DETERMINATIONS OF PLASMA-VOLUME, EXTRACELLULAR FLUID VOLUME, AND TOTAL-BODY WATER IN CHANNEL CATFISH

Volumes of plasma, extracellular fluid, and total body water were estimated with indicator-dilution techniques in the adult channel catfish (Ictalurus punctatus). The experiments were performed with catheterized, nonsedated channel catfish restrained in flow-through, Plexiglas environmental chambers. Marker substances used to estimate body fluid volumes were Evans blue for plasma, sodium thiocyanate for extracellular fluid, and antipyrine for total body water. For comparisons, total body water was also estimated by desiccating fish to a constant weight. Plasma volume was determined to be 28.1 +/- 6.2 mL/kg body weight (mean +/- SD), extracellular fluid volume was 183.2 +/- 34.6 mL/kg, and total body water was 531.3 +/- 76.4 mL/kg. Total body water volume estimated by desiccation was 664.1 +/- 50.8 mL/kg.