A spontaneous neoplasm of the renal collecting ducts in an oscar, Astronotus ocellatus (Cuvier), with comments on similar cases in this species

Abstract

A 25 cm adult oscar, Astronotus ocellatus (Cuvier), older than 5 years with abnormal behaviour, abdominal distension and general deterioration of body condition was received from a private owner for evaluation and treatment. The oscar bad been kept in a 200L aquarium, shared with a plecostomus catfish. Water quality parameters were maintained within normal limits for this freshwater tropical cicblid. It had been healthy for years when its condition began to deterio-rate, and abdominal distension became noticeable about 3 months before death.The owner first took the fish to the local pet store and was advised to withhold food for 2 weeks, but this produced no improvement. Lethargy and debilitation progressed, and it began to list over time. When presented to the laboratory for clinical evaluation, 60 mm of dark brown, serosanguinous transudate was aspirated from the caudoventral abdomen. Treatment consisted of the broad spectrum antibiotic chloramphenicol at a dose of 50 mg kg"' i.m. and the an ti-inflammatory drug dexamethasone at a dose of 2.0 mg kg"' i.m. Despite these measures, the fish died approximately 12 h after presentation. Necropsy revealed an enlarged, polycystic posterior kidney, while all other internal organs appeared grossly normal.Sections of the kidney, heart, liver, spleen and stomach were routinely prepared for histology. The posterior kidney sections consisted of multiple

Occurrence of spontaneous tumours of the renal proximal tubules in oscars Astronotus ocellatus

“…Primary neoplasms of the kidney are rarely described in fish in the literature (Huizinga & Budd 1983, Lee et al 1989, Petervary et al 1996, Wildgoose 2001. The most common renal neoplasms in fish are nephroblastomas, which can be chemically induced or develop spontaneously and have been reported in trout and other commercially farmed fish species (Huizinga & Budd 1983, Lee et al 1989, Bailey et al 1996, Baumann & Okihiro 2000, Lumsden & Marshall 2003.…”

“…The first report of a renal neoplasm in an oscar in the USA was in 1996 (Petervary et al 1996) but a definitive classification of this tumour was not given. The differential diagnoses based on histological findings included cystadenoma or adenocarcinoma of either the renal tubules, the collecting ducts, the mesonephric duct or the thyroid.…”

“…The differential diagnoses based on histological findings included cystadenoma or adenocarcinoma of either the renal tubules, the collecting ducts, the mesonephric duct or the thyroid. Petervary et al (1996) had the opportunity to review material on a further 3 cases from the Registry of Tumours of Lower Animals at the Smithsonian Institution (Washington, DC) that had remarkable histological similarities to their case. Later, these neoplasms were classified as urinary bladder tumours (Harshbarger & Slatic 2001).…”

“…In 2004, another renal tumour, a papillary cystic adenoma, was de-scribed in an oscar (Gumpenberger et al 2004), and histological findings suggested that this originated from the proximal tubules of the kidney. Although all these tumours were fairly well differentiated and only occasionally invaded adjacent tissue, the fish were killed due to the severity of clinical signs resulting from the tumours' expansive growth, compression of adjacent organs and disturbance of normal kidney function (Petervary et al 1996, Gumpenberger et al 2004). Metastases were not found in any of these cases.…”

“…These tumours were compared histologically to material from the case described by Petervary et al (1996). In addition, material from 4 of the 5 cases was examined using electron microscopy.…”