Modest levels of nitrate nitrogen – in the 75 to 100 mg/L range – may be more harmful to aquaculture-raised rainbow trout than producers realize. A team of scientists at the Conservation Fund's Freshwater Institute led by John Davidson documented deformities and significant behavioral changes in rainbow trout (Oncorhynchus mykiss) raised in recirculating aquaculture systems (RAS) with nitrate nitrogen concentrations at levels less than one-tenth the recommended maximum nitrate nitrogen level of 1,000 mg/L. They believe the changes were spurred by chronic exposure to nitrate nitrogen.

"The biggest surprise to us as we were trying to determine why the fish were behaving the way they were was the possibility of a connection to nitrate nitrogen," says John Davidson of the Convervation Fund's Freshwater Institute. "Because of the literature we had been used to reading, we didn't even consider nitrate nitrogen as a parameter of concern until I plotted it out and saw a very close correlation."

The research can be seen in the most recent application story: Is Chronic Exposure to Nitrate Nitrogen a Hidden Danger to Trout in Recirculating Aquaculture Systems?

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