Renal Cystic Adenocarcinoma in a Flowerhorn Cichlid with Metastatic Involvement of the Spleen

Renal Disease in Teleost Patients

The number of fish as pets far exceeds the populations of any other companion animal. As our knowledge of aquatic animal species and aquatic animal medicine continues to expand, veterinary expertise is becoming more critical to the client, researcher, fisheries biologist, aquarist, farmer, and fish hobbyist. Similar to other vertebrates, fish are susceptible to infectious and noninfectious renal disease. This article compares vertebrate renal anatomy and physiology and highlights some renal disease examples.

Putative histiocytic sarcoma in redfin needlefish Strongylura notata (Beloniformes: Belonidae) in Florida, USA

Redfin needlefish Strongylura notata from Florida coastal waters were observed with unusual neoplastic lesions. Affected specimens were collected from 1 Atlantic estuary (Indian River Lagoon, prevalence = 0.32%, n = 5314) and 2 Gulf of Mexico estuaries (Tampa Bay, prevalence = 0.02%, n = 10762; Charlotte Harbor, prevalence = 0.02%, n = 5112) during routine fisheries-independent monitoring surveys conducted from 1999-2009. Grossly, each lesion manifested as a large (18-30 mm × 20-50 mm), raised (approximately 10 mm), white, creamy, or pinkish nodule on the flank, dorsal trunk, base of the pectoral fin, or head. Multiple small (<5 mm) nodules possessing poorly demarcated borders with neighboring tissues on the external jaw surface and at the base of the teeth were also observed. Histopathologically, neoplastic cells were found in the dermis, beneath the skeletal muscle, and in the soft tissue at the base of teeth of the premaxilla and the dentary jaw processes. Neoplastic cells usually had prominently invaded among the myosepta of the skeletal muscle. Neoplastic parenchymal cells had the basic characteristics of atypical, mononuclear, round, histiocytic cells with an eccentric, reniform nucleus and abundant cytoplasmic vacuolation, while some exhibited bizarre nuclear pleomorphism. Transmission electron microscopy revealed that neoplastic cells had a grooved nucleus and cytoplasmic organelles with rough endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes. Neoplastic cells had possibly metastasized to liver, spleen, and kidney. Positive immunohistochemical staining with Ki67, p53, S-100, and CD163 support neoplastic features and a putative diagnosis of histiocytic sarcoma.