Nephroblastoma in a Koi (Cyprinus carpio)

A cachexic 2-year-old koi (Cyprinus carpio) presented with progressive distension of the coelom (1-month period) and anorexia of 2 days' duration. The fish had been maintaining a normal swimming position, although it was often observed low in the water column. Water quality was within normal limits. A skin scrape, fin clip, and gill clip were unremarkable. The respiration rate (opercular movement) was elevated at 100 breaths per minute. Blood chemistry values demonstrated a hypoalbuminemia (1.3 g/dL), elevated uric acid (1.3 mg/dL), elevated creatine kinase (>14,000 U/L), and hyperkalemia (3.9 mmol/L). Ultrasound revealed a fluid-filled coelom and a soft tissue mass containing large vessels filling most of the coelomic cavity. Fine-needle aspirates of the mass were nondiagnostic, though a poorly exfoliating mesenchymal tumor was suspected. The mass was surgically excised. Pathological examination of the mass revealed it to be a poorly demarcated and unencapsulated neoplasm forming 3 histological patterns in which a spindle cell stromal component predominated over an intermediate-sized blastema and much smaller tubular patterns. These features were most consistent with a nephroblastoma. The koi survived 5 days postoperatively but remained low in the water column and was found dead on day 6. A full necropsy of this patient was not performed.