Assessment of patho-physiological responses, gill histopathology and SEM analysis in common carp (Cyprinus carpio) exposed to varied doses of chloramine-T: A potent chemotherapeutic agent

Chloramine-T (Cl-T) is a chemo-therapeutant used at aquafarms to control fish mortalities associated with bacterial and parasitic infections in freshwater aquaculture. It is also effective as a disinfectant against a wide range of viruses known to cause disease in fish. However, a very little information is available on the patho-physiological alterations in common carp (Cyprinus carpio) exposed to different doses of Cl-T. Herein, the present study aimed to assess the patho-physiological changes in common carp exposed to different doses of Cl-T (20 mg/L, 100 mg/L, and 200 mg/L) for 15 days followed by a post-exposure assessment for another 15 days. The results indicated a significant decrease in haematological indices viz., Total Erythrocyte Count (TEC), Total Leucocyte Count (TLC), Total Platelet Count (TPC), Haemoglobin (Hb), Haematocrit (Hct), and Mean Corpuscular Haemoglobin Concentration (MCHC) at higher Cl-T concentrations. Whereas, a decrease in some of the immune-biochemical parameters was also noted viz., lysozyme, NBT, Total Ig, phagocytic activity, protein, albumin and globulin in a dose-dependent manner. However, a significant increase in Mean Corpuscular Volume (MCV) and glucose levels was observed during exposure period. Histopathological analysis revealed gill hypertrophy, fusion of secondary lamellae, sloughing of lamellar epithelium and gill necrosis which were more pronounced with increasing concentration of Cl-T. The maximum damage to the gill was noted at a concentration of 200 mg/L. Whereas, scanning electron microscopic (SEM) analysis of gill revealed sloughing of lamellar epithelium, reduced interlamellar space and hypertrophy of secondary lamellae in Cl-T exposed fishes. Together, these results suggest that Cl-T exposure in common carp at 20 mg/L has a mild and acceptable effect on gill and physiology of fish, 100 mg/L has moderate effect, and 200 mg/L causes extensive damage to gills and physiology of fish. •Chloramine T (Cl-T) exposure at 20–200 mg/L was toxic to common carp.•Cl-T caused stress, anaemia, immunosuppression and histopathological gill lesions.•Cl-T-induced alterations were reversible and Cl-T at 20 mg/L can be considered safe.