Persistence of malachite green in tissues of rainbow trout after a long-term therapeutic bath

Abstract

The goal of this paper was to test the time of malachite green persistence in rainbow trout after long-term bath as well as to evaluate the quality of randomly sampled marketable rainbow trout from the point of view of malachite green residues. A 6-day-lasting therapeutic bath of rainbow trout was performed in malachite green of 0.2 mg.l-1 concentration. Its residues were then observed in muscle, liver and skin of treated fish. Immediately after the bath, malachite green was detected in muscle, liver and skin at the levels of 0.712 ± 0.383, 0.834 and 0.649 mg.kg-1, respectively, as a sum of both coloured form and leukoform. Eight weeks after the bath, an expressive decrease of the coloured form of malachite green was found while its leukoform was detected in fish as late as after 10 months. Results of analyses were found negative twelve months after the bath. Marketable rainbow trout were randomly sampled for checking the malachite green content on 12 trout farms in the Czech Republic in 1993-1995. Malachite green was found in 2 case (in 1 of them only as a slightly increased value in skin) while all other findings were negative. Hence, the results of our study indicate that malachite green persisted in the treated fish as a leukoform for 10 months. It was evident that the 6-months withdrawal lime, recommended in the Czech Republic was insufficient. In case of the frequent one-and-half-year-long productive cycle of rainbow trout we therefore do not recommend to carry out therapeutic baths in malachite green for fish older than 6 months.