Jonathan R. Deeds1*, Daniel E. Terlizzi1,2, and Allen R. Place1, 1University of Maryland Biotechnology Institute, Center of Marine Biotechnology, 701 East Pratt St., Suite 236, Baltimore, MD 21202, USA; 2University of Maryland Sea Grant Program and College of Agriculture and Natural Resources, College Park, MD 20742, USA
Abstract
Since 1996, three fish kill events associated with blooms of Gyrodinium galatheanum have occurred at HyRock Fish Farm, an etusarine pond production facility raising hybrid striped bass on the Chesapeake Bay, MD, USA. It has been observed at HyRock that blooms of G. galatheanum treated with copper resulted in greater mortality than blooms treated with potassium permanganate.
Gyrodinium galatheanum is a small (10-15 µm), non-thecate dinoflagellate that is found at a wide range of salinities and temperatures in the Chesapeake Bay (3-29 psu; 7-28°C) (Li et al., 2000, J. Plankton Res., 22(11), 2105-2124). G. galatheanum from Norwegian waters has previously been shown to be ichthyotoxic (Nielsen, 1993, Mar. Ecol. Prog. Ser. 95, 273-277), but no specific toxins had been identified.
We have discovered at least one substance from G. galatheanum cultures that is ichthyotoxic, cytotoxic, and hemolytic. This substance appears to be released in small amounts in healthy cultures, but is released in greater amounts upon cell damage or lysis.
We have shown both copper sulfate (CuSO4 - 2 mg/L) and potassium permanganate (KMnO4 - 4 mg/L) cause significant lysis (>70%) of this organism within 24 hrs. Further, we have shown that toxic substance(s) are released upon copper sulfate treatments > 0.5 mg/L (80% ichthyotoxicity to sheepshead minnow, Cyprinodon variegatus, larvae), but not upon potassium permanganate treatment (4 mg/L), suggesting oxidation of released cellular materials. Based on these results, it is recommended that copper sulfate not be used for treatment of blooms of this organism. Alternative oxidizing agents such as ozone are currently being evaluated.