Comparison of free amino acid contents in plasma, whole blood and erythrocytes of carp, coho salmon, rainbow trout, and channel catfish.

Abstract

Contents of free amino acids (FAA) and related compounds were examined in plasma, whole blood, and erythrocytes of four species of freshwater fishes: carp Cyprinus carpio, coho salmon Oncorhynchus kisutch, rainbow trout Salmo gairdnerii, and channel catfish Ictalurus punctatus. The content of each FAA in the erythrocytes washed with saline was always low in all species and about 20-60% of the calculated erythrocytes (CE) content which was estimated from the whole blood and the plasma content. This result probably indicates that FAA in the erythrocytes of fishes were washed out by rinsing. In carp, coho salmon, and rainbow trout, the total amounts of essential FAA in the CE were similar or slightly higher than those found in the plasma, while the total amounts of nonessential FAA in the CE were two to three-fold higher than those found in the plasma. In channel catfish, however, both total amounts of essential and nonessential FAA in the plasma were about one-fifth of those in the CE. The CE levels of phosphoserine, taurine, aspartate, glutamate, and ammonia were 7-30 times higher than the plasma levels. On a percentage distribution basis, the plasma contents of these compounds were only 4-16% of those in the whole blood.