Free amino acids and ninhydrin-positive substances in fish--II. Cardio-respiratory system: plasma, erythrocytes, heart and gills of the rainbow trout (Salmo gairdnerii Richardson).

1. Free amino acids and ninhydrin-positive substances were studied in blood plasma, erythrocytes, heart and gills of rainbow trout using ion exchange automatic chromatography. 2. In comparison with plasma, only few amino acids have higher levels in red cells: aspartic and glutamic acids, glycine. 3. In heart and gills total amino acid level is greater than in blood. Levels are similar in both tissues except glutamic acid which is higher and histidine which is lower in gills. 4. The main ninhydrin positive substance is taurine which has very high level in erythrocytes, heart and gills, much more than in previously studied muscle and skin.