Efficacy of bithionol as an oral treatment for amoebic gill disease in Atlantic salmon Salmo salar (L.)

• Published in: Aquaculture
• Main Authors: Louwen-Skovdam, RL, Becker, J, Powell, MD
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier BV 2007
• Subjects: Agricultural and Veterinary Sciences; Fisheries Sciences; Aquaculture; Atlantic salmon; Salmo salar
• Online Access: https://doi.org/10.1016/j.aquaculture.2007.04.082; http://ecite.utas.edu.au/46343

This study examined the efficacy of bithionol as an oral treatment for Atlantic salmon Salmo salar affected by amoebic gill disease (AGD). The current commercial management strategy of AGD is a costly 3h freshwater bath. It is labour intensive and the number of baths needed appears to be increasing; hence, there is an effort to identify alternative treatments. Efficacy was examined by feeding AGD-affected Atlantic salmon twice daily to satiation with bithionol, an antiprotozoal, at 25mg kg- 1 feed. Three seawater (35, 17C) re-circulation systems were used each consisting of three tanks containing 32 Atlantic salmon smolts with an average ( SEM) mass of 90.4g ( 5.2). Three feeds were examined in the trial including bithionol, plain commercial control and oil coated commercial control. Feeding commenced 2weeks prior to exposure to Neoparamoeba spp. at 300 cells L- 1 and continued for 28days post-exposure. Efficacy was determined by examining gross gill score and identifying percent lesioned gill filaments twice weekly for 4weeks post-exposure. Bithionol when fed as a two-week prophylactic treatment at 25mg kg- 1 feed delayed the onset of AGD pathology and reduced the percent lesioned gill filaments by 53% and halved the gill score from 2 to 1 when compared with both the plain and oil controls during an experimental challenge. There were no palatability problems observed with mean feed intake of bithionol over the trial duration with fish consuming higher levels of the bithionol diet compared to both the oil and plain controls. This study demonstrated that bithionol at 25mg kg- 1 feed, when fed as a two-week prophylactic treatment for Neoparamoeba spp. exposure, delayed and reduced the intensity of AGD pathology and warrants further investigation as an alternative to the current freshwater bath treatment for AGD-affected Atlantic salmon. 2007 Elsevier B.V. All rights reserved.