Surgical removal of a seminoma from a black sea bass

Surgical removal of a seminoma from a black sea bass Chick Weisse, VMD; E. Scott Weber, MSc, VMD; Zach Matzkin, VMD; Alan Klide, VMD, DACVA

' Fish can develop abdominal swellings for various reasons, including neoplasia, abscess, granuloma, egg retention, problems in ovipositioning, hematoma, swim bladder abnormality, ascites, or foreign body. ' Diagnostic techniques such as survey radiography, positive-contrast radiography, and computed tomography can aid in identifying the underlying cause. ' In certain circumstances, general anesthesia and surgery can be performed safely in fish.

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n adult black sea bass (Centropristis striata) was evaluated in December of 2000 because of abdominal distention and a decreased appetite. The fish was wild-caught prior to the summer of 1999. This species is added regularly to the New Jersey State Aquarium’s 760,000-gallon Ocean Tank display, and individuals are not tagged. Unfortunately, quarantine records were not available. Ocean Tank conditions consisted of artificial seawater mix at a salinity of 34 parts per thousand with ozonation and sand filtration at 69 F and chronically high nitrates at approximately 80 µg/g (parts per million). The fish was acclimated to the ocean tank exhibit and proceeded to grow well on a diet of cut capelin (Mallotus villosus) and game fish chow.a The fish did not have clinical signs of disease while in captivity until approximately 6 weeks prior to evaluation when the sea bass developed bilateral abdominal distention and separated itself from the other black sea bass. The fish was removed from the exhibit and placed in a quarantined holding tank for observation. The holding tank maintained optimal seawater conditions, using the same artificial seawater mixture at a salinity of 34 parts per thousand and a temperature of 74 F. On physical examination, the fish weighed 2,365 g and measured 35.56 cm in total length. All fins were frayed, and petechia was noticed at the fin bases. A large abdominal swelling was evident that was firm on palpation. The fish had bilaterally atrophied musculature along the spine but no other external abnormalities. Differentials for this abdominal mass included neoplasia, abscess or granuloma, egg-retention, problems in ovipositioning, hematoma, swim bladder abnormality, ascites, or foreign body. While in the holding tank, the fish remained anorectic despite being offered various foods.

From the Sections of Small Animal Surgery (Weisse), Epidemiology and Public Health (Matzkin), and Critical Care (Klide), Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104-6010; and the New England Aquarium, Central Wharf, Boston, MA 02110-3399 (Weber). Address correspondence to Dr. Weisse. 280

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Diagnostic testing included survey radiography, positive-contrast radiography, and computed tomography (CT). Lateral and ventrodorsal radiographic views were obtained while the fish was under anesthesia (200 mg/L tricaineb buffered with equal weight of sodium bicarbonate) and indicated the presence of a primarily left-sided caudoventral abdominal soft tissue mass compressing the swim bladder (Fig 1). A CT scanc confirmed the large abdominal mass compressing the internal organs craniad. Density measurements of the mass ranged between 40 and 50 Hounsfield units, indicating the mass was a soft tissue density and not a fluid-filled cystic structure. Six milliliters of a dilute oral contrast agent (3 ml iohexol,d 3 ml water) was administered via orogastric tube to determine whether the mass was of gastrointestinal origin. Repeat CT revealed a contrast-filled stomach and confirmed a left-sided gastric compression and flattening of the ventral surface of the swim bladder (Fig 2). To avoid the time necessary for progression of contrast through the intestine, a barium enema was performed. Ten milliliters of a 50% barium solution was administered via a lubricated 10-F red rubber catheter passed through the anus. Lateral and ventrodorsal radiographic views were obtained immediately, and these indicated unhindered passage of contrast throughout the gastrointestinal tract (Fig 3). The mass was therefore unlikely to be of gastrointestinal origin, and because of its caudoventral location, a gonadal tumor was suspected. Exploratory surgery was elected and performed 2 weeks later. The sea bass was anesthetized with tricaine methanesulfonate.b The fish was induced in holding tank water with 200 mg/L tricaine buffered with an equal weight of sodium bicarbonate. The water was aerated with an air stone. After 2 minutes the fish rolled over laterally, and after 4 minutes it was removed from the induction container and placed on a combi-

Figure 1—Lateral radiographic view of an abdominal soft tissue mass (M) in a sea bass. The swim bladder (S) is located craniodorsally. JAVMA, Vol 221, No. 2, July 15, 2002

Figure 4—Photograph of a combination fish anesthesia machine-surgery table. A = Tanks with seawater with 2 concentrations of tricaine.b B = Tank with seawater only. C = Air stones. D = Powerheade connected to tubing. E = Inflow tubing carrying water toward the fish. F = Valve that controls the flow of water. G = Inflow tubing sized to fit into fish’s mouth. H = Outflow drain carrying water from table top back into tank of origin. X = Trough for positioning fish.

