Ornamental Fish Q&A 17

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A group of goldfish were purchased. Because construction of their pond had not been completed, the owner elected to house them in galvanized steel tanks that he borrowed from a friend. After three days the fish began to die.

Water quality parameters were as follows:

Dissolved oxygen: 7.0 p.p.m.

Total ammonia nitrogen: 3.0 p.p.m.

Temperature: 26°C (78.8°F)

Nitrite: 0.5 p.p.m.

A fish that had just died was collected by the owner and brought in for necropsy. Gill and skin biopsies were negative. A bacterial culture taken from the posterior kidney showed no growth after 48 hours at 25°C (77°F).

Question	Answer		Article
Which heavy metal can leach from galvanized steel and cause mortality in fish?	Zinc toxicity is commonly associated with fish mortality after housing in a galvanized steel tank.		[[|Link to Article]]
How would you confirm your diagnosis?	When a toxin is suspected, efforts should be made to confirm the presence of the suspect contaminant in the environment and in tissue of affected fish. State veterinary diagnostic laboratories are usually able to perform these assays at a reasonable cost. In the situation described, a water sample from the tank should be frozen in an inert plastic bottle. A few freshly dead or moribund fish should be frozen in a plastic bag. These samples should then be submitted to the appropriate laboratory for analysis.		[[|Link to Article]]
How would water quality parameters affect the situation?	Toxicity of zinc to fish varies dramatically between different species of fish and water quality parameters. A number of studies have reported 96-h LC50 data in the range of 0.87–40.90 p.p.m. Zn2+ in water. In general, zinc toxicity increases as water temperature and pH increase, and total hardness decreases.		[[|Link to Article]]