Few studies have yet addressed the functional aspects of MHC molecules in fish. To lay the foundation for this, we evaluated the association between disease resistance and MHC class I and class II polymorphism in Atlantic salmon. Standardized disease challenge trials were performed on a semi-wild Atlantic salmon population with subsequent MHC typing and statistical analysis. The pathogens employed were infectious salmon anaemia virus (ISAV) causing infectious salmon anaemia and the Aeromonas salmonicida bacteria causing furunculosis. The material consisted of 1,182 Atlantic salmon from 33 families challenged with A. salmonicida and 1,031 Atlantic salmon from 25 families challenged with ISAV. We found highly significant associations between resistance towards infectious diseases caused by both pathogens and MH class I and class II polymorphism in Atlantic salmon. The observed associations were detected due to independently segregating MH class I and class II single loci, and inclusion of a large number of fish allowing an extensive statistical analysis.

The plasma pharmacokinetic profile of the antibacterial agent florfenicol was studied in Atlantic salmon Salmo salar in seawater. In a single‐dose study, each fish was given 10 mg/kg body weight by intravenous (iv) injection or by oral gavage of feed coated with the drug. In a multidose study, pelleted feed coated with 2 g florfenicol/kg was hand‐fed daily for 10 d at a dosage of 10 mg florfenicol/kg body weight. The pellets contained small, X‐ray‐dense glass beads (hallotini). The feed intake was assessed by counting the number of ballotini on X‐ray pictures of sampled fish. In a depletion study, the concentration of the marker residue, florfenicol amine, was determined in muscle and liver after a field trial in which the fish were medicated with feed coated with florfenicol for 10 d at a dosage of 10 mg/kg body weight. In the single‐dose study, the iv data were best described by a two‐compartment open model; the elimination half time. t1/2β, was estimated at 14.7 h. The maximum plasma concentration was 9.l μg/mL, observed at 6 h. The bioavailability was 99%. The maximum plasma concentration observed in the multidose study and the maximum concentration predicted from the single‐dose study corresponded very well, which demonstrated the value of single‐dose studies. In the depletion study, the upper 95% confidence band for individual observations intercepted the limit of detection for the analytical method after 21 d in muscle and after 27 d in the liver.

No abstract

Four challenge methods, intraperitoneal (i.p.) and intramuscular (i.m.) inoculation, bath and cohabitation exposure, were evaluated as methods for testing the efficacy of furunculosis vaccines in Atlantic salmon, Salmo salar L. Groups of fish vaccinated with one of two different vaccines containing aluminium phosphate or animal/vegetable oil as an adjuvant were challenged with Aeromonas salmonicida 6 and 12 weeks after vaccination. Relative per cent survival (RPS) was calculated daily during a 3‐week observation period post‐challenge. A large variation in protection measured by RPS, both between methods and between different time points for each method, was found. Towards the end of the observation period, RPS tended to be similar in the i.p. and cohabitation challenge groups. A high degree of protection was demonstrated for the oil adjuvanted vaccine. The i.m. challenge produced very low RPS numbers for both vaccines, but this was most marked for the aluminium‐phosphate‐adjuvanted vaccine. The bath exposure resulted in RPS values intermediate to the cohabitation and injection methods. The study also demonstrated that, after i.p. and i.m. challenges, the initial peak mortality caused by the inoculation was followed by a secondary increase in mortality, probably because of shedding of bacteria into the water during the first mortality phase and hence contributing to a superinfection state.

The efficacy of florfenicol in the control of natural outbreaks of furunculosis in Atlantic siiltnon, SatiHO sutitr L. was cvalucitcd on five Norwegian farms duntig the sutnmcr of 1992. A total of 115 245 first-or second-generation fish received florfenicol with feed at a dose rate of lOmgkg"' body weight daily for 10 eonseeutivc days. Comparisons were made with similar pens offish medicated with the preferred treatment for eaeh location. In the 10 days following introduction of therapy, all treatments were associated with a rapid decline in mortality caused by infection with Aeromonas satmontcida. Florfenicol-medicated salmon had a lower specific mortality than those given oxolinic acid, flumequine or a trimethoprim and sulphadiazine eombination. No adverse reaetions to treatment with florfenieol were observed.