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Blood may be withdrawn from a number of sites but the preferred site is the
Caudal vein using either a lateral or ventral approach. Entry site for the needle is approximately half way along the Caudal
Peduncle, for the lateral approach the needle is inserted just below the lateral line angled towards the head. When the bony
vertebral column is encountered the needle is angled slightly below to enter the Caudal vein. For the ventral approach the
needle is inserted in the ventral mid line along side, or just Caudal to the anal fin. When the vertebral column is encountered
the needle is withdrawn slightly to enter the Caudral vein. Fish blood is readily prone to haemolysis for this reason as little
vacumn should be put on the syringe as possible and vacumn blood collection tubes should be avoided. These methods will usually
obtain blood from fish weighing over 25g, in smaller fish, sadly, to obtain a blood sample, they have to be sacrificed and
the tail cut off to expose the Caudal vein, but great care must be taken not to dilute or contaminate the sample. Since fish
blood clots rapidly Heparin is the most useful anti-coagulant and all the equipment used (i.e. needles and syringes) should
rinsed in Heparin.
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