Impacto da exposição crônica ao fenol no metabolismo, fisiologia e resposta ao estresse de juvenis de Matrinxã (Brycon cephalus: Teleostei; Characidae).
Abstract
The contamination of the aquatic environment has been responsible for
considerable losses on natural stocks of several marine and freshwater fish. Among the
many classes of chemicals dumped in aquatic system, the phenols present a great
harmful potential due to its many modes of action. These include: genotoxicity,
haematotoxicity, immunotoxicity, citotoxicity, oxidative stress and action as endocrine
disruptors. Several authors have also demonstrated phenols capability of altering fish
metabolism. Moreover because of its lipophilicity, phenol has a high bioaccumulation
potential and can, therefore, present a high risk to fish consumers. Matrinxa (Brycon
cephalus) presents a great aquaculture potential because of it growth rate (1 kg/year) and
its good acceptance for commercial feed. This fish also represents 7% of the total of
fish consumed in the Amazonas state.
The main objective of this work was to identify the metabolic, endocrine e
cellular responses of Matrinxa (Brycon cephalus) exposed to sub lethal concentrations of
phenol. In order to accomplish this, three experiments were conducted. The first one
consisted in a toxicity test designed to establish de LC-50/96h of phenol to Matrinxa.
After that the fish were exposed for 96 hours to 10% of Matrinxas LC-50. The
objective of this experiment was to look into the metabolic alterations induced by
phenol. Finally, we exposed Matrinxa for 96 hours to 1% and 10% of the LC-50 and at
the end of the exposure submitted the fish to a handling stress. The second exposure
experiment was designed to verify the responses of stress indicators (cortisol, glucose
and HSP70) to phenol intoxication and also the possible effects of exposure in the
ability of fish to respond to a second stressor.
Phenol induced many alterations on Matrinxas metabolism. We could observe
a general reduction of carbohydrate metabolism flowed by an increase in proteolysis.
Both of these effects are likely to be a response to a higher metabolic demand, which
was confirmed by an increase in oxidative metabolism. This data is contrary to the one
found in case of pesticide intoxication, indicating there was no cellular anoxia.
When considering cortisol and glucose phenol exposure did not elicit the
classical stress response observed for other stressors. These results suggest that cortisol
and glucose might not be the best indicators for chemical stress. A lower dose (0,2
ppm) clearly affected the fish ability to respond to a second stressor. The constitutive
levels of HSP70 were reduced in gills and liver. In the gills a more lasting effect was
observed. The handling stress did not affected HSP70 expression while starvation
seemed to induce a generalized reduction on the levels this particular protein. When
looking into the cellular stress response the higher dose (2,0 ppm) appears to be more
toxic. The exposition to phenol also inhibited the characteristic ionic changes in
response to stress.
Phenol intoxication affects animal metabolism and this is likely to have effects
on growth and survival. Moreover, the ability of these fish to respond to a second
stressor is reduced in both organismal and cellular levels.