In a living ecosystem, organisms vary in their level of metal
accumulation depending upon their diet, trophic level, age, size,
gender and various other internal or external parameters. Assessing
the condition of an ecosystem by measuring the concentrations
of contaminants in all compartments of the ecosystem is difficult,
time consuming and labor intensive. So, for the sake of convenience
various indicator (sentinel) species are commonly used
which are exposed to the environment and could best reflect the
state of that ecosystem in a wider range (Burger and Gochfeld,
2000; Scheifler et al., 2006; Brait and Antoniosi-Filho, 2011; Falq
et al., 2011).