Surgery in Fish
World Small Animal Veterinary Association World Congress Proceedings, 2015
Nick Saint-Erne1, DVM, CertAqV
1Technical Service Veterinarian, PetSmart, Inc., Phoenix, AZ, USA

Learning Objectives

After anesthesia is administered, several surgical procedures can be performed on ornamental fish, including laceration and fin tear repairs, biopsies, mass removals, resection of prolapsed intestines, fracture repair, and abdominal surgery to remove impactions and tumors.

In ornamental fish, especially large species such as koi or fish on display in a public aquarium, the value of the fish will often make it desirable for clients to seek veterinary care for their fish. Surgery can be performed on ornamental fish in a veterinary hospital with equipment and anesthetics veterinarians likely already have in their clinics. General surgical knowledge and experience will facilitate successful fish surgery, as will familiarity with normal fish anatomy. Frequently, these are surgeries for external skin or fin tumor excisions and abdominal exploratory surgeries to remove masses or biopsy organs. Other surgical procedures have been performed for repair of lacerations from traumatic injuries, resection of prolapsed cloacal tissues, and orthopedic procedures on fish with spinal fractures.

After the fish is in an adequate plane of anesthesia [See Anesthesiology in Fish, it is removed from the anesthetic solution and placed on a wet chamois cloth, towel or foam in the appropriate position for surgery. Rolled-up wet towels or foam wedges can be placed on either side of the body to maintain the fish in dorsal recumbency if that is the desired position. Exposed tissues not in the surgical field are covered with wet cloth to prevent desiccation. Ophthalmic ointment should be placed on the eyes to keep them moist.

The surgical site is gently cleaned with a 1:10 diluted solution of 1% povidone-iodine (Betadine) in 0.9% physiological saline. A clear plastic surgical drape can be placed over the surgery site; small dabs of petroleum jelly (Vaseline) will help it adhere to the skin. The aerated anesthetic solution is dripped over the gills to maintain anesthesia, or plastic tubing can be placed into the fish's mouth and the solution slowly pumped in and across the gills. The anesthetic solution flow can be maintained via a motorized pump such as an aquarium powerhead, by gravity using an IV bag and drip set filled with the anesthetic solution, or by hand with a syringe attached to IV tubing or aquarium air line.

The best surgical instruments for fish surgery are ophthalmic or microsurgery instruments because of their small size; but many surgeries can be performed with a scalpel with a #11 or #15 blade, iris scissors, Metzenbaum scissors, mosquito hemostats, and a pair of fine forceps. A jeweler's loupe or other magnifying lens is very helpful.

Abdominal surgery is performed in large fish such as koi through a ventral midline incision. Start the incision cranial to the vent and continue forward to the pectoral fin bones, as needed. Scales along the incision may be cut through or removed with forceps prior to making the incision. I prefer to leave the scales in place until cut with scissors while making the midline incision and then remove the damaged scales, rather than pre-plucking the scales along the surgical site. The former method tends to not remove as many scales from the fish as the latter, reducing trauma to the epithelium and dermis. The latter method makes cutting through the skin easier in heavily scaled fish species. The pelvic girdle may be separated with Mayo scissors or bone cutters if necessary.

Use gentle blunt dissection with the hemostats, Metzenbaum scissors, or gloved fingers to isolate the desired tissues. Ligate blood vessels as needed with 3-0 or smaller absorbable suture material such as Vicryl or Maxon. Stainless steel Hemoclips may also be used for ligation. Bipolar cautery units are useful for small vessel hemostasis.

Successful abdominal surgeries have been performed on koi (Cyprinus carpio) to remove both testicular and ovarian gonadal tumors. These appear as large (as much as 10% of the total body weight in size), irregular, fibrous masses in the caudal abdomen. They often cause the abdomen to appear quite distended. These can be bluntly dissected free from fibrous attachments, using appropriate hemostasis. After removal, survey the abdominal organs to assess any damage from pressure necrosis or obstruction. The contralateral gonad should also be assessed.

