The aim of the present investigation was to evaluate the effect of carvacrol, administered with feed, on growth, haematology and survival tambaqui, Colossoma macropomum, infected by Aeromonas hydrophila exposed to hypoxia. Carvacrol was incorporated into fish feed at the following concentrations: 0 (control), 10, 20 and 40 g.kg−1 for 60 days. Fish fed 10 g.kg−1 of carvacrol‐enriched diet had an increase in final weight (72.68 ± 1.63) and specific growth rate (1.89 ± 0.03) and a decrease in apparent feed conversion compared (1.65 ± 0.09) with the control group. In addition, the condition factor (2.03 ± 0.04) and weight gain (49.31 ± 1.54) were also improved in animals fed 10 g.kg−1with carvacrol. RBC count, MCV, mean MCHC, LG‐PAS+, thrombocytes and lymphocytes presented no differences between treatments; however, Ht (25.6 ± 1.20) and mean MCV (224.05 ± 9.64) of the animals fed the highest carvacrol level were lower than the control animals, suggesting microcytic anaemia. Increased monocytes (6.54 ± 1.07), neutrophils (9.14 ± 0.57) and phagocytic activity (32.77%) were recorded in animals fed 10 g.kg−1 with carvacrol, in relation to the control. Glucose, cholesterol and albumin presented no changes; however, lower triglyceride values were observed in animals fed 40 g.kg−1 carvacrol‐enriched diet. Animals fed 10 g.kg−1 of carvacrol had higher plasma protein (3.31 ± 0.05) and globulin (1.97 ± 0.06) concentrations and a higher survival rate when submitted to bacterial infection. Thus, carvacrol‐enriched diet improves C. macropomum growth, haemato‐immune system, metabolism and resistance to A. hydrophila infection.