This study was supported in part by the Food and Drug Administration, Center for Veterinary Medicine, Grant No. FDU-000059-02.

Abstract

Channel catfish were restrained for chronic blood and urine sampling over extended time periods in plexiglas chambers perfused with oxygen- and temperature-controlled water. The fish were instrumented with catheters placed in the dorsal aorta for blood collection, and into the urinary bladder for urine sampling. Additionally, sampling ports in the chambers allowed for repeated oxygen concentration and water temperature measurements throughout the experiments. The environmental chambers have been used for kinetic modeling experiments in which blood and urine were routinely sampled for up to 96 hours.

Introduction

Studies requiring frequent blood sampling over prolonged periods (48-96 hrs), or those studies in which several milliliters of a drug or chemical must be given intravenously with assurance are difficult to manage in the catfish. Fish may be restrained physically by boards or straps, or chemically to permit blood or fluid sampling; however estimating kinetic parameters such as half-life and clearance rate from xenobiotics of interest may be most meaningful in the intact, non-sedated animal. Additionally, intravenous injections and blood sampling via catheter are greatly simplified and probably more precise than by external puncture techniques. The current paper describes the flow-through chambers and sampling system that have been used in over 60 fish experiments to permit estimation of body fluid volumes, and to describe the pharmacokinetics of model compounds in the channel catfish.

Materials and Methods

Commercially available plexiglas (1/4 and 1/2 inch) was used for construction of the chambers. The tubular portion of the chambers varied in diameter from 7 to 10 cm and in length from 40 to 55 cm to accommodate varying sizes of fish. The tube was supported 16 cm above table-top level by plexiglas end pieces. The tube was drilled to position 13 mm holes for catheter exiting to the outside of the chamber, and for water inflow and outflow. The tube was cut crosswise, and collars made from plexiglas were attached to the cut edges to permit opening and closure of the chamber.

Water pumped to the chambers was conditioned in a Min-O-Cool (Frigid Units, Inc., Toledo, OH) tank. The water was chilled or warmed to the prescribed temperature, and the level of oxygen concentration desired was maintained by constant aeration. Water was pumped through the fish chambers by a variable speed roller pump (Cole-Parmer, Chicago, IL).

Blood collection catheters were polyethylene (0.86 mm ID x 40 cm) (Becton-Dickinson, Oxnard, CA), and were introduced into the dorsal aorta via a 15 ga x 6 cm needle. Urinary catheters were pediatric Foley (8 Fr.) catheters attached to polyethylene extensions.

Results and Discussion

To date, more than 60 fish have been housed in the plexiglas chambers for periods of 4 to 96 hours. Catheters for blood and urine collection were passed through rubber stoppers so that sampling could be performed outside the chamber and avoid handling the fish. The catheters for blood sampling were filled with heparinized saline solution (4 units/ml) to prevent clot formation.

Water temperature was maintained + 1/2 degree C during experiments by heaters or chillers as appropriate. Dissolved oxygen concentration ranged from 6 to 8 ppm, indicating adequate aeration of water in the reservoir. Water flow rate into the 6 liter chambers was regulated at approximately 350 mi/min, which was sufficient to prevent variation in water temperature or dissolved oxygen concentration in the chambers compared to the water reservoir.

Experiments performed in the chambers have included estimation of plasma volume, blood volume, extracellular fluid volume, and total body water in the channel catfish. Also the pharmacokinetics of xenobiotics of interest have been estimated following intravenous, intramuscular, and oral administration using the chamber system. Further studies could include residue kinetic modeling of antibiotics or other therapeutic agents, toxicity experiments, or metabolism studies in the catfish.