Abstract. This study was conducted to determine the effect of guar gum-GG, heat-killed Lactobacillus plantarum L-137 (HK L-137) and phytase on the growth, digestibility, and immune response of bighead catfish (Clarias macrocephalus), in order to contribute to formulating effective and environmentally friendly feed for bighead catfish reared in recirculation aquaculture systems (RAS). The experiment consisted of five diet treatments with and without additives: T1 (Control-CT), T2 (CT supplemented with GG at 5 g kg-1), T3 (CT with GG at 5 g kg-1 and HKL 137 at 0.02 g kg-1), T4 (CT with GG and 0.15g phytase per kg of diet) and T5 (CT with GG, HKL 137 and phytase).
The feeding trial was carried out for 56 days and all treatments were performed in triplicate. The results showed that the survival rate of the fish was not affected by diets supplemented with either guar gum (at 5 g kg-1), phytase (0.15 g kg-1) or HK L-137 (0.02 g kg-1). Dietary guar gum (5 g kg-1) addition did not diminish performance or feed digestibility and it did not improve the fecal characteristics or immune response of bighead catfish. On the other hand, inclusion of both phytase and HKL 137 in the diet not only increased growth performance and feed digestibility, but also the fecal characteristics and the immune response of bighead catfish. Neither phytase nor HK L-137 had any effect on the fecal pellets size. A supplement of 5 g guar gum, 0.15g phytase and 0.02 g HK L-137 per kg of diet appears to be suitable for raising bighead catfish (Clarias macrocephalus) in RAS systems.