Abstract

There is an increasing amount of information available on administration and maintenance of anesthesia in fish. Very little is known about the clinical response of fish to their time out of water during a complete office physical exam. This study examined the blood gases and behavior of fish when exposed to a treatment similar to that of a typical office visit. Ten hybrid striped bass (Morone saxatilis) of uniform age (6 months) and similar size (17-22 cm length) were used for this study. The fish were housed in a North Carolina State University (NCSU) fish production facility and maintained with adequate nutrition and water quality. The subjects were exposed to identical treatments of four distinct periods of interest marked as pre-anesthesia (after acclimation in holding tank), anesthesia, anesthesia-a, and post-anesthesia. The first two treatments involved placing the individual fish in a holding tank with 14 L of home aquarium water, while the last two treatments were performed with the fish out of water in room air. The holding/anesthetic tank was aerated and supplied with water from the home tank. A period of 5 minutes was allowed for acclimation in the holding tank. All 10 fish were anesthetized with tricaine methanesulfonate 200mg/L (MS-222, Argent, Redmond, WA) until all voluntary movement ceased (stage IV anesthesia), or a 3-minute anesthetic immersion was complete, whichever came first. A volume of 0.2-0.3 ml of blood was collected from the sinus venosus via a lateral opercular approach using sodium heparinized 1.0 cc syringes for each experimental treatment. Samples were analyzed immediately after collection using EG7+ cartridges (i-STAT Corporation, East Windsor, NJ) in an i-STAT portable clinical analyzer (Heska, Waukesha, WI). Dissolved oxygen and water temperature were recorded at each sampling using an YSI dissolved oxygen meter (YSI Incorporated, Yellow Springs, OH). The pH and blood gas values were corrected to body temperature, which was assumed to be equal to the ambient water temperature, at the time of blood sampling. Venous PO2 of each individual fish was normalized by multiplying the barometric pressure of the atmosphere by the fractional concentration of oxygen in the atmosphere and the percent oxygen saturation of water at the time of blood sample collection. This value was then divided into the measured venous PO2 (via i-STAT) to attain a Venous Blood Oxygen Index (VBOI), a more accurate determination of blood oxygen levels. Respiratory rates, determined as complete opercular movements, were recorded immediately prior to each sampling. Values from each period (pre-anesthesia, anesthesia, anesthesia-a, and post-anesthesia) were compared to each other. Data were analyzed with statistical software (SigmaStat, Jandel Scientific, San Rafael, CA) using One-way ANOVA and Tukey post hock tests. Differences of P<0.05 were considered to be statistically significant.

Acknowledgements

The authors wish to thank Dr. Anthony Blikslager for his assistance in this project.