Figure l. — Diagrammatic representation of the centrifuge 

 method for extracting serum from small fishes. A. Blotted fish 

 ready for bleeding. B. Fish is wrapped with Kimwipe, leavmg 

 overlap at top. Vent is also covered to prevent contamination of 

 the sample. C. Caudal peduncle is cut at an angle with sharp 

 scissors. D. Fish is fit snugly into a 15 ml centrifuge tube, usmg 

 more or less Kimwipes to obtain a proper fit, and taped so the fish 

 will not be pulled into the tube. E. Fish , in the tube, is spun at 400 

 g for 3 min. F. Covered tube with blood is kept in an ice water 

 bath until another fish can be processed in the same tube. 



serted, tail first, into a 15 ml Pyrex centrifuge tube 

 and secured by taping the overlapping Kimwipe to 

 the side of the tube (Figure ID). (The fit must be 

 snug but not too tight). Varying fish sizes can be 

 compensated for by wrapping with more or less 

 Kimwipes; fish will not be pulled into the tube if 

 the wrapping is correct. Fish are spun in a cen- 

 trifuge at 400 g for 3 min. After each fish is cen- 

 trifuged, the tube of blood obtained (one tube for 

 all fish) is covered and quickly placed in a beaker 

 of ice water to inhibit evaporation of serum ob- 



tained and hemolysis of red blood cells. A total 

 pooled sample of approximately 1 ml can be col- 

 lected from 20 fish. The blood is allowed to clot and 

 the serum drawn off. From 1 ml of pooled whole 

 blood, 0.5 ml of serum can be obtained. 



Discussion 



Contamination by tissue fluid, lymph, and cell 

 debris is unavoidable but exists in any method 

 which severs the caudal peduncle. Proper wrap- 

 ping of fish and the use of sharp scissors help to 

 reduce this contamination. The amount of lymph 

 and intracellular fluid gained from the cutting 

 action of the scissors and centrifugation is mini- 

 mal and does not prejudice one's results sig- 

 nificantly. Cellular debris from the actual wound 

 is insignificant because the serum is separated 

 from it before analysis. Careful placement of 

 Kimwipes around the vent eliminates urine or 

 feces contamination of the sample. This method 

 has the advantage of simplicity, speed, and no 

 anticoagulant contamination. Red blood cell 

 hemolysis is minimal, and larger pooled blood 

 samples can be obtained in a single container with 

 little serum loss during unnecessary transfers 

 when heparinized collecting tubes are unfeasible. 

 This technique should be helpful in pathologic 

 studies of small fish used in toxicity tests when it is 

 desirable to monitor many blood serum parame- 

 ters and where there is no objection to the use of 

 pooled samples. 



Acknowledgments 



I thank Lee Courtney for help with the figure 

 and John Couch for critical review of the manu- 

 script. 



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510 



