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Abstract(s)
Metals are contaminants of great concern due to their persistence and potential toxic
effects. Some heavy metals like lead have no function in biological systems, while others
such as copper and zinc are essential for metabolism of living organisms, including fish.
Nevertheless they may exert harmful effects, depending upon concentration. Fish can be
exposed to trace metals via two main exposure routes, waterborne and dietary and their
accumulation can reach high concentrations, with time of exposure, even when the
environmental contamination levels are low. Toxicity of trace metals to fish is strongly
dependent upon abiotic and biotic factors that influence metal uptake and
bioaccumulation.
Some fish species have demonstrated the ability to inhabit polluted water bodies,
probably adjusting metabolic mechanisms to cope with exposure to contaminants. Mullet
is one of these species resistant to adverse environments that can be used as model to
investigate fish metabolic changes of adaptation. The habitat under research is a small
polluted coastal lagoon (Northwest coast, Portugal), where leaping grey mullet, Liza
saliens, were exposed to heavy metals in water and sediments and accumulated high
concentrations of Cu and Zn in their tissues. The unique characteristics of this small lagoon, such as its narrow communication with the sea, allowed the fingerlings to enter
the lagoon but not the adults to escape, resulting in fish permanency in the lagoon for
their life spans and consequently a long time exposure to contaminants. A sample of adult
mullet was monitored using different biomarkers levels to assess chronic toxicity effects.
Morphological indices of fish condition and gill osmoregulatory responses were
evaluated, as well as metal accumulation in two main organs, gill and liver. At the
biochemical level the antioxidant responses in tissues were measured to evaluate free
radical oxidants generation and plasma enzyme activities were also measured. To
complement the evaluation of metal effects on fish histological alterations were also
assessed, as they provide a definite biological end-point of historical exposure were also
assessed to complement the impact evaluation.
The results showed a different pattern of responses in each organ and a different
strategy to adjust to Cu and Zn chronic exposure.
The use of biomarkers has been useful to monitor the health of fish inhabiting
polluted ecosystems, and it could additionally reveal important adaptations to pollutantinduced
stress. This case study allowed a long-term and more realistic evaluation of the
fish stress responses to pollution, since fish lived in this habitat for 6 to 12 years.
Understanding the potential effects of trace metals and the physiological mechanisms of
adaptation, to face chronic exposure, seems crucial for population conservation purposes.
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Citation
Fernandes, Conceição; Salgado, M.A.; Fontainhas-Fernandes, A. (2008). Metabolic mechanisms of adaptation to chronic metal exposure: a case study. In Brown, Samuel E.; Welton, William C. (Eds.) Heavy Metal Pollution. Nova Science Publishers. ISBN: 978-1-61668-049-2