Evaluation of the dorsal aorta cannulation technique for pharmacokinetic studies in Atlantic salmon (Salmo salar) in sea water.

The antimicrobial drug flumequine was given intravascularly and orally to cannulated and non-cannulated Atlantic salmon (Salmo salar) in sea water at 11 degrees C. The cannulated fish were divided into two groups, which were given flumequine (25 mg/kg) intravenously into the caudal vein (n = 8) and orally via a stomach tube down the oesophagus (n = 8). After a washout period of 2 days, the intravenously administered fish were given the drug orally, and the orally administered fish were given the drug intravenously. Blood samples were taken at different time points after drug administration through a cannula inserted into the dorsal aorta. The fish in the non-cannulated group were either given flumequine intravenously or orally, and blood samples were collected by killing five fish at predetermined time points after administration. The haematocrit values were measured in all the fish daily for 4 days after drug administration and thereafter, in all the collected blood samples throughout the whole experiment. The haematocrit values differed significantly between the cannulated and the non-cannulated fish. We found low haematocrit values and slow drug elimination in the cannulated groups, compared with higher haematocrit values and faster drug elimination in the non-cannulated groups, but further investigations are needed to prove any causal relations of this observation. The volume of distribution (Vd(ss)) was twice as large in the cannulated groups compared with the non-cannulated group, in the fish administered the drug intravenously. In the last part of the elimination phase, the half-lives differed considerably between the cannulated and the non-cannulated groups both after oral and intravenous administration. The slower depletion of the drug concentration in the plasma of the cannulated fish is due to the large Vd(ss) as there are only small differences in clearance (ClT) between the groups. In this study the elimination of flumequine in cannulated Atlantic salmon differed from the elimination of flumequine in non-cannulated Atlantic salmon.