environment. However, the intensive pond culture of
clarid catfish in Thailand often suffered from high
mortality, which was suspected as a result of poor
water quality, i.e., high ammonia concentration. The
tilapia production in open ponds was remarkably
greater in the treatment of higher catfish:tilapia ratio.
This was undoubtedly resulted from a greater amount
of food material, i.e., phytoplankton, generated from
catfish wastes. However, the higher catfish stocking
density resulted in lower tilapia survival, which was
probably caused by deterioration of water quality
due to excessive amount of wastes, particularly the
relatively high NH3-N (>2 mgll) and extremely low
morning DO (