The influence of methylene blue and malachite green on common carp (Cyprinus carpio) blood parameters

Abstract

Methylene blue (MB) and malachite green (MG) are pharmaceuticals which were used in aquaculture to treat fish diseases for many years. Nowadays, they are prohibited in many countries, but illegal use is still reported. The aim of the present study was to evaluate the effects of these agents on blood parameters of juvenile common carp (Cyprinus carpio L.). The fish were exposed for 7 or 14 days to therapeutic concentrations of the drugs (2 mg/l in the case of MB and 0.2 mg/l for MG). The results indicate that fish treated with MB or MG showed inflammation and an anaemic response (minor in the case of MG). Moreover, increased erythropoiesis was observed in MB-treated fish. The results of the study indicate that these pharmaceuticals at therapeutic concentrations are toxic to juvenile common carp. MB proved to be more toxic than MG. Therefore, we advise against the use of these pharmaceuticals at the concentrations tested (even if permitted by the legislation of a given country). In our opinion, a ban on their use in fish intended for human consumption is justified.

Keywords

• methylene blue
• malachite green
• fish
• toxicity