Abstract

Blood volume in fish, as in most animals, is often estimated to be eight to ten percent of the animal's body weight. This value is frequently used when determining the amount of blood that can safely be drawn from a fish (generally assumed to be no more than 6-10% of the estimated blood volume). Overestimation of blood volume, however, can have deleterious effects on fish in situations involving withdrawal of large or repeated blood samples. Blood volume determination in mammals and birds is frequently done using radioactively labeled red blood cells. Safety concerns and increasing costs of disposal of radioactive material have made the use of radioactive compounds less desirable in biomedical research.

This study examines two alternative methods of measuring blood volume in fish. One approach measures total fluid volume using Evans blue dye to bind to the plasma proteins. The second method involves fluorescent labeling of erythrocytes. The percentage of labeled cells present in a blood sample is then determined using flow cytometry. Both of these methods were used in the evaluation of blood volume in three species of fish: hybrid striped bass, red pacu, and channel catfish. Blood volumes determined by each of the two methods were similar. The data acquired using both methods suggest fish blood volumes between 2% to 5% of body weight.

* Veterinary student presentation