LAUSR

Abstract There are indications that S-(+)-linalool is a viable anesthetic for use in aquaculture, but to date there is little scientific data on its pharmacokinetic profile. Therefore, we determined S-(+)-linalool distribution and depletion in tissues of silver catfish (Rhamdia quelen). Fish were submitted to an immersion bath with S-(+)-linalool (153 mg/L) for up to 30 min; afterwards, were transferred to anesthetic-free aquaria for recovery. Tissues (kidney, liver, muscle and gills) were collected 0.03, 0.5, 1, 1.5, 2, 4, 8, 12 and 24 h after onset of S-(+)-linalool exposure. Another group of fish was transferred to individual aquaria after anesthesia for recovery for up to 48 h to determine the excretion rate. Water samples were collected after 0.5, 1, 2, 6, 24 and 48 h of recovery; after each collection, the water was renewed. S-(+)-Linalool could be quantified in all tissue samples up to 12 h and in water up to 24 h. The presence of volatile metabolites in concentrations detectable by the method used was not verified in any of the samples. The maximum concentration (Cmax) was higher in the kidney, followed by liver, gills and muscle (143.15, 110.03, 54.49 and 20.76 μg/g, respectively), at 0.5 h (Tmax). Non-compartmental analysis revealed that S-(+)-linalool elimination is faster in the liver, followed by kidney, gills and muscle according to elimination constant (Kel: 0.20, 0.10, 0.07 and 0.06 /h, respectively) and terminal half-life (T1/2β: 3.45, 6.30, 9.96 and 11.04 h, respectively). The estimated areas under the curve from zero to 12 h (AUC0–t) and to infinity (AUC0–∞) were: 304.7 and 382.7 μg/g h (kidney), 228.23 and 242.76 μg/g h (liver), 130.03 and 207.58 μg/g h (gills), and 54.38 and 93.49 μg/g h (muscle), respectively. Around 68% of S-(+)-linalool was excreted in the first 2 h of recovery. Excretion rates after 0.5, 1, 2, 6 and 24 h of recovery were 85.10 ± 9.83, 52.45 ± 5.01, 22.67 ± 2.10, 5.62 ± 0.55 and 1.63 ± 0.05 mg/kg h, respectively. In general, silver catfish had no difficulty in eliminating S-(+)-linalool. Although elimination of S-(+)-linalool from the muscle is slower than from other tissues, it is not a limiting factor for its use, since the residual concentration in the muscle after 12 h is much lower than the accepted daily intake (500 μg/kg bw) recommended for this compound. Therefore, we recommend continuing studies with this phytochemical for possible approval as an anesthetic for aquaculture.