The aim of this study was to evaluate the resistance of Rhamdia quelen (silver catfish) to Aeromonas hydrophila infection after treatment with pure and nanoencapsulated forms either terpinen-4-ol, thymol, or carvacrol and the effects of these treatments on fish metabolic responses. After A. hydrophila inoculation, fish were treated with 30 min daily baths for 6 consecutive days with terpinen-4-ol, thymol, or carvacrol in their pure or nanoencapsulated forms at concentrations of 5, 10, 15 or 25 mg L-1. A positive control group, negative control group and saline group were also included. Survival was evaluated at the end of treatment for six consecutive days. Muscle and liver were collected to determine glucose and lactate levels. The fish treated with the nanoencapsulated form of the compounds had a high survival rate, similar to saline group and negative control groups. The carvacrol, thymol and terpinen-4-ol nanoencapsulated forms improved survival of silver catfish infected with A. hydrophila. Muscle and liver glucose and lactate levels are not indicated as biomarkers because they did not present any correlation between the metabolic state of the fish and the bacterial infection.