to combat bacterial dis- eases (FAO, 2005). Of the approved antibiotics, oxytetracycline (OTC) is the most frequently used one in aquaculture, especially in Asian coun- tries (Olatoye and Basiru, 2013). Responsible use of antibiotics is necessary to reduce the raising concerns about antimicrobial resistance and antibiotic residues. Such responsible use in each species requires information on in vitro anti- bacterial activity against pathogens of targeted species as well as data on biosafety and withdrawal period of the drug in each targeted host. These data are critical to minimise the adverse impact on each fsh species, * Corresponding author. E-mail address: krupesh.sharma@icar.gov.in (S.R. Krupesha Sharma). Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture https://doi.org/10.1016/j.aquaculture.2020.736184 Received 20 July 2020; Received in revised form 26 October 2020; Accepted 18 November 2020