Elevated blood urea nitrogen (BUN) levels in goldfish as an indicator of gill dysfunction

We examined the effects of copper-induced gill proliferation and gentamicin -induced renal tubular injury on serum creatinine and blood urea nitrogen ( BUN) in goldfish Carassius auratus. Fish were given intraperitoneal injecti ons of gentamicin or phospate-buffered saline and kept in either freshwater or copper-treated (100 mu g/L) water. Those fish injected with gentamicin showed histologic signs of tubular necrosis. The copper-treated fish had ex tensive gill epithelial cell hypertrophy and hyperplasia. Serum BUN levels were significantly higher in copper-exposed fish than in freshwater fish, r egardless of gentamicin treatment. Serum creatinine levels were unchanged b y any of the treatments. This indicates that excretion of nitrogenous waste s across gill membranes is an important part of endogenous toxin removal. H owever, creatinine serum levels are apparently unaffected by either gill da mage or kidney failure. Elevated BUN levels in teleosts may serve as a clin ical indication of respiratory and excretory compromise due to respiratory epithelial cell hypertrophy and hyperplasia.