The folowing two images are enlarged to show detail. The tail has been removed from a fish which has been euthanized due to a tumor. The section is just posterior to the anal fin. The koi is held upside down such that the ventral surface is up. You are looking from the tail towards the head. The anal fin is visable at the top of the photo. The needle is a 11/2 inch 22 gauge with the tip in the area of the caudal vein.
By drawing blood from this area by the ventral approach, there are no critical organs for the needle to penetrate between the surface and the vein. If a scale is damaged, it is not visable from above while healing.
One essentially inserts the needle in the midline, aiming for the center of the vertebral body. In smaller and medium size koi, one feels resistance at the vertebral body and then gently withdraws the syringe plunger. If blood does not immediately flow, the plunger is released and the needle repositioned. If suction is maintained on th plunger while repositioning the needle, the usual result is a cloged needle. In very large koi, It is a matter of positioning as the scales and tissues are very thick and tactile sensation is markedly reduced. Different techniques for supporting the koi are utilized depending on size of koi and personal preference. Examples follow here and on other pages. The site of venipuncture is swabbed with betadine before the fish is measured, photographed, and returned to the pond.
In this case, the koi is immersed in aerated water and the tail is held with a wet towel. The watch should have been removed before handling koi.
Blood is withdrawn form the caudal vein.
One ml of blood is more than enough.
DIsinfecting the venipuncture site with iodine solution.
The blood is transferred from the syringe to the sterile sample tube. As the tube is under a vacumn, the syringe plunge is initially held to prevent the rapid flow of blood from the syringe. The needle is usually held against the side of the tube as well. These measures are important in reducing red cell hemolysis.
For some reason, it helps to hold the needle cap in one's mouth.
Gently withdrawing blood.
Recovery in measuring and photo tub.