Metabolomics of aquatic organisms: the new 'omics' on the block

Environmental metabolomics can be defined as the application of metabolomics to characterise the metabolism of free-living organisms obtained from the natural environment and of organisms reared under laboratory conditions, where those conditions serve to mimic scenarios encountered in the natural environment. This approach has considerable potential for characterising the responses of organisms to natural and anthropogenic stressors. The current essay introduces environmental metabolomics, discusses the challenges of measuring metabolites, and then highlights the dynamic nature of the metabolome that can be exploited to provide a holistic view of an organism's health. Dealing with metabolic variability is a considerable challenge in environmental metabolomics. Here, I propose the concept of a normal metabolic operating range (NMOR), defined as the region in metabolic space in which 95% of individuals from a population reside, with stress identified as a deviation from the NMOR. Furthermore, I emphasise the importance of genotypic and phenotypic anchoring (e.g. knowing species, gender, age) to facilitate interpretation of multivariate metabolomics data.