It is now well-documented that the functional urea cycle, present in C. batrachus, plays an important role in facing the problem of ammonia toxicity under hyper-ammonia stress (Saha and Ratha, 1989, 1998; Saha and Das, 1999; Saha et al.,
1999). The present investigation demonstrates the role of ureogenesis, via the functional urea cycle, in this air-breathing, walking catfish in avoiding the in situ ammonia build-up when living in alkaline water (pH 10) and in helping maintain the acid–base balance.