Nanoformulations of Cymbopogon winterianus essential oil modulate anesthetic efficiency and antioxidant gene expression in Colossoma macropomum during transport

Transport stress represents a critical bottleneck in aquaculture, and conventional strategies to mitigate it often present limitations in efficacy or safety. This study evaluated the anesthetic efficacy of Cymbopogon winterianus essential oil (EOCW) and its nanoformulations (NE-EOCW and PCLN-EOCW), as well as their effect on the transcriptional response of antioxidant genes of tambaqui ( Colossoma macropomum ). A nanoemulsion (NE-EOCW) was prepared using Tween 80 and sonication, while poly-ε-caprolactone nanoparticles (PCLN-EOCW) were obtained by the solvent evaporation method. The EOCW was characterized by gas chromatography-mass spectrometry, while zeta potential, dynamic light scattering, and polydispersity index (PDI) analyses were conducted for NE-EOCW and PCLN-EOCW. In addition, the encapsulation effectiveness (EE) and loading capacity (LC) of PCLN-EOCW were evaluated. In Experiment 1, the induction and recovery times of 160 fingerlings exposed to EOCW, NE-EOCW, and PCLN-EOCW (25–150 mg L⁻¹) were evaluated. In Experiment 2, the transcriptional response of antioxidant enzymes ( cat and sod ) was evaluated by quantitative PCR in ninety-three tambaqui liver samples immediately after transport (IAT), 24, and 72 h after exposure to EOCW, NE-EOCW, PCLN-EOCW, and their respective controls (alcohol-free and alcohol-containing). Geraniol (28.79%), citronellal (24.33%), and citronellol (16.49%) were the main compounds identified in EOCW. NE-EOCW exhibited a consistent particle size (126–167 nm), colloidal stability (–25 and –37 mV), and PDI between 0.19 (day 3) and 0.06 (day 90), while PCLN-EOCW exhibited particle sizes between 194 and 208 nm and zeta potentials between –16.8 and –37.8 mV over 90 days, with PDI between 0.12 (day 3) and 0.16 (day 90), showing a decrease at day 15 (0.08), and an EE of 81.9% and an LC of 96.1%. Induction times for EOCW, NE-EOCW, and PCLN-EOCW ranged from 35 to 127 s, 37–404 s, and 33–388 s, respectively, while recovery times ranged from 167 to 287 s for EOCW, 127–255 s for NE-EOCW, and 143–285 s for PCLN-EOCW. Notably, NE-EOCW (10 mg L⁻¹) decreased cat and sod mRNA levels at 72 h of exposure during prolonged transport (24 h), whereas the alcohol-containing control increased transcript levels under the same conditions. In conclusion, these nanoformulations improve anesthetic efficiency and modulate transcriptional response to oxidative stress without compromising water quality, supporting their potential application as sustainable nanotechnological tools for tropical aquaculture.