Disappearance of malachite green residues in fry of rainbow trout (Oncorhynchus mykiss) after treatment of eggs at the hatching stage

摘要

The disappearance of malachite green (MG) residues was determined in fry of rainbow trout (Oncorhynchus mykiss) after six repeated treatments of the eggs at the hatching stage with MG oxalate at exposure levels of 1, 3 and 6mg lp# for 30min. Fry samples were taken from newly hatched fry (0days post-hatch, d.p.h.) and at regular time intervals at 16, 31, 43, 57 and 96d.p.h. The residues of MG and its major metabolite, leucomalachite green (LMG), were found to accumulate in the fry after MG treatments of eggs, with the highest residue levels being determined in the newly hatched fry. After exposures of 3mg lp# MG, mean concentrations of 1170pl106peg kgp# and 276pl38.6peg kgp# (n =3) were found in fry for LMG and MG, respectively. However, the disappearance of residues occurred rapidly in the fry, such that by 43d.p.h. only low levels of LMG could be determined. To confirm the elimination of residues, determinations were made also in fry muscle at 96d.p.h. but no residues were detected. The residues of MG in fry were determined by liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis with a limit of detection (LOD) of 0.5peg kgp# and a limit of quantification (LOQ) of 1.0peg kgp#. The accumulation as well as the elimination of residues correlated well with the level of exposure. During the study, the fry increased their weight, such that at the end of the study, their mean body weight was about 150 times greater than the mean body weight of the newly hatched fry. As the disappearance of residues occurred in conjunction with the growth of fry, the present results indicate that no residues of MG will remain in the fish intended for human consumption, if MG treatment takes place at the hatching stage under controlled conditions.