Effects of Croton sonderianus essential oil in tambaqui (Colossoma macropomum) feeds on growth, hematology, blood chemistry, and resistance of the fish to infection with Aeromonas hydrophila

This study aimed to assess the effect of essential oil from Croton sonderianus (EOCS) in diets for Amazonian fish tambaqui (Colossoma macropomum) (12.86 ± 0.34 g) before and after Aeromonas hydrophila infection. Five diets (348.20 g kg⁻¹ of crude protein) were prepared with graded levels of EOCS (35.12% of β–phellandrene) (0.0 (control), 0.25, 0.50, 1.00, and 1.50 mL kg diet⁻¹) and evaluated for 60 days, followed by 14 additional days of the bacterial challenge (0.2 mL of A. hydrophila solution at 1 × 10⁸ colony forming units mL⁻¹). Fish were fed until apparent satiation four times daily and maintained in 500-L tanks (n = 15 fish per tank; 5 tanks per treatment). Fish had no mortality. According to regression analysis, there was a proportional increase in the final weight, weight gain, specific growth rate, thermal growth coefficient, final length, hemoglobin, hematimetric indices, and liver glycogen levels before bacterial infection. In this same treatment (1.50 mL EOCS kg diet⁻¹), a decrease in the plasma total cholesterol, triglycerides, total protein, and albumin values was verified compared to other treatments. After bacterial infection, there was a positive linear effect for plasma triglycerides and albumin and liver total protein and glycogen levels and a negative linear effect for plasma glucose and aspartate aminotransferase levels with a dietary increase in EOCS. In conclusion, 1.50 mL EOCS kg diet⁻¹ is recommended for tambaqui juveniles because it improves growth performance, hematology, and biochemical parameters without compromising bacterial infection resistance.