Available online at www.worldscientificnews.com ( Received 20 July 2021; Accepted 13 August 2021; Date of Publication 14 August 2021 ) WSN 160 (2021) 203-216 EISSN 2392-2192 The effect of induction of bacteria Bacillus subtilis in feed on the immune system of carp (Cyprinus carpio Linnaeus, 1758) Rachmawati R. Andieny*, Yuniar Mulyani, Emma Rochima, Roffi Grandiosa Faculty of Fisheries and Marine Sciences, University of Padjadjaran, Bandung – Sumedang KM. 21 Jatinangor 45363, Indonesia *E-mail address: andienyr20@gmail.com ABSTRACT The induction of bacteria Bacillus subtilis into carp feed to improve the immune system has been widely carried out, but no one has discussed the blood picture and the resulting gene expression. This study aims to determine the effect of the induction of bacteria Bacillus subtilis on carp feed to improve the immune system. The method used is the exploration method with 3 treatments, namely Treatment A (addition of bacteria Bacillus subtilis 10 ml/kg feed with a density of 10 8 CFU/mL), Treatment B (addition of Bacillus subtilis bacteria 20 ml/kg feed with a density of 10 8 CFU/mL), and Treatment C (Control). After rearing fish for 14 days, gene expression analysis was performed. RNA taken from the kidneys and liver of carp was extracted using the phenol-chloroform method. RNA isolates were amplified using the semi-quantitative RT-PCR method. Observation parameters in the form of fish hematology consisting of total white blood cells and total red blood cells, as well as water quality. The results showed that the highest increase in gene expression was in treatment A, namely, liver samples (AH) of 19.76% and kidney samples (AG) of 16.04% which was in line with an increase in white blood cells by 29% and an increase in red blood cells by 21%. Keywords: Carp, Bacillus subtilis, TLR 2, Immune System, Cyprinus carpio, Aeromonas hydrophila