Occasionally a fish's gas bladder will become traumatized and distended, creating an appearance similar to an abdominal tumor. A radiograph or ultrasound examination will distinguish between an enlarged gas bladder and a tumor. The gas bladder in koi and goldfish consists of two compartments joined by an isthmus. The caudal compartment is connected to the esophagus by the pneumatic duct. The damaged compartment of the gas bladder can be isolated and ligated for removal. The cranial compartment when removed is ligated at the isthmus. The caudal compartment is ligated distal to the pneumatic duct, leaving it attached to a remnant of the caudal compartment near the isthmus. The fish will gradually stabilize its buoyancy with the remaining portion of the gas bladder.

Muscle layers can be closed with absorbable suture material in a simple continuous suture pattern. Trapped air in the abdomen should be removed by filling the abdomen with sterile saline solution to displace any air, then use suction while closing the muscles and before closing the skin. In smaller fish, the muscle layer and skin may be closed in one layer. For skin closure use small monofilament nylon suture material with a swaged-on reverse cutting needle. Simple continuous or simple interrupted suture patterns are most often used to oppose the margins of the skin incision. Remove the skin sutures in 2–3 weeks, or when the skin appears adequately healed.

Skin and fin wounds can be sutured using fine (3-0) monofilament nylon sutures. To repair split fin membranes, gently scrape the opposing edges with a scalpel blade to remove scar tissue (if not a fresh injury), and then tightly oppose the fin edges with a series of simple interrupted sutures or a continuous suture pattern [Figures 1-3] (VIN editor: Figures were not provided at the time of publication). Start at the base of the tear, and work outward toward the edge of the fin. Incorporate one or more fin rays in each side to keep the suture from tearing through the fin membrane. Apply topical disinfectant (e.g., Betadine) solution to the fin before and after suturing. Remove the sutures in 3 weeks. Hyperplasia of the epidermis will grow over the suture sites, but will regress after the sutures are removed, and it can be trimmed back at the time of suture removal.

Scale injuries from netting or handling can also be repaired if the sloughed scale still contains adequate attached epidermis, and is immediately replaced in its normal position. Hold the scale in place with a few small simple interrupted sutures through the surrounding tissue. Clean the skin with topical iodine solution. Remove the sutures in 7 days, or when the tissue has reattached.

During a surgical procedure, an electrocardiogram (ECG) reading can be taken to monitor the heart rate and rhythm. Three ECG lead clips can each be attached to the metal part of 22-gauge hypodermic needles. These needles then are placed through the skin and into the muscle tissue at the base of the right pectoral fin (RA lead), the left pectoral fin (LA lead), and cranial to the vent opening (LL lead). The P-QRS-T waves produced are of low amplitude (1 mV QRS complex), but similar to those in other animals. Heart rates are temperature dependent, as well as being affected by anesthesia. Typical heart rates are 30–40 beats per minute, but can range from 15 to 100 beats per minute, depending on species. The pulse rate will decrease as the koi is more anesthetized, so the pulse rate can be used to judge the depth of anesthesia. Increase fresh water flow across the gills to lessen the anesthesia and cause the pulse to increase if it slows too much.

After surgery, place the fish in aerated non-anesthetized water of the same temperature in a recovery tank with dim lighting, in a quiet area, with a cover to prevent jumping. Post-surgical butorphanol can be administered to control pain at 0.1–0.4 mg/kg IM. Tube feed fish food made into gruel in a blender if the fish is not eating by the day after surgery. Surgical success depends on condition of the fish prior to surgery, adequate surgical correction of problem, good hemostasis, proper incision closure, bacterial prevention, and good water quality.


1.  Roberts H. Surgery and wound management in fish. In: Fundamentals of Ornamental Fish Health. Ames, IA: Wiley-Blackwell; 2010.

2.  Saint-Erne N. Advanced Koi Care. 2nd ed. Glendale, AZ: Erne Enterprises; 2010.


Speaker Information
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Nick Saint-Erne, DVM, CertAqV
PetSmart, Inc.
Phoenix, AZ, USA