Figure 2—Axial computed tomography image of the abdominal mass (M) of the fish in Figure 1, compressing the contrast-filled stomach.

nation fish anesthesia machine-surgery table (FAMST; Fig 4). The FAMST was designed and built by 1 of the authors (ZM). The machine consists of a cart with 2 shelves. The bottom shelf holds 3 tanks, each of which contains an air stone and any 1 of which can hold a moveable submersible water pump.e Water is pumped through plastic tubing up to the surgery table on the top shelf. The acrylic surgery table was designed with an adjustable central trough to accommodate different size fish in a variety of positions. Water passes through the fish’s mouth, out over the gills, and through holes in the surgery table and is collected beneath to drain into the tank containing the water pump. One tank contains water without anesthetic, and the other 2 tanks have different anesthetic concentrations that are chosen on the basis of the JAVMA, Vol 221, No. 2, July 15, 2002

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Figure 3—Lateral radiographic view of the fish in Figure 1 following barium enema. The abdominal mass (M) is compressing the contrast-filled gastrointestinal tract dorsally and cranially.

physical condition of the fish, the species, and the fish’s responses to the anesthetic. The submersible water pumpe and drainpipe are moved together between tanks according to the fish’s depth of anesthesia. In our fish, the initial concentration of tricaine administered from the FAMST was 100 mg/L. The concentration of tricaine was changed from 100 to 130 to 115 mg/L depending on the signs of depth of anesthesia over the duration of the 80-minute procedure. Following anesthesia induction, the fish was placed in dorsal recumbency and passively secured in place in the trough of the FAMST. A small bead of sterile lubricating jelly was placed bilaterally, approximately 1 cm lateral of midline, extending from the pelvic fins to the anus. A sterile clear drapef with small aperature was placed and secured by the lubricating jelly and adherence to the moist surface of the fish. The protective mucus covering of the fish was minimally disrupted by careful removal of scales along the ventral midline from the pelvic fins to 0.5 cm cranial to the anus. An 11-cm ventral midline abdominal incision revealed the descending intestines closely adhered to the irregular, tan-pink, red and brown, and bulging abdominal mass. The mass was gently dissected both sharply and bluntly, and several 2to 3-mm-diameter contributing vessels required surgical ligation with size 4-0 polydioxanone.g Following removal of the mass, abdominal exploration revealed no evidence of active hemorrhage or compromise to any of the abdominal viscera. The lack of abdominal musculature precluded the use of any subcutaneous suturing. The incision was closed in 1 layer with size 3-0 nylonh in a continuous Ford interlocking pattern. Prior to complete closure, an 18-gauge catheter was placed through the incision, and approximately 50 ml of free abdominal air was removed to help minimize postoperative positive buoyancy problems. The excised mass weighed 396 g. Heart rate was monitored by use of an ECG,i a

