OBJECTIVES: The aim of this study is to assess the effects of a treatment bath in a formalin solution on fish, focusing on haematological, biochemical and histopathological profiles. METHODS: A total of 96 common carps (Cyprinus carpio) were randomly assigned to eight groups. Four experimental groups were placed in the test solution for 60 minutes. The concentration of the formalin bath was 0.17 ml/l (38% formaldehyde), with the water temperature of 20°C. The effects of the bath were monitored immediately (E0) and 24 hours (E24h), 48 hours (E48h) and 10 days (E10d) after the bath. There was a control group (C0, C24h, C48h, C10d) for each of the experimental groups. RESULTS: Histopathological indices were strongly affected. Extensive changes were found on gill and skin immediately and also after 24 h, 48 h and 10 d of the formalin treatment bath. A plurality of mucinous elements was observed on the skin. Moreover, structural devastation of lamellas and numerous mucinous cells were observed on the gill. Changes were also found in haematological and biochemical indices. CONCLUSIONS: It can be concluded that after applying the treatment bath in the formalin solution, the monitored profiles were affected immediately after the bath and also after 10 days (histopathological changes of skin and gill). Such significant impact of therapeutic formalin bath should be considered in treatment of fish.

Department of Anatomy Histology and Embryology Faculty of Veterinary Medicine University of Veterinary and Pharmaceutical Sciences Brno Czech Republic

Department of Animal Protection Welfare and Behaviour Faculty of Veterinary Hygiene and Ecology University of Veterinary and Pharmaceutical Sciences Brno Czech Republic

Department of Territorial Studies Faculty of Regional Development and International Studies Mendel University in Brno Czech Republic