Effects of ammonia stress on food ingestion, growth, digestion and antioxidant capacity were investigated in juvenile yellow catfish Pelteobagrus fulvidraco (Richardson) with initial body weights of 20.24 +/- 0.18g. The fish were reared in triplicate in 15 experimental tanks at a rate of 30 fish per tank for 56days. Water was maintained at a dissolved oxygen (DO) level of over 6.2mgL(-1), pH 7.2-7.6, and temperature of 29.0 +/- 1.5 degrees C under a natural 12L: 12D photoperiod. Survival, food ingestion (FI), specific growth rate (SGR), food conversion efficiency (FCE), apparent digestibility coefficient (ADC), total antioxidant capacity (T-AOC), levels of glutathione (GSH) and malonaldehyde (MDA), and activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-PX) of the juveniles were determined in total ammonia nitrogen (NH3-N+NH4-N) levels of 0 (control group), 3.36, 6.72, 13.44 and 26.88mgL(-1). The results show that the survival, FI, SGR, FCE, and ADC decreased significantly with an increase in total ammonia nitrogen (p<.05), and a significantly negative correlation between SGR and total ammonia nitrogen levels (p<.05). T-AOC, SOD, CAT, GSH-PX and GSH in the blood, liver and gills were found to decline significantly with an increase in the total ammonia nitrogen level (p<.05), while the MDA in the blood, liver and gills was elevated significantly with the increase in total ammonia nitrogen (p<.05). The results indicate a threshold in the induction of the T-AOC and activities of antioxidant enzymes in yellow catfish tissues with a total ammonia nitrogen increase. In the present study the total ammonia nitrogen threshold thus changed from 6.72mgL(-1) in the juvenile yellow catfish.