Wm. Kirk Suedmeyer
Piscean medicine has rapidly progressed with the advent of improved techniques in aquaculture. This has extended to the veterinary field, where veterinarians play a critical role in preventive health care.5 The current and most popular techniques for fish phlebotomy are aspiration of the coccygeal vein or the heart.2-4 The tail is approached from a 45° angle just ventral and parallel to the lateral line and the needle is advanced to the ventral midline under, or between the scales.2-4 The heart is approached from the ventral aspect of the fish. The needle is advanced just caudal to the posterior margin of the bony opercular cavity.4 Advantages include accessibility in a consistent approach and minimal side effects. Disadvantages with these traditional approaches include lack of visualization or palpation of the vessel or heart, lack of multiple access sites for additional attempts, some difficulty in penetrating the thick, mostly scaled integument, mixing of arterial and venous blood,2 and the potential for thrombosis, infection, and hemorrhage.
In the approach presented here, the afferent and efferent vessels of the branchial arch in teleost fish was used to evaluate the ease of sampling and quality of the CBC and select sera chemistries. Twenty fish of five species were sampled in the current study, including largemouth bass (Micropterus salmoides), bluegill (Lepomis cyanellus), white crappie (Pomoxis annularis), green sunfish (Lepomis macrochirus) and sauger (Sauger canadense). Fish were manually restrained after being netted from display tanks. Fish were held in lateral recumbency with dampened vinyl gloves on a dampened plastic liner. The operculum of either the right or left side of the head was abducted and a preheparinized (Heparin, Baxter Healthcare, Deerfield, Illinois, USA) insulin or tuberculin syringe with a 28- or 25-gauge needle was advanced in a plane parallel to the base of the gill arch. In each fish, the vessels were easily observed against the white base of the gill arch. Blood was aspirated and immediately placed into lithium heparinized microtainers (Becton Dickenson, Franklin Lakes, New Jersey, USA) for complete blood counts and select sera chemistries. Gentle pressure at the phlebotomy site assisted hemostasis. In three fish, simultaneous samples were obtained from the coccygeal vessel and branchial vessels of the gill arch. Weights of nine fish ranged from 48 g to 200 g, and up to 2 cc of whole blood was obtained from each fish without any observed untoward effects. Once sampled, fish were returned to a holding tank and consistently observed for 15–30 min, then occasionally over the following 7 days. No hemorrhage or other clinical effects were noted in any fish sampled. Opercular movements were symmetric and hydrodynamics, behavioral grouping, and structure selection were unaltered in the captive fish sampled.
Advantages of the branchial arch vessel technique are ease of access, visualization of the vessels, multiple access sites and apparent lack of side effects, though fish were not physically re-examined. Disadvantages are the potential interference with osmotic regulation, oxygenation, mixing of arterial and venous blood, infection, hematoma or hemorrhage, though none of the latter were observed. Use of preheparinized syringes has the potential for hemodilution and cellular morphology alterations with any of the above techniques, but was elected in these cases to mediate the efficient clotting ability of fish.
This technique may provide the clinical veterinarian, technician, or aquarist additional sites for fish phlebotomy. A larger study to compare and contrast the CBC and select sera chemistries of simultaneous samples from the coccygeal and branchial vessels is underway and involves keeper level staff fishing from two ponds on zoo grounds. This technique is also being evaluated as a means of humane euthanasia for ill fish. Ease of sampling, multiple site access, and lack of apparent complications may provide the clinician with an easier method to obtain blood samples in fish.
The author thanks the Kansas City Zoo staff for their participation and assistance in this project.
1. Ames WE, RM Condie, B Pollara. 1966. A method for intravascular injection and bleeding of fishes. Trans. Am. Fisheries Society. 95: 317–318.
2. Houston AH. 1990. Blood and circulation. In: Schreck CB, PB Moyle, eds. Methods for Fish Biology. American Fisheries Society, Bethesda, Maryland Pp. 277–279.
3. Noga EJ. 2000. Fish Disease: Diagnosis and Treatment. Iowa State University Press, Blackwell Publishing Co., Ames, Iowa. Pp. 26–27.
4. Stoskopf MK. 1993. Clinical examination and procedures. In: Stoskopf MK, ed. Fish Medicine. W.B. Saunders, Philadelphia, Pennsylvania. Pp. 64–65.
5. Whitaker BR. 1999. Preventative programs for fish. In: Fowler ME, RE Miller, eds. Zoo and Wild Animal Medicine, Current Therapy 4. W.B. Saunders, Philadelphia, Pennsylvania. Pp. 179.