Persistence of residues of malachite green in juvenile eels ( Anguilla anguilla)

The depletion of malachite green (MG) and leuco-malachite green (LMG) was followed for 100 days in glass eels ( Anguilla anguilla). The eels at an average weight of 4.1 g were exposed to MG at a nominal concentration of 0.1 mg l −1 bath water for 24 h at a water temperature varying between 23.0 and 26.5 °C. After treatment, the juvenile fish were transferred into a tank containing MG-free water. The tank was integrated in a recirculation water supply system of an eel farm. At regular time intervals, 10 fish and a water sample were collected for high-performance liquid chromatography (HPLC) analysis. The highest average concentration of MG green was found at 435±59 μg kg −1 (mean±S.D.) whole body material at 6 h after the start of the treatment. The LMG metabolite concentrations were relatively high (>100 μg kg −1) and stable between approximately 2 h after the start of the treatment and 1500 h after the end of the treatment with a maximum averaged concentration at 831±231 μg kg −1 whole body material. At 2400 h after exposure, LMG was still present at an average level of 15±12 μg kg −1 whole body material, although the fish had not gained weight. The parent drug MG was not detectable at the last analysis points 1920 and 2400 h after treatment. Residues of MG were not detectable in the recirculating and biofiltered water. In addition to this experiment, two fast-growing eels at an age of 11 months were analysed at their slaughter weight of 0.1 kg. At their glass eel life phase (0.3 g body weight), these animals had been treated at 0.15 mg l −1 MG. Muscle tissues of the fish did not contain detectable amounts (