Influence of environmental ammonia on the production of nitric oxide and expression of inducible nitric oxide synthase in the freshwater air-breathing catfish (Heteropneustes fossilis)

► High environmental ammonia caused more production and accumulation of NO in air-breathing catfish (Heteropneustes fossilis). ► Hyper-ammonia stress caused induction and zonal specific expression of iNOS enzyme protein, mRNA expression in different tissues. ► Activation of NFκB that resulted under hyper-ammonia stress was believed to be the cause of induction of iNOS gene.