Failure of flumisol bath treatments during commercial transport of Atlantic salmon smolts to prevent the activation of stress inducible furunculosis

Abstract

This paper reports the development of protocols for the bath administration of flumequine to Atlantic salmon ( Salmo salar L.) smolts during their transfer from a fresh water hatchery to a marine farm in buckets suspended under a helicopter. The fish were treated at a density of 365 kg m −3 in water of pH 6.3 and hardness 13.2 mg 1 −1 CaCO 3. Serum flumequine concentrations showed a linear increase with respect to time of the bath and were dose dependent. The addition of benzocaine to the baths had little effect on uptake during the first 20 min of the bath. 720 000 smolts with covert stress inducible furunculosis were transported to 20 sea cages during 180 helicopter trips in buckets containing 100 μg ml −1 flumequine and 5.7 μg ml −1 benzocaine. Furunculosis was detected in fish in all sea cages shortly after transfer and the treatment was considered to have failed to control the activation of the covert infections. The pharmacokinetics of flumequine were determined in fish that were introduced to sea water at the termination of a bath treatment in fresh water. This data was compared to that obtained from fish that remained in fresh water following a similar treatment. The introduction of the fish into sea water resulted in a very rapid excretion of flumequine via the intestine. It is argued that this rapid elimination of the antimicrobial agent may have been an important factor in the failure of the bath treatment under commercial conditions.