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Doppler flow probe,j and a pulse oximeter.k The heart rate varied between 60 and 80 beats/min over the anesthetic time. The electrodes for the ECGi were connected to hypodermic needles placed subcutaneously: 1 needle on each side between the branchiostegal membrane and the pectoral fins and 1 needle approximately 25 mm caudal to the anal fin slightly paramedian on the left side. The monitor was set to record lead II. A ground wire was run from the ECG machine into the water that was flowing through the fish. The electrocardiogram was not consistent, but regular ventricular complexes could be seen although the baseline was not stable and there was considerable artifact. The Doppler ultrasonic flow probej well was filled with aqueous coupling gel and manually held in position intermittently on the dorsal surface of the tongue. Hemoglobin saturation (Spo2) was monitored with a pulse oximeterk by use of a transmittance lingual clip sensork placed on a pectoral fin and a reflectance rectal sensork placed on the dorsal midline region of the tongue. The Spo2 varied between 52 and 74%. The respiratory rate was 11 opercular movements/min initially; 11 minutes into the procedure, the only ventilatory motion was movement of the branchiostegal membrane, which reached 60 movements/min. The ventilatory movements stopped for the remainder of the procedure. Following surgery, the fish was placed in holding tank water without anesthetic, and within 6 minutes the ventilatory rate was 32 opercular movements/min. After surgery, the fish recovered in the holding tank without complications but remained anorectic for 5 days. Nutritional support was deemed necessary at this point. The fish was anesthetized as for the radiographic procedures, weighed, and tube fed 30 ml of gel food slurry less the gelatin. The following day the fish began to eat thawed mussels. During the following week, its appetite improved dramatically, and normal food intake resumed. Five weeks after surgery, the fish was anesthetized for suture removal. The incision had healed well, and much of the continuous suture material was hanging loose from the skin. Radiography was repeated 8 weeks after surgery and revealed no evidence of mass regrowth at that time. All fins healed, and the musculature along the dorsal spine had begun to redevelop. Histologic evaluation of the mass revealed it was multilobular, partially encapsulated, and highly cellular, with nests of eosinophilic cells invading the interstitial spaces between seminiferous tubules containing spermatids or spermatozoa. The eosinophilic cells were large and round with large vesicular nuclei containing large solitary round nucleoli. There was considerable anisokaryosis, and mitotic figures numbered 0 to 1/high power field. Histopathologic findings were consistent with a seminoma (Fig 5). Use of radiography and CT in fish has been previously reported.1-5 Both diagnostic modalities were useful for identification of a mass in the abdominal cavity in our fish, but only the positive contrast radiography helped confirm that this mass was not of gastrointestinal origin. Upper gastrointestinal positive contrast studies have been described; however, 1 study1 (in a 282

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Figure 5—Photomicrograph of a section of abdominal mass from the fish in Figure 1 revealing large round eosinophilic cells with marked anisokaryosis and mitotic figures numbering 0 to 1/high power field. These histopathologic characteristics are consistent with a seminoma. H&E stain; bar = 24.7 µm.

gourami) reported 90 minutes’ duration before the contrast agent had passed sufficiently for a diagnostic study with intestinal contrast filling from the stomach to the anus. Carnivorous fish such as black sea bass have relatively short gastrointestinal tracts. This characteristic allows easy contrast filling of the entire length of the gastrointestinal tract following barium enema. Captive reproduction problems in finfish are most commonly associated with environmental factors that affect water quality, lighting and photoperiod, and nutrition.6 In addition, some natural deaths of fish in collections at various aquariums and fish farms have revealed ovarian infections associated with peritonitis. It is also recognized that eggs of many finfish species will ripen and overripen but will not be oviposited in captivity; however, thorough pathologic investigations of individual fish retaining large overripened egg masses have not been performed.7 Black sea bass have dimorphic sexual characteristics, and this fish appeared phenotypically male. Therefore, egg retention may be thought improbable, but this remained a differential diagnosis, as black sea bass are protogynous hermaphrodites, changing from female to male. There is also the theoretical possibility that an ovarian tumor could produce excess male hormones, resulting in a male phenotype. Swim bladder abnormality, ascites, and foreign body were easily ruled out by use of the diagnostic methods described. Foreign bodies may be considered an unlikely or unusual differential, but in exhibits that have openings to the public, some specimens with masses or buoyancy problems have had small toy items recovered from the stomach or intestines. An abdominal hematoma has been reported in a gourami, but the history described sudden rapid abdominal distention.1 This sea bass had a slow progressive history of asymmetrical abdominal distention. Although surgical procedures are performed more commonly on fish in the research arena, a few reports1-4,8,9 of clinical surgical cases have been described. This case supports the conclusions of those previous reports that JAVMA, Vol 221, No. 2, July 15, 2002

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Mazuri, PMI Nutrition International Inc, Brentwood, Mo. Tricaine methanesulfonate, Finquel, Argent Chemical Laboratories, Redmond, Wash.

