A cannulation technique for urine collection from haddock, Melanogrammus aeglefinus L.

Urine collection from fish is an integral part of metabolic studies designed to measure the excretion of various biochemical compounds. The techniques developed for urine collection in salmonids cannot be applied to gadoid fish due to the anatomical differences in their urinary system. The anterior ureter of haddock (Melanogrammus aeglefinus L.) is an elongated duct that originates from the anterior part of the trunk kidney and courses dorsal‐posterior to the region of the uropore. The posterior ureter originates from the middle of the caudal kidney, and eventually fuses with the anterior ureter before forming a small urinary bladder. After the two ureters join together, a short common duct empties into the urinary bladder and terminates at the uropore behind the anus. Just before the end, the terminal posterior ureter takes a sharp U‐shaped turn, which makes cannulation difficult. We investigated the development of a cannulation technique for urine collection in three different‐sized groups of juvenile haddock. In anaesthetized fish, a catheter was inserted in the uropore in a posterior direction to follow the U‐shaped course of the ureter. After insertion of the catheter into the uropore, the externalized segment of tubing was connected to a needle attached to a syringe. Urine was then aspirated from each of the 20 fish at 15 μL min^?1 for 5 min to measure urine volume and urinary phosphate concentration. The results were reproducible and this cannulation technique has potential for use in other gadoid metabolic studies.