Sixteen juvenile European cuttlefish (Sepia officinalis) were studied following a single intravenous injection or bath for antibiotic application of enrofloxacin. All animals were housed individually in floating bins within a 11370 liter (3000 gallon) seawater recirculating system kept at 24-27°C. The cuttlefish were haphazardly picked from a tank raised population of 80 and put into two groups of eight. Within each group of eight, six were given enrofloxacin. The group receiving the intravenous injection was given 5 mg/kg IV in the muscular portion of the cephalic vein. The mean weight of this group was 114.7 g. The other group was placed in individual 8L baths at an enrofloxacin concentration of 2.5 mg/L for five hours. Water samples were taken to ensure concentration levels. The mean weight of this group was 98.1 g. Magnesium chloride was used to anesthetize animals for all injections and collections; 0.3ml of hemolymph was collected at each time point. Hemolymph sampling occurred at 0.5, 2, 6, 24, 72 hours for three animals and at 0, 1, 3, 12, 48, 96 hours for three animals following injection or after bath treatment. The remaining two cuttlefish were used as controls and sampled at 0, 2, 6, 24, 48, 72 hours. Hemolymph was centrifuged and frozen at -70°C until samples were analyzed by high performance liquid chromatography (HPLC). In both studies no controls had detectable drug concentrations. Standard curves were performed for each day of HPLC analysis and no detectable ciprofloxacin metabolite was seen. In the IV study, drug was detectable through either 3 or 6 hours, except in one animal in which it was detected at 12 hours. Mean Cmax is 85.3 µg/ml. In the bath study, drug was detectable through either two or three hours. Mean Cmax is 4.9 µg/ml. There were no mortalities associated with this research.
To verify that the IV injection had circulated uniformly to vascular sites other than the injection site, two different animals were sacrificed. Both cuttlefish received the standard 5 mg/kg IV injection. The animals were anesthetized, surgically opened, and hemolymph collected from a branchial heart. Euthanasia followed the half hour and one hour sample collections. Enrofloxacin was found at levels comparable to those time points in the IV study.
The authors would like to thank Jonathan Minton and Leigh Walsh for their assistance with the animals.