Abstract

A superficial biopsy of an ulcerated mass on the right caudal lateral body was taken from a 5 kilogram largemouth bass (Micropterus salmoides) and histologically diagnosed as a locally invasive soft tissue sarcoma with low probability of metastasis. An on-site evaluation of the fish revealed a good surgical candidate that had an adequate body condition, normal appetite and activity level, with an alert, responsive demeanor. A 3 centimeter by 5 centimeter ovoid, elevated, ulcerated mass was protruding from the right caudal lateral body. A treatment plan was devised using surgical excision and cryotherapy to remove the tumor was planned.

Intraoperative anesthesia and analgesia were performed using a fish anesthesia system composed of a MS-222 induction bath, injectable butorphanol, a lidocaine field block, and a maintenance flow of MS-222-treated water with supplemental oxygen. The surgical site was prepared by removing a 1.5 centimeter zone of scales circumferentially around the mass.

The ulcerated mass including a one centimeter margin on all planes was excised via standard and electrosurgical techniques. Dermal hooks made out of 25-gauge hypodermic needles were employed to hold and elevate the mass during excision. Hemorrhage was controlled initially using pressure, vascular occlusion via hemostats, and electrocautery. As insufficient margins were expected based on location and tumor type, cryotherapy^1,2,3 was performed using both liquid nitrogen^{1, 2} and nitrous oxide with the goal of freezing an extra 0.5 to 1.0 centimeter at the surgical margin. The cryotherapy also aided in surgical site hemostasis. The 5 centimeter by 7 centimeter by 1 centimeter deep ovoid wound was left open to heal by secondary intention. A gel bandage⁴ of 0.0024% misoprostol and 2% phenytoin was applied in a thin layer to act as a barrier to aid in appropriate osmoregulation and to stimulate wound healing. The fish recovered without event after returning to the 200 gallon holding pool.

The excised mass was bread loafed at 1 centimeter intervals and subsequently fixed in 10% buffered formalin for histopathological assessment of margins. The presence of a dermal soft tissue sarcoma with secondary bacterial infiltration was confirmed. In addition, neoplastic spindle cells were observed extending to the surgical margins.

Post-surgical care consisted of reapplication of the gel bandage every 3 days, administration of meloxicam and enrofloxacin, and assisted feeding. Tissue frozen during cryotherapy sloughed off the wound over a 14 day post-operative period and was followed by development of healthy granulation tissue. An additional course of ceftazidime was administered during granulation tissue development. Healing progression was observed with filling in of the wound from the bottom out with fibrotic tissue and the slow epithelialization of the wound.

Acknowledgements

The authors would like to thank Bass Pro Corporate for allowing us the opportunity to go the extra mile for Nakoma and to Melanie Roberts for assisting in the surgery and providing post op care.

* Presenting author

Literature Cited

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