Performance of Eucalyptus saligna essential oil growth in diets of Colossoma macropomum juveniles

Introduction: Plant-derived feed additives have emerged as sustainable alternatives to improve fish performance in aquaculture. This study evaluated the effects of dietary ethanolic extract of Eucalyptus saligna (EOES) on the growth performance of juvenile tambaqui (Colossoma macropomum) reared in a recirculating aquaculture system (RAS). Methods: A total of 480 juveniles (3.41 ± 0.30 g) were distributed into sixteen 180 -L tanks connected to an RAS. Four diets containing 0.0, 0.5, 1.0, or 2.0 g EOES kg^-1 feed were tested in a completely randomized design with four replicates per treatment. Fish were fed twice daily for 40 days. Weight (W), daily weight gain (DWG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), biomass, and survival were evaluated. Results: After 10 days, fish fed 0.5 g kg^-1 EOES showed higher W, DWG, SGR, and PER, and lower FCR than the control group (p < 0.05). After 20 days, EOES supplementation increased W (12.62–13.16 vs. 8.81 g), DWG (0.59–0.64 vs. 0.33 g day^-1), biomass (1.98–2.06 vs. 1.47 kg m^-3), and reduced FCR (1.09–1.18 vs. 1.79). Regression analysis estimated maximum W and feed consumption at 1.31 and 1.23 g EOES kg^-1 feed, respectively. After 30 days, fish fed EOES reached 22.08–22.35 g compared with 12.87 g in the control, while optimal inclusion levels ranged from 1.34 to 1.38 g kg^-1 feed. After 40 days, final weight reached 36.41 g at 1.0 g kg^-1 EOES versus 17.79 g in the control, with maximum W, DWG, and feed consumption estimated at 1.44, 1.63, and 1.68 g EOES kg^-1 feed, respectively. Conclusion: EOES improved growth performance and feed efficiency in juvenile tambaqui, with optimal dietary inclusion ranging from 1.3 to 1.7 g kg^-1 feed.