Abstract

An adult white-spotted filefish presented with the history of difficulty in swallowing food and a distended abdomen. Physical examination revealed a fluid filled abdomen and no obvious problem in the oropharynx. No abnormalities were seen on endoscopic exam of the buccal cavity, esophagus, and stomach. Abdominal tap produced a clear yellow fluid which upon chemical evaluation proved to be urine. The urine contained numerous white blood cells and bacteria. Antibiotic treatment commenced as directed by culture and antibiotic sensitivity results. Initially the animal responded but eventually the problem recurred. Plain radiographs as well as intravenous pyelograms were used to determine if the animal's urinary bladder was intact. A laparoscopy revealed an intact and grossly distended urinary bladder. Subsequent cystocentesis produced aseptic urine with calcium phosphate (carbonate-appetite, 100%) uroliths. Gross necropsy revealed a distended urinary bladder with a thickened wall and inflammation of the mucosal surface of the bladder neck. Histological examination showed foci of calcified material in the epithelium, submucosa and serosal connective tissue of the bladder. Medical and surgical considerations are discussed.

Background, Case Presentation and Initial Workup

The central exhibit at the New England Aquarium is a cylindrical (40'x23'), 60,000 gallon Atlantic coral reef type tank. The exhibit is supplied with natural sea water which is pumped from Boston Harbor. In this semi-closed, recirculating system, heavy particulates are removed via sand filtration while much of the organic waste load is removed through oxidation with ozone.

A varied collection of elasmobranchs, reptiles and teleosts are concurrently on display in this exhibit. Among this collection are 5 white-spotted filefish (Cantherhines macrocerus). The NEAq husbandry staff has been successful in maintaining this species over the past seven years. Recently, the husbandry staff reported that an adult white-spotted file had a decreasing appetite over a two week period, appeared to have difficulty in swallowing food and was beginning to "bloat."

The animal was collected for examination and was anesthetized in a sea water bath with 90ppm tricaine methanesulfonate (MS-222 was successfully used at this concentration for all subsequent diagnostics). Palpation revealed a fluid distended abdomen and abdominocentesis produced a clear yellow fluid. Endoscopic examination of the upper gastrointestinal tract revealed no abnormalities. Radiographs were taken and the animal was returned to exhibit. Subsequent cytological examination of the fluid revealed numerous white blood cells and bacteria were present. The color, odor and initial chemistries of this fluid suggested that it was urine.

Our differential diagnoses at this point included; a ruptured urinary bladder with a septic peritonitis, a distended urinary bladder due to atony or urethral blockage with a urinary tract infection, or a primary peritonitis. The next day an aseptic abdominal tap produced 250ml of fluid. Chemistry evaluation of this fluid was ultimately compared to a subsequent serum sample from this animal (Figure l). The relative values of glucose, BUN, creatinine, calcium, phosphorus, sodium, chloride and the abdominal tap magnesium value strongly suggest that the fluid is urine. Cultures and antibiotic sensitivities (C/S) of the sample were initiated. The animal was placed on intramuscular injections of chloramphenicol (50mg, SID) until antibiotic sensitivity results were available. C/S results showed the growth of an Achromobacter sp. which was sensitive to many antibiotics including tetracyclines. The animal was then placed on intramuscular injections of a long acting oxytetracycline (40mg every third day for 5 treatments). Since ultrasound was unavailable at this time, attempts were made using intravenous pyelography to determine if the urine was contained in an intact bladder. Three ml of REND-M-60(r) (Squibb) stock solution were injected in the caudal vein. Serial radiographs were taken at times 0, l, 3 and l 5 minutes. Although the radiopaque iodide was ultimately visualized in the abdomen, the results were inconclusive.

Figure 1

Case Progression and Subsequent Diagnostics

Approximately five days into the treatment regime, the fish showed an interest in the food and soon began eating well. There was no recurrence of abdominal bloating and animal resumed its normal hours of activities. The animal was asymptomatic for approximately one month when its abdomen again became distended, although its appetite remained. The animal was again anesthetized for abdominocentesis. The same clear yellow fluid was obtained; however, cytological examination and C/S results showed that the fluid was aseptic. Cytological exam also revealed numerous irregularly shaped, globular crystals that sometimes formed a "wheat sheaf" type of arrangement (Figure 2). The crystals were ultimately identified via polarization microscopy supplemented by x-ray diffraction and infrared spectroscopy as being composed of calcium phosphate (100% carbonate apatite).

