Fig. 1

Boxplots highlighting the systematic difference in the Ct-values for the market-sampled vs. field-sampled fish. The bold, middle line represents the median for each group; the box covers the range between the lower and upper quartiles; the whiskers extend to the last value still within 1.5 times the interquartile arrange of the relevant quartile; individual points beyond these are plotted individually as potential outliers.