Copper sulfate is the most effective and commonly used protozoacide for treating captive marine fishes. Copper sulfate is most often used to treat "white spot disease" (Cryptocaryon irritans) and "velvet disease" (Amyloodinium ocellatus) of marine fishes.2 While safe and effective for most teleosts when used at prescribed doses with accurate monitoring, it is widely assumed that copper is fatally toxic to aquatic invertebrates. Many private and public aquarium habitats keep mixed populations of teleosts and invertebrates. This often presents a challenge to the clinician during the above mentioned disease outbreaks for several reasons: 1) catching and relocating certain species of fish is stressful and potentially debilitating, especially with a serious parasitic infection; 2) multiple aquaria or holding tanks will be required to house the separated animals; and 3) infectious life stages of the pathogens may remain viable in the untreated aquarium containing the invertebrates.
It has been shown that not all marine invertebrates will die when exposed to copper.1 The authors hypothesized the purple sea urchin, Arbacia punctulata, would be a good animal to test echinoderm sensitivity to copper sulfate. The therapeutic level of copper sulfate is 0.15-0.20 mg/L; and this level must be maintained for a minimum of 14 days in order to effectively treat disease.
Four 20-gallon tanks with nine urchins per tank were assembled containing only a sponge filter and sea-water made with Instant Ocean®. The urchins were acclimated for two months prior to the study. The diet consisted of kelp and shrimp, and the urchins were healthy when the study began. Each tank contained different levels of copper (tank one--control at 0.00 mg/L, tank two--0.10 mg/L, tank three--0.15 mg/L, tank four--0.20 mg/L). Copper levels and water quality parameters were tested with a Hach® 2010 spectrophotometer, except where indicated. Water quality parameters monitored included: salinity (hydrometer), temperature (floating thermometer), ammonia, nitrite, nitrate, and pH (Hach® colorimetric tests). A solution of 1 mg/ml copper sulfate (CuSO4-5H20) was prepared and used throughout the study. On day one, copper levels were tested in each tank and confirmed that all were at 0.00 mg/L. Copper levels were raised 0.05 mg/L each day until respective levels were achieved. The first mortality occurred in tank four, five days after the first addition. Tanks two and three had the first mortalities six days after the first addition. All urchins in tank four were dead within 10 days and all urchins in tank three were dead within 15 days. There was only one mortality from tank two during the copper testing, but all urchins in tank two died within 70 days following the study. There were no mortalities from tank one, the control aquarium.
The results show that copper sulfate will cause mortality in the purple sea urchin, A. punctulata, at less than therapeutic levels.
We thank Allen LaPointe and Shane Boylan for their assistance and expertise.
1. Lundebye AK, MH Depledge. 1998. Automated interpulse duration assessment (AIDA) in the shore crab Caranus maenus in response to copper exposure. Marine Biology 130: 613-620.
2. Noga EJ. 1996. Fish Disease: diagnosis and treatment. Mosby-Year Book, Inc., St. Louis.