Since several attempts at retrograde urethral catheterization were unsuccessful, the animals were taken to surgery. Long-term surgical anesthesia was accomplished with the use of a recirculating pump system, [See: A preliminary study of clinical techniques utilized with blue fin tuna (Thunnus thynnus); a comparison of some captive and wild caught blood parameters.] Depth of anesthesia was monitored via electrocardiogram noting heart rate, QRS size and shape changes. Laparoscopic exam revealed a grossly distended urinary bladder nd otherwise normal organ. The diminishing size of the animal's QRS complexes suggested cardiac compromise and made further exploration impossible. The incision site was closed with 2-0 nylon and covered with a layer of nexaband. Recovery from anesthesia was uneventful, however, the fish's coloration did not return to normal and the animal died within two days.

Figure 2

Gross and Histological Pathology

Gross Necropsy

The only significant findings at necropsy were localized within the urinary tract. The urinary bladder was distended (Figure 3) and the wall to be thickened. The bladder contained 200ml of urine with approximately 3g of chalky, cream colored, roughly spherical shaped uroliths ranging 0.001-3.0 mm in diameter. The mucosal surface of the bladder neck appeared inflamed. The inflammation extended 0.5cm into the urethra.

Figure 3

Histological Examination

Histology revealed lesions in the heart, liver, kidney and urinary bladder. The heart contained Mural thrombi and there was extensive fat/glycogen accumulation within the hepatocytes. Some renal tubules appeared dilated and possessed a necrotic epithelium. These epithelial lesions appear to have been anti mortem. In addition numerous granulomata were present within the renal interstitium. The epithelium of the urinary bladder was moderately congested and ulcerated in many areas. Foci of calcified material were seen within the epithelium, submucosal and serosl connective tissue.

Conclusions, Medicaland Surgical Consideration

Mineral deposition within kidney tubules, collecting ducts, ureters of both framed and wild fish has been reported. Nephrocalcinosis is very common in farmed rainbow and brook trout, however, the etiology(ies) remain unknown. This condition has been linked to deficiencies of magnesium, selenium toxicity and high levels of CO_2.^10,12The production of urinary calcium oxalate crystals has been associated with pyridoxine deficiency in trout and vitamin A deficiency in clown fish.⁴ It is presumed that the etiology of nephrocalcinosis is species-specific and, in most cases, dietary in origin.

Calcium phosphate crystal production in small animals is reported to be associated with metabolic disorders such as primary hyperparathyroidism, renal tubular acidosis, and excessive dietary calcium and phosphorus absorption.^3,9 The etiopathogenesis of calcium based uroliths in dogs has been divided into two main categories; hypercalcemic hypercalciuria and normocalcemic hypercalciuiria.³ In hypercalcemic hypercalciuria, the excess serum calcium is filtered and excreted. The resulting hypercalciuria leads to the precipitation of calcium salts. Causes of hypercalcemia in dogs may include primary hyperparathyroidism, pseudohyperparathyroidism, vitamin D intoxication, osteolytic, neoplasia, and hyperparathyroidisim.⁷ In humans, normocalcemic hypercalciuria is associated with either increased intestinal calcium absorption (absorptive calciuria), or decreased renal tubular reabsorption (renal-leak calciuria).⁹

Obviously, there are a multitude of potential primary metabolic disorders or dietary induced situations that can lead to the development of calcium based urinary mineral deposits. Successful treatment is contingent on an understanding of each condition's etiopathogenesis. Treatment of absorptive calciuria is vastly different from the treatment for renal-leak calciuria and an appropriate treatment for one condition could easily exacerbate the other.

The etiology of the urolithiasis in this case is still unknown. The gross necropsy findings of a severely distended bladder and thickened bladder wall suggest the chronicity of the urinary obstruction. It is likely that the animal suffered from a chronic, intermittent obstruction which was ultimately complicated by a bacterial infection. In retrospect, aggressive surgical intervention via cystotomy with thorough ravage and urethral catheterization may have alleviated the obstructive disease. This treatment approach may have only been palliative, however, if the underlying cause was not discovered and corrected. An examination of this animal's conspecific tank mates for comparison with wild caught individuals is planned. The examination will include a comparison of blood chemistries and appropriate hormones, urine parameters and diet composition.

Acknowledgements

The authors would like to thank the Renete Reimschuessel and Andy Kane for their continuing quality support in histological analysis. In addition, we would like to thank the extensive husbandry efforts by the divers of the New England aquarium.

References

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