Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
LIVINGSTON STONE NFH: Replacing Rid-ich with Formalin in Delta Smelt Egg Treatments
California-Nevada Offices , May 1, 2011
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Delta Smelt eggs treated with Rid-ich
Delta Smelt eggs treated with Rid-ich - Photo Credit: n/a
Delta Smelt eggs treated with Formalin
Delta Smelt eggs treated with Formalin - Photo Credit: n/a

The UC Davis Fish Conservation and Culture Laboratory just outside Byron, California, which raises endangered Delta Smelt (Hypomesus transpacificus), is phasing out its use of the chemical malachite green (known cancer causing agent) in an attempt to become more ecologically responsible and compliant. Malachite green is very commonly used as a commercial dye, and was formerly widely used in aquaculture to treat fish fungal infections and parasites such as ich, also known as “white spot disease.”

This common disease caused by the protozoan Ichtyopthirius is quite common to freshwater fish, and controlling it can become difficult if not caught early. A variety of chemical treatments are found to be effective in controlling the parasite, including formalin, potassium permanganate, malachite green, copper sulfate, and others. Tests were undertaken at the FCCL in an effort to replace the use of any product containing malachite green with other less ecologically harmful chemical treatments.

Through a series of experiments over the latter half of 2010, proper dosage amounts and treatment timetables have been established to treat raised Delta Smelt for ich without the use of malachite green containing products.

In January 2011, experiments were successfully performed by Jeremy Shannon of the Livingston Stone NFH and Luke Ellison of the UC Davis FCCL to find a preventative treatment for incubating Delta Smelt eggs to ward off fungal infection without the use of malachite green, formalin (37% formaldehyde) provide to be an excellent substitute .

The use of less harmful chemicals to treat these various infections is just another step in the process of understanding Delta Smelt.

Contact Info: John Rueth, 530-275-0549, john_rueth@fws.gov
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