142 Conservation Department 



soon as analytical samples have been taken the blood is centri- 

 fuged, to a constant cell volume. From the reading on the cen- 

 trifuge tube the per cent of erythrocytes (red blood cells) by 

 volume can be determined. 



In order to obtain blood from fish the heart must first be located 

 and the position of the ventricle must be determined. The ventri- 

 cle is the safest place to puncture since its thick walls close 

 immediately after the needle is removed. This prevents any hem- 

 orrhage after the operation. If several specimens of a given 

 species are available it is best to dissect one and locate the heart 

 accurately. If only one specimen is at hand and blood must be 

 obtained, it is best to place it on its back and to pierce the ventral 

 surface at the half-way point on a line drawn between the fore- 

 most points of attachment of the pectoral fins. 



This general technique is applicable to all fish except those 

 belonging to the species of catfishes (Ameiurus). For these we 

 have usually opened the gill cover, pierced the membrane directly 

 under the gills, and gone into the heart from the left side with the 

 specimen lying on its right side. We have employed this tech- 

 nique when working upon all closely related species except the 

 large specimen of lake catfish {YiUarius lacustris). We have been 

 able to obtain samples easily from this specimen by piercing the 

 ventral surface in the manner used normally. The reason for the 

 employment of this special technique in the case of the Ameiurus 

 is the excellent protection of the heart by the pectoral girdle. 

 Unless the specimen is unusually large, one is forced to injure 

 the liver in getting into the ventricle of the heart of species of 

 Ameiurus in this manner. 



Varying amounts of blood have been withdrawn from fish. The 

 greatest taken in the course of the experiments are thirty cubic 

 centimeters (about one ounce) in a single bleeding from the 8 

 ])ound specimen of lake catfish (YiUarius lacustris). ^lore could 

 undoubtedly have been obtained but none of our experiments 

 required more than fifteen cubic centimeters. Fifteen cubic cen- 

 timeter samples have frequently been taken from four and five 

 pound carp without any apparent effect upon their activity or 

 vigor. In contrast to the higher, warm blooded mammals, fish can 

 stand much greater losses of blood. The rat or dog is endangered 

 if more tlian a fourth of its blood is removed at any one bleeding 

 and if the hemoglobin is reduced below forty to fifty per cent. 

 In contrast, we are able to draw unusually large amounts at one 

 time from a fish and it seldom shows ill effects. We have reduced 

 the hemoglobin of the blood of carp below a value of ten per 

 cent, leaving the healthy fish still able to swim and with noi-mal 

 reactions. 



All hemoglobin determinations were made according to the 

 method of Cohen and Smith.* In this method the amount of 

 hemoglobin in the blood is determined by dissolving a carefully 

 measured volume of the unknown blood in tenth normal hydro- 



Cohen, B. and Smith. A., J. Biol. Chem. (1919) 39, 489. 



