A triplicate experiment was conducted to evaluate the supplementation of monosodium glutamate into the diet on physiological responses, growth performances, and feed efficiency of north African catfish Clarias gariepinus cul-tured in high ammonia environment. A hundred fish with an initial body weight of 11.9±0.3 g was rearing for 60 days without any water exchange in nine plastic tanks (1x1x1 m3) at experimental pond of Department of Aquaculture, Bogor Agricultural University. During rearing

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... riod, fish were fed on the diet supplemented with 0%, 0.87%, or 1.74 % of monosodium glutamate, two times a day at satiation. Result shows that the supplementation of monoso-dium glutamate in feed stimulates change in fish physiological responses such as lower Alanin Transaminase mono-sodium glutamate enzyme activity, lower blood ammonia, and higher intestinal glutamine. Feeding using monoso-dium glutamate-supplemented feed at three different doses results in the same growth rate. However, the highest feed efficiency of North African catfish was recorded in the treatment of feed supplemented with 0.87% monosodium glutamate. Thus, it can be inferred that the usage of monosodium glutamate may improve physiological response and feed efficiency but does not affect fish growth rate.