Mercury concentrations in fish tissue are known to be
affected by age, length, and weight (WHO, 1990).
Freshwater biota accumulate Hg from both natural and
anthropogenic sources. Most fish naturally have background
Hg levels of 0.05–0.3ppm Hg, though small,
short-lived herbivorous species are thought to have
levels of just 0.01ppm Hg