Toxicity of formalin for fingerlings of var. and in vitro efficacy against Kulwièc, 1927 (Monogenea: Dactylogyridae).

The toxicity of formalin on var. and its anti-parasite effects against (Monogenea) in in vitro tests is analyzed. Specimens of were submitted to eight concentrations of formalin: 50, 75, 100, 125, 150, 175, 200, 250 mg L, in triplicate. Concentrations of formalin 100, 150 and 200 mg L were then tested to determine the median lethal concentration of 50% of the fish per immersion bath. Fish behavior was also observed during the first 6 h of exposure. The 200 mg L concentration was the most rapid efficacy for , killing all parasites in 16 min. All parasites were killed in 47 min at concentration 100 mg L. Concentration 200 mg L was the most lethal for fish in less than 24 h exposure, with 24 h LC at 135.44 (119.78-153.14) mg L. The therapeutic index was 2.05-30 min and 1.15-16 min. A short bath (1 h) is recommended in koi carp with a minimum concentration of 75 mg L of formalin, not exceeding 100 mg L for treatment against