ON PLASMA-VOLUME MEASUREMENT AND THE EFFECT OF EXPERIMENTAL STRESS INTHE MALE TILAPIA, OREOCHROMIS-MOSSAMBICUS, MAINTAINED IN FRESH-WATER

Plasma volumes in male tilapia (Oreochromis mossambicus) of different size were estimated following intracardial injection of radioiodinated human serum albumin (I-125-HSA), coupled with short-term, early sampl ing transient response analysis of I-125-HSA disappearance from the pl asma pool. This approach circumvents vascular marker leakage problems associated with constant steady state indicator dilution methods, mini mizes some sampling and mixing problems, and simplifies analysis of th e data. Changes in hematological parameters due to experimental stress were also studied, because the fish were not chronically cannulated. Results were used in a novel way to correct estimates of plasma volume upward by 15%, thereby providing a potentially useful alternative app roach to vascular volume measurement in species where stress-eliminati ng or reducing techniques, e.g., cannulation, are impractical or infea sible. Hematrocrits increased 38% at the onset, from 24.9% to 34.4%, a nd remained essentially constant during the 60 minute kinetic study, a nd plasma osmolalities increased 7%. Corrected plasma volumes V-p (mi) were a linear function of body weight(BW). The group mean V-p was 2.9 30% of BW and corresponding blood volumes were 3.9% of BW.