Modification of the microhematocrit technique with trout blood

Commercial and laboratory‐prepared capillary tubes for hematocrit were tested. A 10 percent solution of heparin was found to be best for the preparation of treated capillary tubes. For examination of trout blood laboratory‐prepared capillary tubes were found to be superior to commercial tubes which are designed for human blood. Sharp, pointed heparinized capillary tubes were used with good results for collecting blood from the heart without killing the examined fish. Hematocrits determined directly in such tubes were found to have the same value as those prepared in other ways.