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¹ ICAR-Directorate of Coldwater Fisheries Research, Bhimtal, Uttarakhand-263136, India DOI : 10.4194/TRJFAS25510 Viewed : 103 - Downloaded : 93 Saprolegnia is a genus of oomycetes which comprises important pathogens of salmon and trout species. There is re-emergence of Saprolegnia in the vulnerable fish species due to lack of effective agents against the microbes. Here, we report the isolation of Saprolegnia species from rainbow trout (Oncorhynchus mykiss) and its identification as S. parasitica and S. australis based on the nucleotide sequences of the internal transcribed spacer region. The isolates were used for evaluation of the anti-oomycete activity of chloramine T (CA-T), a commonly used drug against bacterial gill disease. In molecular docking, CA-T was found to interact with key proteins, host targeting protein, TKL protein kinase, and plasma membrane ATPase of Saprolegnia through hydrogen bond and hydrophobic interactions, which indicates the probable activity against the organism. In vitro experiments revealed that 400 mg/L of CA-T can kill S. parasitica, whereas a higher concentration of 600 mg/L was required to produce the similar effect in S. australis. The results indicate that CA-T is effective against Saprolegnia, but susceptibility is variable amongst different species. Overall, the findings highlight the anti-Saprolegnia activity of CA-T and the importance of correct identification of the causative agent to decide the optimum dose for judicious use of drug. Keywords : Molecular identification Internal transcribed spacer In silico analysis Minimum inhibitory concentration Minimum oomyceticidal concentration