Veterinarians are now seeing ornamental fish patients on a regular basis and our knowledge of how to manage the pet fish patient is increasing rapidly.1-5 A large percentage of these patients are koi (Cyprinus carpio), taxonomically an ornamental carp. Koi have been selectively bred in Asia for hundreds of years with qualities such as color, pattern, size, and conformation of utmost importance in terms of desirability and value. Some of these fish can be quite large and at times difficult to handle. Injectable antibiotics and other chemotherapeutants are frequently administered multiple times as part of the therapeutic plan for a variety of infectious diseases.6-8 Intravenous catheterization of fish is possible but technically challenging, time-consuming, and risky. The ability to administer drugs safely and effectively to the intracoelomic cavity without capturing and restraining the fish will reduce stress and risk to both the fish patient and the caregiver. The technique for temporary catheter placement described in this report has been found to be safe, inexpensive, and effective in the koi.
Twelve approximately two year-old koi were obtained from a North Carolina fish farm. Six of the fish were randomly selected for catheter placement. The fish were anesthetized with 200 mg/L buffered tricaine methanesulfonate (Finquel, Argent Chemical, Redmond, WA, USA). A stock solution of tricaine methanesulfonate was prepared by dissolving one gram of Finquel and one gram of sodium bicarbonate in 100 mls of distilled water, yielding a stock solution of 10 mg/ml buffered tricaine methanesulfonate. A surgical plane of anesthesia was maintained using the FADS (fish anesthesia delivery system)9 with recirculating water containing 100 mg/L buffered tricaine methanesulfonate.
Using the following technique, a 23-gauge 3/4-inch butterfly catheter (Becton Dickinson, Franklin Lakes, NJ, USA) was inserted into the coelomic cavity of each fish and then secured. With the anesthetized koi in right lateral recumbency, the sterile needle of the butterfly catheter (wings removed with sharp scissors) was placed between scales at an approximately 20 degree angle to the body wall in the area just above the caudal edge of the left pelvic fin. The dorsal aspect of the left pectoral fin was used as a landmark for consistent placement of the catheters (imaginary, perpendicular lines were drawn between the dorsal pectoral fin insertion and the caudal edge of the pelvic fin). Once placed, the catheter was tested for patency with approximately 0.1 mls of heparinized saline (100 units heparin in 250 ml saline). The plastic hub of the catheter was secured to the skin using a single simple interrupted 4-0-nylon suture (Monosof, US Surgical, Norwalk, CT, USA). The catheter was then looped cranially and secured with a second skin suture over the left dorsal epaxial musculature. A single drop of cyanomethacrylate (Vet Bond, 3M, St. Paul, MN, USA) was applied to the needle insertion site and a small amount of povidone iodine ointment applied to both suture sites using a cotton swab.
Finally, an injection port (Johnson & Johnson, Cincinnati, OH, USA) was secured to the free end of the catheter and the entire catheter flushed with 0.4 mls of heparinized saline. At this point the fish was removed from the FADS and returned to its tank for uneventful recovery.
The catheters were flushed daily for six days with 0.4 mls of sterile heparinized saline without removing the fish from the tank. This daily catheter treatment was used to simulate a chemotherapeutic injection and to keep the catheter patent. The fish behaved and fed normally during this six-day interval and all of the catheters remained secure and patent.
At the end of the sixth day (144 hours) each of the catheterized koi and control koi were individually anesthetized with 200 mg/L tricaine methanesulfonate and weighed. A 10 mg/kg enrofloxacin (Bayer, Shawnee Mission, KS, USA) dose was computed and administered to each fish. The enrofloxacin dose was given to the catheterized fish via the injection port and followed with 0.4 mls of heparinized saline. The control fish were given a single injection using a 23-gauge needle in the same site as the catheter placement. After flushing, each catheter was removed from the fish using scissors and forceps to free the sutures.
Approximately 0.8 ml of heparinized whole blood was taken from the caudal vein of each fish at time zero and at the following times post drug administration: two, four, eight, 12, 24, 48 and 72 hours. Prior to HPLC assay, aliquots from each fish's time point sample were pooled (catheter and control groups separately) in an effort to reduce the total number of samples analyzed.
All 12 fish continued to behave and feed normally following the catheterization. While there was a noticeable amount of inflammation associated with the sutures and hub of the catheter, these lesions resolved and were not detectable six weeks after the catheters were removed.
The maximum plasma concentration (Cmax) of enrofloxacin was 4.72 µg/ml obtained at 12 hours following needle injection and declined to 2.48 ug/ml by 72 hours. The Cmax of enrofloxacin was 5.76 µg/ml obtained at four hours following catheter injection and declined to 1.95 ug/ml by 72 hours.
The primary objective of this study was to determine the safety and efficacy of an intracoelomic catheter in koi utilizing plasma levels of enrofloxacin. A secondary objective was to establish an intracoelomic-dosing regimen for enrofloxacin in the koi. While this study does not address a specific bacterial pathogen, the existence of in vitro MIC data supports the statement that effective plasma concentrations of enrofloxacin can be obtained in the koi after a single ten-mg/kg intracoelomic injection (either via catheter or needle). The Cmax of enrofloxacin in both test groups easily exceeded the in vitro MIC for 20 bacterial organisms known to infect fish.10 For the majority of these organisms, the koi enrofloxacin Cmax was more than 40 times greater than the MIC.
There was no significant difference between the pooled plasma enrofloxacin levels of the catheterized koi and the control koi. It also appears that an intracoelomic catheter can be successfully and safely maintained in a koi for a period of at least six days. This would be highly beneficial for the veterinarian, client, and patient, especially in clinical situations where an intracoelomic drug would require daily or more frequent dosing.
This work was supported by grants from the United States Department of Agriculture, the United States Israel Binational Agricultural Research and Development Fund, and North Carolina Sea Grant. The authors wish to thank Shane Boylan, Larry Christian and Maureen Trogdon for their help and assistance.
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