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ProSpeed CT with helical capabilities, General Electric Inc, Madison, Wis. d Iohexol, Omnipaque, Nycomed Inc, Princeton, NJ. e Hagen Aquaclear 402 Powerhead, Rolf C Hagen (USA) Corp, Mansfield, Mass. f Steri-drape, 3M Health Care, St Paul, Minn. g PDS, Ethicon Inc, Somerville, NJ. h Ethilon, Ethicon Inc, Somerville, NJ. i Escort II, 100 series, modular patient monitor, Arleta, Calif. j Doppler ultrasonic Doppler flow detector, model 811 series, probe frequency 9.4 MHz, Parks Medical Electronics, Aloha, Ore. k Palco oximeter model 340, lingual clip sensor, and rectal sensor with temperature, Palco Labs, Santa Cruz, Calif.

References 1. Harms CA, Bakal RS, Khoo LH, et al. Microsurgical excision of an abdominal mass in a gourami. J Am Vet Med Assoc 1995;207: 1215–1217. 2. Lewbart GA, Stone EA, Love NE. Pneumocystectomy in a Midas cichlid. J Am Vet Med Assoc 1995;207:319–321. 3. Lewbart GA, Spodnick G, Barlow N, et al. Surgical removal of an undifferentiated abdominal sarcoma from a koi carp (Cyprinus carpio). Vet Rec 1998;143:556–558. 4. Harms CA, Lewbart GA. Surgery in fish. In: Bennett RA, ed. Vet Clin North Am Exotic Anim Pract 2000;3:759–774. 5. Stoskopf MK. Surgery. In: Stoskopf MK, ed. Fish medicine. Philadelphia: WB Saunders Co, 1993;91–97. 6. Bromage NR. Broodstock management and seed quality— general considerations. In: Bromage NR, Roberts RJ, eds. Broodstock management and egg and larval quality. Oxford, UK: Blackwell Science Ltd, 1995;1–25. 7. Bromage NR, Bruce M, Basavaraja N, et al. Egg quality determinants in finfish: the role of overripening with special reference to the timing of stripping in Atlantic halibut Hippoglossus hippoglossus. J World Aquaculture Soc 1994;25:13–21. 8. Probasco D, Noga EJ, Marcellin D, et al. Dermal fibrosarcoma in a goldfish; case report. J Small Exotic Anim Med 1994;2: 173–175. 9. Nadelstein B, Bakal R, Lewbart GA. Orbital exenteration and placement of a prosthesis in fish. J Am Vet Med Assoc 1997;211:603–606. 10. Wagner GN, Stevens ED, Harvey-Clark C. Wound healing in rainbow trout following surgical site preparation with a povidoneiodine antiseptic. J Aquatic Anim Health 1999;11:373–382. 11. Harshbarger JC. Registry of tumors in lower animals supplement. In: Registry of tumors in lower animals. Washington, DC: Smithsonian Institute, 1965–1981. 12. Masahito P, Ishikawa T, Takayama S. Spontaneous spermatocytic seminoma in African lungfish. J Fish Dis 1984;7:169–172.

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certain surgical procedures can be performed safely in fish. While basic surgical techniques can be extrapolated for use in fish, certain important differences exist. The close proximity of running water, incompletely sterile surgical fields, and the general immobility of most fish skin can complicate otherwise simple procedures. Sterile preparation of surgical fields has been described elsewhere in fish but was not performed in this case to spare the protective mucus covering of the sea bass. At least 1 study10 identified no difference in wound healing complications among rainbow trout with pre- and postsurgical topical povidone-iodine antiseptic preparation versus those surgical incisions in which topical antiseptic treatment was not used. Large clear transparent plastic drapes without adhesive appear to be the most useful for isolation of the surgical field. These drapes tend to adhere to the lubricating jelly and moist surface of the fish and, therefore, become secured in place. These drapes also help maintain moisture and thus reduce desiccation of the skin surface. The small size of many fish as well as the presence of scales often precludes the use of towel clamps for anchoring the drapes. Hemostasis was a critical concern in this fish because of the highly vascularized neoplasia and the absence of vascular access and replacement fluids or blood products. Vascular catheterization in fish is technically complicated and was therefore not performed in this fish. There is also a paucity of information available concerning the appropriate formulation for replacement crystalloids in fish. Tumors of the male reproductive tract of fish have been described and include seminomas, leiomyomas, Sertoli cell tumors, Leydig cell tumors, and epizootic testicular tumors.11 The seminomas that have been reported were found in an African lungfish and a thornback skate.11,12