Abstract

A three-year-old mature male showa koi (Cyprinus carpio) weighing 1,792 g presented in October 1996 to the Veterinary Teaching Hospital of the College of Veterinary Medicine, North Carolina State University (CVM-NCSU) with a two-month history of a distended abdomen. Water quality parameters were within normal limits and the fish had been fed a diet of commercially prepared koi pellets on the fish farm where it lived.

Multiple imaging procedures were performed to characterize the coelomic mass and to localize the organ of origin. Left to right lateral (RL) and right (RDL) and left (LLD) lateral decubital (horizontal beam) whole-body radiographs, caudal coelomic-cavity ultrasonography, and computed tomography (CT) were performed.

The fish was anesthetized for an exploratory celiotomy. Anesthesia was induced by immersing the fish in a 200 mg tricaine methane sulfonate (Finquel®, Argent Chemical Labs, Redmond, WA) solution/L water for five minutes until the fish had only mild opercular movements (the opercula could be observed moving but the motion was not sufficient to generate water flow across the gills). The fish was placed on the surgery area and the delivery tubes of a recirculating anesthesia machine were positioned into its mouth. A stock solution of tricaine methane sulfonate was prepared by dissolving 10 g Finquel® in 1 L of deionized water and buffering it to pH 7.0 with sodium bicarbonate. Anesthesia was maintained with a constant 160 mg/L tricaine methane sulfonate at a flow rate of 3 L/minute for 55 minutes. The concentration of tricaine methane sulfonate was gradually reduced to 38 mg/L over the next 40 minutes as the surgical procedure was completed. Total duration of anesthesia was 100 minutes. The patient was also given a 10 mg/kg intraperitoneal dose of enrofloxacin (Baytril®, Bayer Corp., Shawnee Mission, KS) during surgery to reduce the possibility of a secondary bacterial infection. Butorphanol tartrate (Torbutrol®, Fort Dodge Laboratories, Inc., Fort Dodge, IA) at a dose of 0.1 mg/kg was given subcutaneously at the end of the surgery for pain management.

The scales were removed from the area of the planned incision site with forceps. A ventral midline abdominal incision was made beginning immediately caudal to the base of the pectoral fins and extended to within 1 cm of the cloaca. An osteotome was used to separate the pelvic girdle along its midline. Gelpi perineal retractors were used to maintain retraction of the coelomic incision. A large solid mass was present in the abdominal coelom extending caudally from the liver to the pelvic inlet and was compressing the internal organs dorsally and to the left. Sharp and blunt dissection was used to free the mass from its attachments to the liver, body wall, and kidneys. Larger vessels supplying the mass were divided and ligated using 4-0 polypropylene (Prolene®, Ethicon, Somerville, NJ) suture and bipolar cautery was used to electrocoagulate smaller vascular pedicles. The pelvic osteotomy was repaired using 2-0 stainless steel cerclage wires. The muscle wall was closed with 3-0 polyglyconate (Maxon®, Davis and Geck, Manati, PR) in a simple continuous pattern and the skin was closed with 4-0 polypropylene in a continuous Ford interlocking pattern.

The fish recovered without complication from the anesthesia and surgical procedure. The air space in the coelomic cavity caused the fish to be positively buoyant, thus 110 ml of air was aspirated from the abdomen, correcting the problem. The skin sutures were removed 25 days postoperatively.

Microscopically, the mass was identified as a myosarcoma but could not be morphologically distinguished as a rhabdomyosarcoma or a leiomyosarcoma. Immunohistochemistry and transmission electron microscopy results are pending.

Myosarcomas are not common in fish but have been reported in an African lungfish (Protopterus dolloi) and a cutlass fish (Trichiurus lepturus).^1,2 We found no reports of this tumor in koi or carp, but papillomas, squamous cell carcinomas, and a branchioblastoma have all been described in koi.^4,5

Tricaine methane sulfonate is approved by the Food and Drug Administration (FDA) and is a widely used anesthetic for fish.³ Most fish experience an excitatory stage of anesthesia followed by sedation, a loss of equilibrium, and, finally, a loss of any reactivity. It is desirable to maintain an anesthetic plane at this level. Mild opercular movements should be maintained and the gills must be bathed sufficiently with anesthetic water. Anesthetic effects of tricaine methane sulfonate are quickly reversed by diluting the concentration and placing the fish into a solution of fresh, clean water.

The surgical removal of this tumor relieved unnatural pressure on the internal organs and the body wall. The fish appeared clinically normal six months after the procedure.

Acknowledgments

The authors thank Drs. Michael Stoskopf and Craig Harms for their assistance with case management.

Literature Cited

1.  Endo M. Spontaneous tumors in the cutlass fish Trichiurus lepturus and the dusky spinefoot Siganus fuscescens. Japanese J Ichthyology. 1991;37(4):421–423.

2.  Hubbard GB. A seminoma and a leiomyosarcoma in an albino African lungfish (Protopterus dolloi). J Wildl Dis. 1985;21(1):72–74.

3.  Stoskopf MK. Anesthesia of pet fishes. In: Kirk, Bonagura, eds. Current Veterinary Therapy XII. WB Saunders Co; 1995:1365–1369.

4.  Wildgoose WH. Papilloma and squamous cell carcinoma in koi carp (Cyprinus carpio). Vet Record. 1992;130:153–157.

5.  Wildgoose WH, Bucke D. Spontaneous branchioblastoma in a koi carp (Cyprinus carpio). Vet Record. 1995;136:418–419.