Treatment of trichodiniasis in eel (Anguilla anguilla) reared in recirculation systems in Denmark: alternatives to formaldehyde

Treatment of trichodiniasis in recirculation eel farms using formalin (37%) has been found insufficient. We have screened 30 different chemical substa nces for efficacy against natural infections with trichodinids (Trichodina jadranica) on skin and gills of eels. The following substances showed high parasiticidal effect: acriflavin (25 ppm), bithionol (0.1 ppm), chloramine T (50 ppm), Detarox AP(R) (45 ppm), malachite green (1 ppm), raw garlic (20 0 ppm), potassium permanganate (20 ppm) and Virkon PF(R) vet. (20 ppm). Pre liminary screening revealed that the anthelmintic, bithionol, and the decom posable disinfectants Detarox AP and Virkon PF(R) vet. were potential thera peutics and these were tested on infected eel stocks in recirculation produ ction units. The following treatments showed a high parasiticidal effect: b ithionol at 0.1 ppm in a recirculation system including the biofilters; Det arox AP(R) (45 ppm) in recirculation systems with the biofilters temporaril y isolated for 1 h and Virkon PF(R) vet. (40 ppm; 25 ppm at start supplemen ted with 15 ppm 1 h later) in rearing tanks temporarily isolated from recir culation systems for 3 h. (C) 2000 Elsevier Science B.V. All rights reserve d.