The information on a fish mercury level chart includes the type of fish; if it is canned, fresh or frozen; the number of samples tested; and the source of the data. The chart also tells the reader when the data was collected.
The chart also shows the mean, medium, standard deviation, minimum and maximum mercury levels observed in a species of fish. Footnotes also tell which species were taken out of the table. In the case of charts that show mercury levels from 1990 to 2010, freshwater bass and pickerel are absent because they lack commercial status. Footnotes also let the reader know if any changes were made to the data.
Mercury levels are measured in parts per million. Monkfish, for example, have a mean mercury concentration of 0.181 ppm, a median mercury concentration of 0.139 ppm, a standard deviation of 0.075 ppm, a minimum mercury concentration of 0.106 ppm and a maximum mercury concentration of 0.289 ppm taken from 9 samples. The information was collected by the Food and Drug Administration between 2006 and 2008.
In other fish, such as the butterfish, the Pacific mackerel chub, the skate, the Spanish mackerel and tilefish from the Gulf of Mexico, the source of the information is the National Marine Fisheries Service.