Physiological and growth responses of tambaqui (Colossoma macropomum) fed Croton conduplicatus essential oil and challenged with Aeromonas hydrophila

This study aimed to assess the effect of Croton conduplicatus essential oil (CCEO) in diets for tambaqui (Colossoma macropomum) (14.50 ± 0.07 g), a native Amazonian fish. Five diets (29.25% digestible protein; 3063.14 kcal digestible energy) were prepared: 0.00 (control), 0.25, 0.50, 1.00, and 1.50 mL CCEO kg diet^–1 and evaluated for 60 days, followed by 14 additional days of bacterial infection with Aeromonas hydrophila. Fish were fed until apparent satiation four times daily and maintained in 1,000-L tanks (n = 15 fish per tank; 5 tanks per treatment; randomized design) in a recirculatory aquaculture system. The main chemical compounds of CCEO were the monoterpenes 1,8-Cineole (20.72%), p-Cymene (12.45%), and α-Phellandrene (11.46%). Animals had no mortality, even after the bacterial infection, and CCEO did not influence the number of lesions in infected fish. According to quadratic regression analysis, feeding fish diets containing 0.85 mL CCEO kg⁻¹ increased their growth parameters and feed intake. The feed conversion ratio was reduced with 0.25 mL CCEO kg diet^–1. Before infection, the regression showed that the 1.00 mL CCEO kg diet^–1 reduced erythrocytes and increased hemoglobin, hematimetric indices, plasma glucose, total cholesterol, albumin levels, and plasma and liver alanine aminotransferase (ALT) activities. After bacterial infection, quadratic regression analysis showed that the control group had the highest plasma glucose and albumin values, and the treatment 0.50 mL CCEO kg diet⁻¹ increased mean corpuscular volume values and decreased plasma ALT activity. In conclusion, 0.85 mL CCEO kg diet^–1 is recommended for tambaqui because it can potentially improve growth performance and hemato-biochemical responses; however, CCEO did not influence responses against aeromoniasis.