Buoyancy disorders of ornamental fish: a review of cases seen in veterinary practice

In veterinary practice, buoyancy disorders are common in goldfish, often having a sudden onset and present floating at the surface or lying on the bottom. Fifty eight affected fish were examined in detail over a period of 11.5 years, of which 47 were goldfish: there were almost equal numbers of short-bodied and long-bodied goldfish. In many cases, there were no external lesions and no consistent environmental factors could be identified. Radiography was performed in 49 fish and proved the most useful investigative approach. Several radiographic abnormalities were found in goldfish including over-inflation (44%), displacement (22%), fluid accumulation (12%) and rupture (2%) of the swim bladder and intestinal tympany (6%). Post mortem and histological examinations were performed on 35 goldfish: findings included systemic granulomatous disease (23%), abnormal fluid in the swim bladder (23%), polycystic kidney disease (17%) and several other internal diseases (20%). However, 17% of goldfish had no identifiable pathology and no consistent radiographic features. Pathological findings in other species were varied and only rupture of the swim bladder in orfe and a renal tumour in oscars were significant. Most cases were euthanased on initial examination due to advanced disease but a quarter were treated conservatively. There was a very poor response to treatment and several environmental, medical and surgical approaches are discussed. In fish, buoyancy is controlled by the amount and distribution of gas within the body. This is primarily enclosed within a gas-filled buoyancy organ, the swim bladder. In some fish, physostomes, there is a patent duct that connects the swim bladder to the anterior oesophagus, which permits air to be swallowed and forced into the swim bladder. In other fish, physoclists, there is no patent connection and the swim bladder is inflated by the release of gas from arterial blood by a vascular rete in the wall of the swim bladder: this also occurs in some physostomes. Lice infestation pressures on farmed Atlantic salmon smolts (Salmo salar Linnaeus) in the west of Ireland following a SLICE® (0.2% emamectin benzoate) treatment PROCEEDINGS Fish Veterinary Journal (2007) (9) 22–37