Toxicity of crude oil and chemical agents used in clean-up and remediation is generally gauged by calculation of the LC50 (concentration required to kill 50% of exposed indicator species in a specified time period); nevertheless, even low non-lethal levels of chemical by-products can negatively impact animal health and well-being. The sub-lethal effects of these chemicals on growth, development, and reproduction are important to consider when assessing the full environmental impact of pollutants at the organismal level. Indeed, the sub-lethal impacts of environmental pollutants may persist for generations, long after the actual lethal impact has occurred. It is therefore preferable to have in place a rapid-response system that warns of silent (i.e., sub-lethal) and/or persistent exposure. We posit that the acute phase response of indigenous fish species can serve this purpose.
All animals respond to environmental stressors by changes in gene expression. In particular, genes encoding different stress response proteins (proteins that protect against the stressor), which are essential for the survival of a cell confronted with environmental insult, are rapidly up-regulated. Rapid, precise, and accurate measurement of key stress-induced proteins, particularly those involved in the acute-phase response, should allow indigenous (or introduced non-indigenous) animal populations to be used to evaluate the biological impact of environmental contaminants. For example, detection of the elevation of acute phase biomarkers (mRNA or protein levels) would provide an early warning that contaminants are present in the environment. Further, the magnitude of change in these biomarkers might indicate the level of impact of the inciting toxicant, and allow prediction of future consequences to organisms in that environment. Acute phase biomarkers represent the absolute first stage response of any organism to an environmental stressor and are a definitive marker of inflammatory stress. These biomarkers have only recently been evaluated in any fish species.
We recently demonstrated the up-regulation of the acute phase response in the cyprinid Danio rerio (zebrafish), wherein we can detect an increase in mRNA for C-reactive protein (CRP), serum amyloid A (SAA), and vitellogenin. All three genes were up-regulated within 2 hours of exposure to bacterial endotoxin (injected intra-peritoneal.). Sequence homology of these proteins among vertebrates suggests that we will be able to identify these genes in many other fish species, particularly those of commercial and/or ecological importance along the Alabama coast.