Technique and Landmarks
With the fish in ventral recumbency, insert the needle into the mouth and on the midline where the gill arches on each side meet until contact with bone is made. Slightly withdraw the needle until blood appears in the needle hub. This is easier to perform in a fish that has a large mouth opening.
Insert the needle on the ventral midline just anterior to the heart. The heart is located in the most anterior ventral part of the body cavity.
Insert the needle on the ventral midline into the heart (located in the most anterior ventral part of the body cavity). In small fish, this procedure may be lethal.
Duct of Cuvier or common cardinal vein
Lift the operculum and insert the needle behind the 4th gill arch, directing the needle caudally so it enters the isthmus of the body.
This technique is only suitable for large fish (total length, >700 mm). Insert the needle directly into a gill arch until an artery is reached.
Lateral approach: Insert the needle at a 45° angle just below the lateral line of the caudal peduncle, and advance cranially until contact with the vertebral column is made. Then direct the needle ventral and lateral to the vertebral column as the syringe is gently aspirated.
Ventral approach: Insert the needle on the ventral midline and advance dorsally until contact with the vertebral column is made, and then withdraw slightly.
Fish should be sedated or anesthetized prior to blood collection.